path: root/driverlib/can.c

//*****************************************************************************
//
// can.c - Driver for the CAN module.
//
// Copyright (c) 2006-2012 Texas Instruments Incorporated.  All rights reserved.
// Software License Agreement
// 
//   Redistribution and use in source and binary forms, with or without
//   modification, are permitted provided that the following conditions
//   are met:
// 
//   Redistributions of source code must retain the above copyright
//   notice, this list of conditions and the following disclaimer.
// 
//   Redistributions in binary form must reproduce the above copyright
//   notice, this list of conditions and the following disclaimer in the
//   documentation and/or other materials provided with the  
//   distribution.
// 
//   Neither the name of Texas Instruments Incorporated nor the names of
//   its contributors may be used to endorse or promote products derived
//   from this software without specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// 
// This is part of revision 9453 of the Stellaris Peripheral Driver Library.
//
//*****************************************************************************

//*****************************************************************************
//
//! \addtogroup can_api
//! @{
//
//*****************************************************************************

#include "inc/hw_can.h"
#include "inc/hw_ints.h"
#include "inc/hw_nvic.h"
#include "inc/hw_memmap.h"
#include "inc/hw_types.h"
#include "driverlib/can.h"
#include "driverlib/debug.h"
#include "driverlib/interrupt.h"

//*****************************************************************************
//
// This is the maximum number that can be stored as an 11bit Message
// identifier.
//
//*****************************************************************************
#define CAN_MAX_11BIT_MSG_ID    0x7ff

//*****************************************************************************
//
// This is used as the loop delay for accessing the CAN controller registers.
//
//*****************************************************************************
#define CAN_RW_DELAY            5

//*****************************************************************************
//
// The maximum CAN bit timing divisor is 19.
//
//*****************************************************************************
#define CAN_MAX_BIT_DIVISOR     19

//*****************************************************************************
//
// The minimum CAN bit timing divisor is 4.
//
//*****************************************************************************
#define CAN_MIN_BIT_DIVISOR     4

//*****************************************************************************
//
// The maximum CAN pre-divisor is 1024.
//
//*****************************************************************************
#define CAN_MAX_PRE_DIVISOR     1024

//*****************************************************************************
//
// The minimum CAN pre-divisor is 1.
//
//*****************************************************************************
#define CAN_MIN_PRE_DIVISOR     1

//*****************************************************************************
//
// Converts a set of CAN bit timing values into the value that needs to be
// programmed into the CAN_BIT register to achieve those timings.
//
//*****************************************************************************
#define CAN_BIT_VALUE(seg1, seg2, sjw)                                        \
                                ((((seg1 - 1) << CAN_BIT_TSEG1_S) &           \
                                  CAN_BIT_TSEG1_M) |                          \
                                 (((seg2 - 1) << CAN_BIT_TSEG2_S) &           \
                                  CAN_BIT_TSEG2_M) |                          \
                                 (((sjw - 1) << CAN_BIT_SJW_S) &              \
                                  CAN_BIT_SJW_M))

//*****************************************************************************
//
// This table is used by the CANBitRateSet() API as the register defaults for
// the bit timing values.
//
//*****************************************************************************
static const unsigned short g_usCANBitValues[] =
{
    CAN_BIT_VALUE(2, 1, 1),     // 4 clocks/bit
    CAN_BIT_VALUE(3, 1, 1),     // 5 clocks/bit
    CAN_BIT_VALUE(3, 2, 2),     // 6 clocks/bit
    CAN_BIT_VALUE(4, 2, 2),     // 7 clocks/bit
    CAN_BIT_VALUE(4, 3, 3),     // 8 clocks/bit
    CAN_BIT_VALUE(5, 3, 3),     // 9 clocks/bit
    CAN_BIT_VALUE(5, 4, 4),     // 10 clocks/bit
    CAN_BIT_VALUE(6, 4, 4),     // 11 clocks/bit
    CAN_BIT_VALUE(6, 5, 4),     // 12 clocks/bit
    CAN_BIT_VALUE(7, 5, 4),     // 13 clocks/bit
    CAN_BIT_VALUE(7, 6, 4),     // 14 clocks/bit
    CAN_BIT_VALUE(8, 6, 4),     // 15 clocks/bit
    CAN_BIT_VALUE(8, 7, 4),     // 16 clocks/bit
    CAN_BIT_VALUE(9, 7, 4),     // 17 clocks/bit
    CAN_BIT_VALUE(9, 8, 4),     // 18 clocks/bit
    CAN_BIT_VALUE(10, 8, 4)     // 19 clocks/bit
};

//*****************************************************************************
//
//! \internal
//! Checks a CAN base address.
//!
//! \param ulBase is the base address of the CAN controller.
//!
//! This function determines if a CAN controller base address is valid.
//!
//! \return Returns \b true if the base address is valid and \b false
//! otherwise.
//
//*****************************************************************************
#ifdef DEBUG
static tBoolean
CANBaseValid(unsigned long ulBase)
{
    return((ulBase == CAN0_BASE) || (ulBase == CAN1_BASE) ||
           (ulBase == CAN2_BASE));
}
#endif

//*****************************************************************************
//
//! \internal
//!
//! Returns the CAN controller interrupt number.
//!
//! \param ulBase is the base address of the selected CAN controller
//!
//! Given a CAN controller base address, this function returns the
//! corresponding interrupt number.
//!
//! This function replaces the original CANGetIntNumber() API and performs the
//! same actions.  A macro is provided in <tt>can.h</tt> to map the original
//! API to this API.
//!
//! \return Returns a CAN interrupt number, or -1 if \e ulPort is invalid.
//
//*****************************************************************************
static long
CANIntNumberGet(unsigned long ulBase)
{
    long lIntNumber;

    //
    // Return the interrupt number for the given CAN controller.
    //
    switch(ulBase)
    {
        //
        // Return the interrupt number for CAN 0
        //
        case CAN0_BASE:
        {
            lIntNumber = INT_CAN0;
            break;
        }

        //
        // Return the interrupt number for CAN 1
        //
        case CAN1_BASE:
        {
            lIntNumber = INT_CAN1;
            break;
        }

        //
        // Return the interrupt number for CAN 2
        //
        case CAN2_BASE:
        {
            lIntNumber = INT_CAN2;
            break;
        }

        //
        // Return -1 to indicate a bad address was passed in.
        //
        default:
        {
            lIntNumber = -1;
        }
    }
    return(lIntNumber);
}

//*****************************************************************************
//
//! \internal
//!
//! Reads a CAN controller register.
//!
//! \param ulRegAddress is the full address of the CAN register to be read.
//!
//! This function performs the necessary synchronization to read from a CAN
//! controller register.
//!
//! This function replaces the original CANReadReg() API and performs the same
//! actions.  A macro is provided in <tt>can.h</tt> to map the original API to
//! this API.
//!
//! \note This function provides the delay required to access CAN registers.
//! This delay is required when accessing CAN registers directly.
//!
//! \return Returns the value read from the register.
//
//*****************************************************************************
static unsigned long
CANRegRead(unsigned long ulRegAddress)
{
    volatile unsigned long ulDelay;
    unsigned long ulRetVal;
    unsigned long ulIntNumber;
    unsigned long ulReenableInts;

    //
    // Get the CAN interrupt number from the register base address.
    //
    ulIntNumber = CANIntNumberGet(ulRegAddress & 0xfffff000);

    //
    // Make sure that the CAN base address was valid.
    //
    ASSERT(ulIntNumber != (unsigned long)-1);

    //
    // Remember current state so that CAN interrupts are only re-enabled if
    // they were already enabled.
    //
    ulReenableInts = HWREG(NVIC_EN1) & (1 << (ulIntNumber - 48));

    //
    // If the CAN interrupt was enabled then disable it.
    //
    if(ulReenableInts)
    {
        IntDisable(ulIntNumber);
    }

    //
    // Trigger the initial read to the CAN controller.  The value returned at
    // this point is not valid.
    //
    HWREG(ulRegAddress);

    //
    // This delay is necessary for the CAN have the correct data on the bus.
    //
    for(ulDelay = 0; ulDelay < CAN_RW_DELAY; ulDelay++)
    {
    }

    //
    // Do the final read that has the valid value of the register.
    //
    ulRetVal = HWREG(ulRegAddress);

    //
    // Enable CAN interrupts if they were enabled before this call.
    //
    if(ulReenableInts)
    {
        IntEnable(ulIntNumber);
    }

    return(ulRetVal);
}

//*****************************************************************************
//
//! \internal
//!
//! Writes a CAN controller register.
//!
//! \param ulRegAddress is the full address of the CAN register to be written.
//! \param ulRegValue is the value to write into the register specified by
//! \e ulRegAddress.
//!
//! This function takes care of the synchronization necessary to write to a
//! CAN controller register.
//!
//! This function replaces the original CANWriteReg() API and performs the same
//! actions.  A macro is provided in <tt>can.h</tt> to map the original API to
//! this API.
//!
//! \note The delays in this function are required when accessing CAN registers
//! directly.
//!
//! \return None.
//
//*****************************************************************************
static void
CANRegWrite(unsigned long ulRegAddress, unsigned long ulRegValue)
{
    volatile unsigned long ulDelay;

    //
    // Trigger the initial write to the CAN controller.  The value will not make
    // it out to the CAN controller for CAN_RW_DELAY cycles.
    //
    HWREG(ulRegAddress) = ulRegValue;

    //
    // Delay to allow the CAN controller to receive the new data.
    //
    for(ulDelay = 0; ulDelay < CAN_RW_DELAY; ulDelay++)
    {
    }
}

//*****************************************************************************
//
//! \internal
//!
//! Copies data from a buffer to the CAN Data registers.
//!
//! \param pucData is a pointer to the data to be written out to the CAN
//! controller's data registers.
//! \param pulRegister is an unsigned long pointer to the first register of the
//! CAN controller's data registers.  For example, in order to use the IF1
//! register set on CAN controller 0, the value would be: \b CAN0_BASE \b +
//! \b CAN_O_IF1DA1.
//! \param iSize is the number of bytes to copy into the CAN controller.
//!
//! This function takes the steps necessary to copy data from a contiguous
//! buffer in memory into the non-contiguous data registers used by the CAN
//! controller.  This function is rarely used outside of the CANMessageSet()
//! function.
//!
//! This function replaces the original CANWriteDataReg() API and performs the
//! same actions.  A macro is provided in <tt>can.h</tt> to map the original
//! API to this API.
//!
//! \return None.
//
//*****************************************************************************
static void
CANDataRegWrite(unsigned char *pucData, unsigned long *pulRegister,
                unsigned long ulSize)
{
    unsigned long ulIdx, ulValue;

    //
    // Loop always copies 1 or 2 bytes per iteration.
    //
    for(ulIdx = 0; ulIdx < ulSize; )
    {

        //
        // Write out the data 16 bits at a time since this is how the registers
        // are aligned in memory.
        //
        ulValue = pucData[ulIdx++];

        //
        // Only write the second byte if needed otherwise it will be zero.
        //
        if(ulIdx < ulSize)
        {
            ulValue |= (pucData[ulIdx++] << 8);
        }
        CANRegWrite((unsigned long)(pulRegister++), ulValue);
    }
}

//*****************************************************************************
//
//! \internal
//!
//! Copies data from a buffer to the CAN Data registers.
//!
//! \param pucData is a pointer to the location to store the data read from the
//! CAN controller's data registers.
//! \param pulRegister is an unsigned long pointer to the first register of the
//! CAN controller's data registers.  For example, in order to use the IF1
//! register set on CAN controller 1, the value would be: \b CAN0_BASE \b +
//! \b CAN_O_IF1DA1.
//! \param iSize is the number of bytes to copy from the CAN controller.
//!
//! This function takes the steps necessary to copy data to a contiguous buffer
//! in memory from the non-contiguous data registers used by the CAN
//! controller.  This function is rarely used outside of the CANMessageGet()
//! function.
//!
//! This function replaces the original CANReadDataReg() API and performs the
//! same actions.  A macro is provided in <tt>can.h</tt> to map the original
//! API to this API.
//!
//! \return None.
//
//*****************************************************************************
static void
CANDataRegRead(unsigned char *pucData, unsigned long *pulRegister,
               unsigned long ulSize)
{
    unsigned long ulIdx, ulValue;

    //
    // Loop always copies 1 or 2 bytes per iteration.
    //
    for(ulIdx = 0; ulIdx < ulSize; )
    {
        //
        // Read out the data 16 bits at a time since this is how the registers
        // are aligned in memory.
        //
        ulValue = CANRegRead((unsigned long)(pulRegister++));

        //
        // Store the first byte.
        //
        pucData[ulIdx++] = (unsigned char)ulValue;

        //
        // Only read the second byte if needed.
        //
        if(ulIdx < ulSize)
        {
            pucData[ulIdx++] = (unsigned char)(ulValue >> 8);
        }
    }
}

//*****************************************************************************
//
//! Initializes the CAN controller after reset.
//!
//! \param ulBase is the base address of the CAN controller.
//!
//! After reset, the CAN controller is left in the disabled state.  However,
//! the memory used for message objects contains undefined values and must be
//! cleared prior to enabling the CAN controller the first time.  This prevents
//! unwanted transmission or reception of data before the message objects are
//! configured.  This function must be called before enabling the controller
//! the first time.
//!
//! \return None.
//
//*****************************************************************************
void
CANInit(unsigned long ulBase)
{
    unsigned long ulMsg;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Place CAN controller in init state, regardless of previous state.  This
    // will put controller in idle, and allow the message object RAM to be
    // programmed.
    //
    CANRegWrite(ulBase + CAN_O_CTL, CAN_CTL_INIT);

    //
    // Wait for busy bit to clear
    //
    while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
    {
    }

    //
    // Clear the message value bit in the arbitration register.  This indicates
    // the message is not valid and is a "safe" condition to leave the message
    // object.  The same arb reg is used to program all the message objects.
    //
    CANRegWrite(ulBase + CAN_O_IF1CMSK, CAN_IF1CMSK_WRNRD | CAN_IF1CMSK_ARB |
                CAN_IF1CMSK_CONTROL);
    CANRegWrite(ulBase + CAN_O_IF1ARB2, 0);
    CANRegWrite(ulBase + CAN_O_IF1MCTL, 0);

    //
    // Loop through to program all 32 message objects
    //
    for(ulMsg = 1; ulMsg <= 32; ulMsg++)
    {
        //
        // Wait for busy bit to clear
        //
        while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
        {
        }

        //
        // Initiate programming the message object
        //
        CANRegWrite(ulBase + CAN_O_IF1CRQ, ulMsg);
    }

    //
    // Make sure that the interrupt and new data flags are updated for the
    // message objects.
    //
    CANRegWrite(ulBase + CAN_O_IF1CMSK, CAN_IF1CMSK_NEWDAT |
                CAN_IF1CMSK_CLRINTPND);

    //
    // Loop through to program all 32 message objects
    //
    for(ulMsg = 1; ulMsg <= 32; ulMsg++)
    {
        //
        // Wait for busy bit to clear.
        //
        while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
        {
        }

        //
        // Initiate programming the message object
        //
        CANRegWrite(ulBase + CAN_O_IF1CRQ, ulMsg);
    }

    //
    // Acknowledge any pending status interrupts.
    //
    CANRegRead(ulBase + CAN_O_STS);
}

//*****************************************************************************
//
//! Enables the CAN controller.
//!
//! \param ulBase is the base address of the CAN controller to enable.
//!
//! Enables the CAN controller for message processing.  Once enabled, the
//! controller automatically transmits any pending frames, and processes any
//! received frames.  The controller can be stopped by calling CANDisable().
//! Prior to calling CANEnable(), CANInit() should have been called to
//! initialize the controller and the CAN bus clock should be configured by
//! calling CANBitTimingSet().
//!
//! \return None.
//
//*****************************************************************************
void
CANEnable(unsigned long ulBase)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Clear the init bit in the control register.
    //
    CANRegWrite(ulBase + CAN_O_CTL,
                CANRegRead(ulBase + CAN_O_CTL) & ~CAN_CTL_INIT);
}

//*****************************************************************************
//
//! Disables the CAN controller.
//!
//! \param ulBase is the base address of the CAN controller to disable.
//!
//! Disables the CAN controller for message processing.  When disabled, the
//! controller no longer automatically processes data on the CAN bus.  The
//! controller can be restarted by calling CANEnable().  The state of the CAN
//! controller and the message objects in the controller are left as they were
//! before this call was made.
//!
//! \return None.
//
//*****************************************************************************
void
CANDisable(unsigned long ulBase)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Set the init bit in the control register.
    //
    CANRegWrite(ulBase + CAN_O_CTL,
                CANRegRead(ulBase + CAN_O_CTL) | CAN_CTL_INIT);
}

//*****************************************************************************
//
//! Reads the current settings for the CAN controller bit timing.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param pClkParms is a pointer to a structure to hold the timing parameters.
//!
//! This function reads the current configuration of the CAN controller bit
//! clock timing and stores the resulting information in the structure
//! supplied by the caller.  Refer to CANBitTimingSet() for the meaning of the
//! values that are returned in the structure pointed to by \e pClkParms.
//!
//! This function replaces the original CANGetBitTiming() API and performs the
//! same actions.  A macro is provided in <tt>can.h</tt> to map the original
//! API to this API.
//!
//! \return None.
//
//*****************************************************************************
void
CANBitTimingGet(unsigned long ulBase, tCANBitClkParms *pClkParms)
{
    unsigned long ulBitReg;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT(pClkParms != 0);

    //
    // Read out all the bit timing values from the CAN controller registers.
    //
    ulBitReg = CANRegRead(ulBase + CAN_O_BIT);

    //
    // Set the phase 2 segment.
    //
    pClkParms->ulPhase2Seg =
        ((ulBitReg & CAN_BIT_TSEG2_M) >> CAN_BIT_TSEG2_S) + 1;

    //
    // Set the phase 1 segment.
    //
    pClkParms->ulSyncPropPhase1Seg =
        ((ulBitReg & CAN_BIT_TSEG1_M) >> CAN_BIT_TSEG1_S) + 1;

    //
    // Set the synchronous jump width.
    //
    pClkParms->ulSJW = ((ulBitReg & CAN_BIT_SJW_M) >> CAN_BIT_SJW_S) + 1;

    //
    // Set the pre-divider for the CAN bus bit clock.
    //
    pClkParms->ulQuantumPrescaler =
        ((ulBitReg & CAN_BIT_BRP_M) |
         ((CANRegRead(ulBase + CAN_O_BRPE) & CAN_BRPE_BRPE_M) << 6)) + 1;
}

//*****************************************************************************
//
//! Sets the CAN bit timing values to a nominal setting based on a desired
//! bit rate.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulSourceClock is the system clock for the device in Hz.
//! \param ulBitRate is the desired bit rate.
//!
//! This function sets the CAN bit timing for the bit rate passed in the
//! \e ulBitRate parameter based on the \e ulSourceClock parameter.  Because the
//! CAN clock is based off of the system clock, the calling function should pass
//! in the source clock rate either by retrieving it from SysCtlClockGet() or
//! using a specific value in Hz.  The CAN bit timing is calculated assuming a
//! minimal amount of propagation delay, which works for most cases where
//! the network length is short.  If tighter timing requirements or longer
//! network lengths are needed, then the CANBitTimingSet() function is
//! available for full customization of all of the CAN bit timing values.
//! Because not all bit rates can be matched exactly, the bit rate is set to
//! the value closest to the desired bit rate without being higher than the
//! \e ulBitRate value.
//!
//! \note On some devices the source clock is fixed at 8MHz so the
//! \e ulSourceClock should be set to 8000000.
//!
//! \return This function returns the bit rate that the CAN controller was
//! configured to use or it returns 0 to indicate that the bit rate was not
//! changed because the requested bit rate was not valid.
//!
//*****************************************************************************
unsigned long
CANBitRateSet(unsigned long ulBase, unsigned long ulSourceClock,
              unsigned long ulBitRate)
{
    unsigned long ulDesiredRatio;
    unsigned long ulCANBits;
    unsigned long ulPreDivide;
    unsigned long ulRegValue;
    unsigned short usCANCTL;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT(ulSourceClock != 0);
    ASSERT(ulBitRate != 0);

    //
    // Calculate the desired clock rate.
    //
    ulDesiredRatio = ulSourceClock / ulBitRate;

    //
    // Make sure that the ratio of CAN bit rate to processor clock is not too
    // small or too large.
    //
    ASSERT(ulDesiredRatio <= (CAN_MAX_PRE_DIVISOR * CAN_MAX_BIT_DIVISOR));
    ASSERT(ulDesiredRatio >= (CAN_MIN_PRE_DIVISOR * CAN_MIN_BIT_DIVISOR));

    //
    // Make sure that the Desired Ratio is not too large.  This enforces the
    // requirement that the bit rate is larger than requested.
    //
    if((ulSourceClock / ulDesiredRatio) > ulBitRate)
    {
        ulDesiredRatio += 1;
    }

    //
    // Check all possible values to find a matching value.
    //
    while(ulDesiredRatio <= (CAN_MAX_PRE_DIVISOR * CAN_MAX_BIT_DIVISOR))
    {
        //
        // Loop through all possible CAN bit divisors.
        //
        for(ulCANBits = CAN_MAX_BIT_DIVISOR; ulCANBits >= CAN_MIN_BIT_DIVISOR;
            ulCANBits--)
        {
            //
            // For a given CAN bit divisor save the pre divisor.
            //
            ulPreDivide = ulDesiredRatio / ulCANBits;

            //
            // If the calculated divisors match the desired clock ratio then
            // return these bit rate and set the CAN bit timing.
            //
            if((ulPreDivide * ulCANBits) == ulDesiredRatio)
            {
                //
                // Start building the bit timing value by adding the bit timing
                // in time quanta.
                //
                ulRegValue = g_usCANBitValues[ulCANBits - CAN_MIN_BIT_DIVISOR];

                //
                // To set the bit timing register, the controller must be placed
                // in init mode (if not already), and also configuration change
                // bit enabled.  The state of the register should be saved
                // so it can be restored.
                //
                usCANCTL = CANRegRead(ulBase + CAN_O_CTL);
                CANRegWrite(ulBase + CAN_O_CTL,
                            usCANCTL | CAN_CTL_INIT | CAN_CTL_CCE);

                //
                // Now add in the pre-scalar on the bit rate.
                //
                ulRegValue |= ((ulPreDivide - 1) & CAN_BIT_BRP_M);

                //
                // Set the clock bits in the and the lower bits of the
                // pre-scalar.
                //
                CANRegWrite(ulBase + CAN_O_BIT, ulRegValue);

                //
                // Set the divider upper bits in the extension register.
                //
                CANRegWrite(ulBase + CAN_O_BRPE,
                            ((ulPreDivide - 1) >> 6) & CAN_BRPE_BRPE_M);

                //
                // Restore the saved CAN Control register.
                //
                CANRegWrite(ulBase + CAN_O_CTL, usCANCTL);

                //
                // Return the computed bit rate.
                //
                return(ulSourceClock / ( ulPreDivide * ulCANBits));
            }
        }

        //
        // Move the divisor up one and look again.  Only in rare cases are
        // more than 2 loops required to find the value.
        //
        ulDesiredRatio++;
    }

    //
    // A valid combination could not be found, so return 0 to indicate that the
    // bit rate was not changed.
    //
    return(0);
}

//*****************************************************************************
//
//! Configures the CAN controller bit timing.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param pClkParms points to the structure with the clock parameters.
//!
//! Configures the various timing parameters for the CAN bus bit timing:
//! Propagation segment, Phase Buffer 1 segment, Phase Buffer 2 segment, and
//! the Synchronization Jump Width.  The values for Propagation and Phase
//! Buffer 1 segments are derived from the combination
//! \e pClkParms->ulSyncPropPhase1Seg parameter.  Phase Buffer 2 is determined
//! from the \e pClkParms->ulPhase2Seg parameter.  These two parameters, along
//! with \e pClkParms->ulSJW are based in units of bit time quanta.  The actual
//! quantum time is determined by the \e pClkParms->ulQuantumPrescaler value,
//! which specifies the divisor for the CAN module clock.
//!
//! The total bit time, in quanta, is the sum of the two Seg parameters,
//! as follows:
//!
//! bit_time_q = ulSyncPropPhase1Seg + ulPhase2Seg + 1
//!
//! Note that the Sync_Seg is always one quantum in duration, and is added
//! to derive the correct duration of Prop_Seg and Phase1_Seg.
//!
//! The equation to determine the actual bit rate is as follows:
//!
//! CAN Clock /
//! ((\e ulSyncPropPhase1Seg + \e ulPhase2Seg + 1) * (\e ulQuantumPrescaler))
//!
//! Thus with \e ulSyncPropPhase1Seg = 4, \e ulPhase2Seg = 1,
//! \e ulQuantumPrescaler = 2 and an 8 MHz CAN clock, the bit rate is
//! (8 MHz) / ((5 + 2 + 1) * 2) or 500 Kbit/sec.
//!
//! This function replaces the original CANSetBitTiming() API and performs the
//! same actions.  A macro is provided in <tt>can.h</tt> to map the original
//! API to this API.
//!
//! \return None.
//
//*****************************************************************************
void
CANBitTimingSet(unsigned long ulBase, tCANBitClkParms *pClkParms)
{
    unsigned long ulBitReg, ulSavedInit;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT(pClkParms != 0);

    //
    // The phase 1 segment must be in the range from 2 to 16.
    //
    ASSERT((pClkParms->ulSyncPropPhase1Seg >= 2) &&
           (pClkParms->ulSyncPropPhase1Seg <= 16));

    //
    // The phase 2 segment must be in the range from 1 to 8.
    //
    ASSERT((pClkParms->ulPhase2Seg >= 1) && (pClkParms->ulPhase2Seg <= 8));

    //
    // The synchronous jump windows must be in the range from 1 to 4.
    //
    ASSERT((pClkParms->ulSJW >= 1) && (pClkParms->ulSJW <= 4));

    //
    // The CAN clock pre-divider must be in the range from 1 to 1024.
    //
    ASSERT((pClkParms->ulQuantumPrescaler <= 1024) &&
           (pClkParms->ulQuantumPrescaler >= 1));

    //
    // To set the bit timing register, the controller must be placed in init
    // mode (if not already), and also configuration change bit enabled.  State
    // of the init bit should be saved so it can be restored at the end.
    //
    ulSavedInit = CANRegRead(ulBase + CAN_O_CTL);
    CANRegWrite(ulBase + CAN_O_CTL, ulSavedInit | CAN_CTL_INIT | CAN_CTL_CCE);

    //
    // Set the bit fields of the bit timing register according to the parms.
    //
    ulBitReg = (((pClkParms->ulPhase2Seg - 1) << CAN_BIT_TSEG2_S) &
                CAN_BIT_TSEG2_M);
    ulBitReg |= (((pClkParms->ulSyncPropPhase1Seg - 1) << CAN_BIT_TSEG1_S) &
                 CAN_BIT_TSEG1_M);
    ulBitReg |= ((pClkParms->ulSJW - 1) << CAN_BIT_SJW_S) & CAN_BIT_SJW_M;
    ulBitReg |= (pClkParms->ulQuantumPrescaler - 1) & CAN_BIT_BRP_M;
    CANRegWrite(ulBase + CAN_O_BIT, ulBitReg);

    //
    // Set the divider upper bits in the extension register.
    //
    CANRegWrite(ulBase + CAN_O_BRPE,
                ((pClkParms->ulQuantumPrescaler - 1) >> 6) & CAN_BRPE_BRPE_M);

    //
    // Clear the config change bit, and restore the init bit.
    //
    ulSavedInit &= ~CAN_CTL_CCE;

    //
    // If Init was not set before, then clear it.
    //
    if(ulSavedInit & CAN_CTL_INIT)
    {
        ulSavedInit &= ~CAN_CTL_INIT;
    }
    CANRegWrite(ulBase + CAN_O_CTL, ulSavedInit);
}

//*****************************************************************************
//
//! Registers an interrupt handler for the CAN controller.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param pfnHandler is a pointer to the function to be called when the
//! enabled CAN interrupts occur.
//!
//! This function registers the interrupt handler in the interrupt vector
//! table, and enables CAN interrupts on the interrupt controller; specific CAN
//! interrupt sources must be enabled using CANIntEnable().  The interrupt
//! handler being registered must clear the source of the interrupt using
//! CANIntClear().
//!
//! If the application is using a static interrupt vector table stored in
//! flash, then it is not necessary to register the interrupt handler this way.
//! Instead, IntEnable() should be used to enable CAN interrupts on the
//! interrupt controller.
//!
//! \sa IntRegister() for important information about registering interrupt
//! handlers.
//!
//! \return None.
//
//*****************************************************************************
void
CANIntRegister(unsigned long ulBase, void (*pfnHandler)(void))
{
    unsigned long ulIntNumber;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Get the actual interrupt number for this CAN controller.
    //
    ulIntNumber = CANIntNumberGet(ulBase);

    //
    // Register the interrupt handler.
    //
    IntRegister(ulIntNumber, pfnHandler);

    //
    // Enable the Ethernet interrupt.
    //
    IntEnable(ulIntNumber);
}

//*****************************************************************************
//
//! Unregisters an interrupt handler for the CAN controller.
//!
//! \param ulBase is the base address of the controller.
//!
//! This function unregisters the previously registered interrupt handler and
//! disables the interrupt in the interrupt controller.
//!
//! \sa IntRegister() for important information about registering interrupt
//! handlers.
//!
//! \return None.
//
//*****************************************************************************
void
CANIntUnregister(unsigned long ulBase)
{
    unsigned long ulIntNumber;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Get the actual interrupt number for this CAN controller.
    //
    ulIntNumber = CANIntNumberGet(ulBase);

    //
    // Disable the CAN interrupt.
    //
    IntDisable(ulIntNumber);

    //
    // Register the interrupt handler.
    //
    IntUnregister(ulIntNumber);
}

//*****************************************************************************
//
//! Enables individual CAN controller interrupt sources.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulIntFlags is the bit mask of the interrupt sources to be enabled.
//!
//! This function enables specific interrupt sources of the CAN controller.
//! Only enabled sources cause a processor interrupt.
//!
//! The \e ulIntFlags parameter is the logical OR of any of the following:
//!
//! - \b CAN_INT_ERROR - a controller error condition has occurred
//! - \b CAN_INT_STATUS - a message transfer has completed, or a bus error has
//! been detected
//! - \b CAN_INT_MASTER - allow CAN controller to generate interrupts
//!
//! In order to generate any interrupts, \b CAN_INT_MASTER must be enabled.
//! Further, for any particular transaction from a message object to generate
//! an interrupt, that message object must have interrupts enabled (see
//! CANMessageSet()).  \b CAN_INT_ERROR will generate an interrupt if the
//! controller enters the ``bus off'' condition, or if the error counters reach
//! a limit.  \b CAN_INT_STATUS generates an interrupt under quite a few
//! status conditions and may provide more interrupts than the application
//! needs to handle.  When an interrupt occurs, use CANIntStatus() to determine
//! the cause.
//!
//! \return None.
//
//*****************************************************************************
void
CANIntEnable(unsigned long ulBase, unsigned long ulIntFlags)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT((ulIntFlags & ~(CAN_CTL_EIE | CAN_CTL_SIE | CAN_CTL_IE)) == 0);

    //
    // Enable the specified interrupts.
    //
    CANRegWrite(ulBase + CAN_O_CTL,
                CANRegRead(ulBase + CAN_O_CTL) | ulIntFlags);
}

//*****************************************************************************
//
//! Disables individual CAN controller interrupt sources.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulIntFlags is the bit mask of the interrupt sources to be disabled.
//!
//! Disables the specified CAN controller interrupt sources.  Only enabled
//! interrupt sources can cause a processor interrupt.
//!
//! The \e ulIntFlags parameter has the same definition as in the
//! CANIntEnable() function.
//!
//! \return None.
//
//*****************************************************************************
void
CANIntDisable(unsigned long ulBase, unsigned long ulIntFlags)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT((ulIntFlags & ~(CAN_CTL_EIE | CAN_CTL_SIE | CAN_CTL_IE)) == 0);

    //
    // Disable the specified interrupts.
    //
    CANRegWrite(ulBase + CAN_O_CTL,
                CANRegRead(ulBase + CAN_O_CTL) & ~(ulIntFlags));
}

//*****************************************************************************
//
//! Returns the current CAN controller interrupt status.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param eIntStsReg indicates which interrupt status register to read
//!
//! This function returns the value of one of two interrupt status registers.
//! The interrupt status register read is determined by the \e eIntStsReg
//! parameter, which can have one of the following values:
//!
//! - \b CAN_INT_STS_CAUSE - indicates the cause of the interrupt
//! - \b CAN_INT_STS_OBJECT - indicates pending interrupts of all message
//! objects
//!
//! \b CAN_INT_STS_CAUSE returns the value of the controller interrupt register
//! and indicates the cause of the interrupt. The value returned is
//! \b CAN_INT_INTID_STATUS if the cause is a status interrupt.  In this case,
//! the status register should be read with the CANStatusGet() function.
//! Calling this function to read the status also clears the status
//! interrupt.  If the value of the interrupt register is in the range 1-32,
//! then this indicates the number of the highest priority message object that
//! has an interrupt pending.  The message object interrupt can be cleared by
//! using the CANIntClear() function, or by reading the message using
//! CANMessageGet() in the case of a received message.  The interrupt handler
//! can read the interrupt status again to make sure all pending interrupts are
//! cleared before returning from the interrupt.
//!
//! \b CAN_INT_STS_OBJECT returns a bit mask indicating which message objects
//! have pending interrupts.  This value can be used to discover all of the
//! pending interrupts at once, as opposed to repeatedly reading the interrupt
//! register by using \b CAN_INT_STS_CAUSE.
//!
//! \return Returns the value of one of the interrupt status registers.
//
//*****************************************************************************
unsigned long
CANIntStatus(unsigned long ulBase, tCANIntStsReg eIntStsReg)
{
    unsigned long ulStatus;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // See which status the caller is looking for.
    //
    switch(eIntStsReg)
    {
        //
        // The caller wants the global interrupt status for the CAN controller
        // specified by ulBase.
        //
        case CAN_INT_STS_CAUSE:
        {
            ulStatus = CANRegRead(ulBase + CAN_O_INT);
            break;
        }

        //
        // The caller wants the current message status interrupt for all
        // messages.
        //
        case CAN_INT_STS_OBJECT:
        {
            //
            // Read and combine both 16 bit values into one 32bit status.
            //
            ulStatus = (CANRegRead(ulBase + CAN_O_MSG1INT) &
                        CAN_MSG1INT_INTPND_M);
            ulStatus |= (CANRegRead(ulBase + CAN_O_MSG2INT) << 16);
            break;
        }

        //
        // Request was for unknown status so just return 0.
        //
        default:
        {
            ulStatus = 0;
            break;
        }
    }

    //
    // Return the interrupt status value
    //
    return(ulStatus);
}

//*****************************************************************************
//
//! Clears a CAN interrupt source.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulIntClr is a value indicating which interrupt source to clear.
//!
//! This function can be used to clear a specific interrupt source.  The
//! \e ulIntClr parameter should be one of the following values:
//!
//! - \b CAN_INT_INTID_STATUS - Clears a status interrupt.
//! - 1-32 - Clears the specified message object interrupt
//!
//! It is not necessary to use this function to clear an interrupt.  This
//! function should only be used if the application wants to clear an interrupt
//! source without taking the normal interrupt action.
//!
//! Normally, the status interrupt is cleared by reading the controller status
//! using CANStatusGet().  A specific message object interrupt is normally
//! cleared by reading the message object using CANMessageGet().
//!
//! \note Because there is a write buffer in the Cortex-M processor, it may
//! take several clock cycles before the interrupt source is actually cleared.
//! Therefore, it is recommended that the interrupt source be cleared early in
//! the interrupt handler (as opposed to the very last action) to avoid
//! returning from the interrupt handler before the interrupt source is
//! actually cleared.  Failure to do so may result in the interrupt handler
//! being immediately reentered (because the interrupt controller still sees
//! the interrupt source asserted).
//!
//! \return None.
//
//*****************************************************************************
void
CANIntClear(unsigned long ulBase, unsigned long ulIntClr)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT((ulIntClr == CAN_INT_INTID_STATUS) ||
           ((ulIntClr>=1) && (ulIntClr <=32)));

    if(ulIntClr == CAN_INT_INTID_STATUS)
    {
        //
        // Simply read and discard the status to clear the interrupt.
        //
        CANRegRead(ulBase + CAN_O_STS);
    }
    else
    {
        //
        // Wait to be sure that this interface is not busy.
        //
        while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
        {
        }

        //
        // Only change the interrupt pending state by setting only the
        // CAN_IF1CMSK_CLRINTPND bit.
        //
        CANRegWrite(ulBase + CAN_O_IF1CMSK, CAN_IF1CMSK_CLRINTPND);

        //
        // Send the clear pending interrupt command to the CAN controller.
        //
        CANRegWrite(ulBase + CAN_O_IF1CRQ, ulIntClr & CAN_IF1CRQ_MNUM_M);

        //
        // Wait to be sure that this interface is not busy.
        //
        while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
        {
        }
    }
}

//*****************************************************************************
//
//! Sets the CAN controller automatic retransmission behavior.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param bAutoRetry enables automatic retransmission.
//!
//! This function enables or disables automatic retransmission of messages with
//! detected errors.  If \e bAutoRetry is \b true, then automatic
//! retransmission is enabled, otherwise it is disabled.
//!
//! \return None.
//
//*****************************************************************************
void
CANRetrySet(unsigned long ulBase, tBoolean bAutoRetry)
{
    unsigned long ulCtlReg;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    ulCtlReg = CANRegRead(ulBase + CAN_O_CTL);

    //
    // Conditionally set the DAR bit to enable/disable auto-retry.
    //
    if(bAutoRetry)
    {
        //
        // Clearing the DAR bit tells the controller to not disable the
        // auto-retry of messages which were not transmitted or received
        // correctly.
        //
        ulCtlReg &= ~CAN_CTL_DAR;
    }
    else
    {
        //
        // Setting the DAR bit tells the controller to disable the auto-retry
        // of messages which were not transmitted or received correctly.
        //
        ulCtlReg |= CAN_CTL_DAR;
    }

    CANRegWrite(ulBase + CAN_O_CTL, ulCtlReg);
}

//*****************************************************************************
//
//! Returns the current setting for automatic retransmission.
//!
//! \param ulBase is the base address of the CAN controller.
//!
//! This function reads the current setting for automatic retransmission in the CAN
//! controller and returns it to the caller.
//!
//! \return Returns \b true if automatic retransmission is enabled, \b false
//! otherwise.
//
//*****************************************************************************
tBoolean
CANRetryGet(unsigned long ulBase)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Read the disable automatic retry setting from the CAN controller.
    //
    if(CANRegRead(ulBase + CAN_O_CTL) & CAN_CTL_DAR)
    {
        //
        // Automatic data retransmission is not enabled.
        //
        return(false);
    }

    //
    // Automatic data retransmission is enabled.
    //
    return(true);
}

//*****************************************************************************
//
//! Reads one of the controller status registers.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param eStatusReg is the status register to read.
//!
//! This function reads a status register of the CAN controller and returns it
//! to the caller.
//! The different status registers are:
//!
//! - \b CAN_STS_CONTROL - the main controller status
//! - \b CAN_STS_TXREQUEST - bit mask of objects pending transmission
//! - \b CAN_STS_NEWDAT - bit mask of objects with new data
//! - \b CAN_STS_MSGVAL - bit mask of objects with valid configuration
//!
//! When reading the main controller status register, a pending status
//! interrupt is cleared.  This parameter should be used in the interrupt
//! handler for the CAN controller if the cause is a status interrupt.  The
//! controller status register fields are as follows:
//!
//! - \b CAN_STATUS_BUS_OFF - controller is in bus-off condition
//! - \b CAN_STATUS_EWARN - an error counter has reached a limit of at least 96
//! - \b CAN_STATUS_EPASS - CAN controller is in the error passive state
//! - \b CAN_STATUS_RXOK - a message was received successfully (independent of
//! any message filtering).
//! - \b CAN_STATUS_TXOK - a message was successfully transmitted
//! - \b CAN_STATUS_LEC_MSK - mask of last error code bits (3 bits)
//! - \b CAN_STATUS_LEC_NONE - no error
//! - \b CAN_STATUS_LEC_STUFF - stuffing error detected
//! - \b CAN_STATUS_LEC_FORM - a format error occurred in the fixed format part
//! of a message
//! - \b CAN_STATUS_LEC_ACK - a transmitted message was not acknowledged
//! - \b CAN_STATUS_LEC_BIT1 - dominant level detected when trying to send in
//! recessive mode
//! - \b CAN_STATUS_LEC_BIT0 - recessive level detected when trying to send in
//! dominant mode
//! - \b CAN_STATUS_LEC_CRC - CRC error in received message
//!
//! The remaining status registers consist of 32-bit-wide bit maps to the
//! message objects. They can be used to quickly obtain information about the
//! status of all the message objects without needing to query each one.  They
//! contain the following information:
//!
//! - \b CAN_STS_TXREQUEST - if a message object's TXRQST bit is set, a
//! transmission is pending on that object.  The application can use this
//! information to determine which objects are still waiting to send a
//! message.
//! - \b CAN_STS_NEWDAT - if a message object's NEWDAT bit is set, a new
//! message has been received in that object, and has not yet been picked up
//! by the host application
//! - \b CAN_STS_MSGVAL - if a message object's MSGVAL bit is set, the object
//! has a valid configuration programmed.  The host application can use this
//! information to determine which message objects are empty/unused.
//!
//! \return Returns the value of the status register.
//
//*****************************************************************************
unsigned long
CANStatusGet(unsigned long ulBase, tCANStsReg eStatusReg)
{
    unsigned long ulStatus;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    switch(eStatusReg)
    {
        //
        // Just return the global CAN status register since that is what was
        // requested.
        //
        case CAN_STS_CONTROL:
        {
            ulStatus = CANRegRead(ulBase + CAN_O_STS);
            CANRegWrite(ulBase + CAN_O_STS,
                        ~(CAN_STS_RXOK | CAN_STS_TXOK | CAN_STS_LEC_M));
            break;
        }

        //
        // Combine the Transmit status bits into one 32bit value.
        //
        case CAN_STS_TXREQUEST:
        {
            ulStatus = CANRegRead(ulBase + CAN_O_TXRQ1);
            ulStatus |= CANRegRead(ulBase + CAN_O_TXRQ2) << 16;
            break;
        }

        //
        // Combine the New Data status bits into one 32bit value.
        //
        case CAN_STS_NEWDAT:
        {
            ulStatus = CANRegRead(ulBase + CAN_O_NWDA1);
            ulStatus |= CANRegRead(ulBase + CAN_O_NWDA2) << 16;
            break;
        }

        //
        // Combine the Message valid status bits into one 32bit value.
        //
        case CAN_STS_MSGVAL:
        {
            ulStatus = CANRegRead(ulBase + CAN_O_MSG1VAL);
            ulStatus |= CANRegRead(ulBase + CAN_O_MSG2VAL) << 16;
            break;
        }

        //
        // Unknown CAN status requested so return 0.
        //
        default:
        {
            ulStatus = 0;
            break;
        }
    }
    return(ulStatus);
}

//*****************************************************************************
//
//! Reads the CAN controller error counter register.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param pulRxCount is a pointer to storage for the receive error counter.
//! \param pulTxCount is a pointer to storage for the transmit error counter.
//!
//! This function reads the error counter register and returns the transmit and
//! receive error counts to the caller along with a flag indicating if the
//! controller receive counter has reached the error passive limit.  The values
//! of the receive and transmit error counters are returned through the
//! pointers provided as parameters.
//!
//! After this call, \e *pulRxCount holds the current receive error count
//! and \e *pulTxCount holds the current transmit error count.
//!
//! \return Returns \b true if the receive error count has reached the error
//! passive limit, and \b false if the error count is below the error passive
//! limit.
//
//*****************************************************************************
tBoolean
CANErrCntrGet(unsigned long ulBase, unsigned long *pulRxCount,
              unsigned long *pulTxCount)
{
    unsigned long ulCANError;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));

    //
    // Read the current count of transmit/receive errors.
    //
    ulCANError = CANRegRead(ulBase + CAN_O_ERR);

    //
    // Extract the error numbers from the register value.
    //
    *pulRxCount = (ulCANError & CAN_ERR_REC_M) >> CAN_ERR_REC_S;
    *pulTxCount = (ulCANError & CAN_ERR_TEC_M) >> CAN_ERR_TEC_S;

    if(ulCANError & CAN_ERR_RP)
    {
        return(true);
    }
    return(false);
}

//*****************************************************************************
//
//! Configures a message object in the CAN controller.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulObjID is the object number to configure (1-32).
//! \param pMsgObject is a pointer to a structure containing message object
//! settings.
//! \param eMsgType indicates the type of message for this object.
//!
//! This function is used to configure any one of the 32 message objects in the
//! CAN controller.  A message object can be configured to be any type of CAN
//! message object as well as to use automatic transmission and reception.
//! This call also allows the message object to be configured to generate
//! interrupts on completion of message receipt or transmission.  The
//! message object can also be configured with a filter/mask so that actions
//! are only taken when a message that meets certain parameters is seen on the
//! CAN bus.
//!
//! The \e eMsgType parameter must be one of the following values:
//!
//! - \b MSG_OBJ_TYPE_TX - CAN transmit message object.
//! - \b MSG_OBJ_TYPE_TX_REMOTE - CAN transmit remote request message object.
//! - \b MSG_OBJ_TYPE_RX - CAN receive message object.
//! - \b MSG_OBJ_TYPE_RX_REMOTE - CAN receive remote request message object.
//! - \b MSG_OBJ_TYPE_RXTX_REMOTE - CAN remote frame receive remote, then
//! transmit message object.
//!
//! The message object pointed to by \e pMsgObject must be populated by the
//! caller, as follows:
//!
//! - \e ulMsgID - contains the message ID, either 11 or 29 bits.
//! - \e ulMsgIDMask - mask of bits from \e ulMsgID that must match if
//! identifier filtering is enabled.
//! - \e ulFlags
//!   - Set \b MSG_OBJ_TX_INT_ENABLE flag to enable interrupt on transmission.
//!   - Set \b MSG_OBJ_RX_INT_ENABLE flag to enable interrupt on receipt.
//!   - Set \b MSG_OBJ_USE_ID_FILTER flag to enable filtering based on the
//!   identifier mask specified by \e ulMsgIDMask.
//! - \e ulMsgLen - the number of bytes in the message data.  This parameter
//! should be non-zero even for a remote frame; it should match the expected
//! bytes of data in the responding data frame.
//! - \e pucMsgData - points to a buffer containing up to 8 bytes of data for a
//! data frame.
//!
//! \b Example: To send a data frame or remote frame (in response to a remote
//! request), take the following steps:
//!
//! -# Set \e eMsgType to \b MSG_OBJ_TYPE_TX.
//! -# Set \e pMsgObject->ulMsgID to the message ID.
//! -# Set \e pMsgObject->ulFlags. Make sure to set \b MSG_OBJ_TX_INT_ENABLE to
//! allow an interrupt to be generated when the message is sent.
//! -# Set \e pMsgObject->ulMsgLen to the number of bytes in the data frame.
//! -# Set \e pMsgObject->pucMsgData to point to an array containing the bytes
//! to send in the message.
//! -# Call this function with \e ulObjID set to one of the 32 object buffers.
//!
//! \b Example: To receive a specific data frame, take the following steps:
//!
//! -# Set \e eMsgObjType to \b MSG_OBJ_TYPE_RX.
//! -# Set \e pMsgObject->ulMsgID to the full message ID, or a partial mask to
//! use partial ID matching.
//! -# Set \e pMsgObject->ulMsgIDMask bits that should be used for masking
//! during comparison.
//! -# Set \e pMsgObject->ulFlags as follows:
//!   - Set \b MSG_OBJ_RX_INT_ENABLE flag to be interrupted when the data frame
//!   is received.
//!   - Set \b MSG_OBJ_USE_ID_FILTER flag to enable identifier-based filtering.
//! -# Set \e pMsgObject->ulMsgLen to the number of bytes in the expected data
//! frame.
//! -# The buffer pointed to by \e pMsgObject->pucMsgData is not used by this
//! call as no data is present at the time of the call.
//! -# Call this function with \e ulObjID set to one of the 32 object buffers.
//!
//! If you specify a message object buffer that already contains a message
//! definition, it is overwritten.
//!
//! \return None.
//
//*****************************************************************************
void
CANMessageSet(unsigned long ulBase, unsigned long ulObjID,
              tCANMsgObject *pMsgObject, tMsgObjType eMsgType)
{
    unsigned short usCmdMaskReg;
    unsigned short usMaskReg0, usMaskReg1;
    unsigned short usArbReg0, usArbReg1;
    unsigned short usMsgCtrl;
    tBoolean bTransferData;
    tBoolean bUseExtendedID;

    bTransferData = 0;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT((ulObjID <= 32) && (ulObjID != 0));
    ASSERT((eMsgType == MSG_OBJ_TYPE_TX) ||
           (eMsgType == MSG_OBJ_TYPE_TX_REMOTE) ||
           (eMsgType == MSG_OBJ_TYPE_RX) ||
           (eMsgType == MSG_OBJ_TYPE_RX_REMOTE) ||
           (eMsgType == MSG_OBJ_TYPE_TX_REMOTE) ||
           (eMsgType == MSG_OBJ_TYPE_RXTX_REMOTE));

    //
    // Wait for busy bit to clear
    //
    while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
    {
    }

    //
    // See if we need to use an extended identifier or not.
    //
    if((pMsgObject->ulMsgID > CAN_MAX_11BIT_MSG_ID) ||
       (pMsgObject->ulFlags & MSG_OBJ_EXTENDED_ID))
    {
        bUseExtendedID = 1;
    }
    else
    {
        bUseExtendedID = 0;
    }

    //
    // This is always a write to the Message object as this call is setting a
    // message object.  This call will also always set all size bits so it sets
    // both data bits.  The call will use the CONTROL register to set control
    // bits so this bit needs to be set as well.
    //
    usCmdMaskReg = (CAN_IF1CMSK_WRNRD | CAN_IF1CMSK_DATAA | CAN_IF1CMSK_DATAB |
                    CAN_IF1CMSK_CONTROL);

    //
    // Initialize the values to a known state before filling them in based on
    // the type of message object that is being configured.
    //
    usArbReg0 = 0;
    usArbReg1 = 0;
    usMsgCtrl = 0;
    usMaskReg0 = 0;
    usMaskReg1 = 0;

    switch(eMsgType)
    {
        //
        // Transmit message object.
        //
        case MSG_OBJ_TYPE_TX:
        {
            //
            // Set the TXRQST bit and the reset the rest of the register.
            //
            usMsgCtrl |= CAN_IF1MCTL_TXRQST;
            usArbReg1 = CAN_IF1ARB2_DIR;
            bTransferData = 1;
            break;
        }

        //
        // Transmit remote request message object
        //
        case MSG_OBJ_TYPE_TX_REMOTE:
        {
            //
            // Set the TXRQST bit and the reset the rest of the register.
            //
            usMsgCtrl |= CAN_IF1MCTL_TXRQST;
            usArbReg1 = 0;
            break;
        }

        //
        // Receive message object.
        //
        case MSG_OBJ_TYPE_RX:
        {
            //
            // This clears the DIR bit along with everything else.  The TXRQST
            // bit was cleared by defaulting usMsgCtrl to 0.
            //
            usArbReg1 = 0;
            break;
        }

        //
        // Receive remote request message object.
        //
        case MSG_OBJ_TYPE_RX_REMOTE:
        {
            //
            // The DIR bit is set to one for remote receivers.  The TXRQST bit
            // was cleared by defaulting usMsgCtrl to 0.
            //
            usArbReg1 = CAN_IF1ARB2_DIR;

            //
            // Set this object so that it only indicates that a remote frame
            // was received and allow for software to handle it by sending back
            // a data frame.
            //
            usMsgCtrl = CAN_IF1MCTL_UMASK;

            //
            // Use the full Identifier by default.
            //
            usMaskReg0 = 0xffff;
            usMaskReg1 = 0x1fff;

            //
            // Make sure to send the mask to the message object.
            //
            usCmdMaskReg |= CAN_IF1CMSK_MASK;
            break;
        }

        //
        // Remote frame receive remote, with auto-transmit message object.
        //
        case MSG_OBJ_TYPE_RXTX_REMOTE:
        {
            //
            // Oddly the DIR bit is set to one for remote receivers.
            //
            usArbReg1 = CAN_IF1ARB2_DIR;

            //
            // Set this object to auto answer if a matching identifier is seen.
            //
            usMsgCtrl = CAN_IF1MCTL_RMTEN | CAN_IF1MCTL_UMASK;

            //
            // The data to be returned needs to be filled in.
            //
            bTransferData = 1;
            break;
        }

        //
        // This case should never happen due to the ASSERT statement at the
        // beginning of this function.
        //
        default:
        {
            return;
        }
    }

    //
    // Configure the Mask Registers.
    //
    if(pMsgObject->ulFlags & MSG_OBJ_USE_ID_FILTER)
    {
        if(bUseExtendedID)
        {
            //
            // Set the 29 bits of Identifier mask that were requested.
            //
            usMaskReg0 = pMsgObject->ulMsgIDMask & CAN_IF1MSK1_IDMSK_M;
            usMaskReg1 = ((pMsgObject->ulMsgIDMask >> 16) &
                            CAN_IF1MSK2_IDMSK_M);
        }
        else
        {
            //
            // Lower 16 bit are unused so set them to zero.
            //
            usMaskReg0 = 0;

            //
            // Put the 11 bit Mask Identifier into the upper bits of the field
            // in the register.
            //
            usMaskReg1 = ((pMsgObject->ulMsgIDMask << 2) &
                            CAN_IF1MSK2_IDMSK_M);
        }
    }

    //
    // If the caller wants to filter on the extended ID bit then set it.
    //
    if((pMsgObject->ulFlags & MSG_OBJ_USE_EXT_FILTER) ==
       MSG_OBJ_USE_EXT_FILTER)
    {
        usMaskReg1 |= CAN_IF1MSK2_MXTD;
    }

    //
    // The caller wants to filter on the message direction field.
    //
    if((pMsgObject->ulFlags & MSG_OBJ_USE_DIR_FILTER) ==
       MSG_OBJ_USE_DIR_FILTER)
    {
        usMaskReg1 |= CAN_IF1MSK2_MDIR;
    }

    if(pMsgObject->ulFlags & (MSG_OBJ_USE_ID_FILTER | MSG_OBJ_USE_DIR_FILTER |
                              MSG_OBJ_USE_EXT_FILTER))
    {
        //
        // Set the UMASK bit to enable using the mask register.
        //
        usMsgCtrl |= CAN_IF1MCTL_UMASK;

        //
        // Set the MASK bit so that this gets transferred to the Message Object.
        //
        usCmdMaskReg |= CAN_IF1CMSK_MASK;
    }

    //
    // Set the Arb bit so that this gets transferred to the Message object.
    //
    usCmdMaskReg |= CAN_IF1CMSK_ARB;

    //
    // Configure the Arbitration registers.
    //
    if(bUseExtendedID)
    {
        //
        // Set the 29 bit version of the Identifier for this message object.
        //
        usArbReg0 |= pMsgObject->ulMsgID & CAN_IF1ARB1_ID_M;
        usArbReg1 |= (pMsgObject->ulMsgID >> 16) & CAN_IF1ARB2_ID_M;

        //
        // Mark the message as valid and set the extended ID bit.
        //
        usArbReg1 |= CAN_IF1ARB2_MSGVAL | CAN_IF1ARB2_XTD;
    }
    else
    {
        //
        // Set the 11 bit version of the Identifier for this message object.
        // The lower 18 bits are set to zero.
        //
        usArbReg1 |= (pMsgObject->ulMsgID << 2) & CAN_IF1ARB2_ID_M;

        //
        // Mark the message as valid.
        //
        usArbReg1 |= CAN_IF1ARB2_MSGVAL;
    }

    //
    // Set the data length since this is set for all transfers.  This is also a
    // single transfer and not a FIFO transfer so set EOB bit.
    //
    usMsgCtrl |= (pMsgObject->ulMsgLen & CAN_IF1MCTL_DLC_M);

    //
    // Mark this as the last entry if this is not the last entry in a FIFO.
    //
    if((pMsgObject->ulFlags & MSG_OBJ_FIFO) == 0)
    {
        usMsgCtrl |= CAN_IF1MCTL_EOB;
    }

    //
    // Enable transmit interrupts if they should be enabled.
    //
    if(pMsgObject->ulFlags & MSG_OBJ_TX_INT_ENABLE)
    {
        usMsgCtrl |= CAN_IF1MCTL_TXIE;
    }

    //
    // Enable receive interrupts if they should be enabled.
    //
    if(pMsgObject->ulFlags & MSG_OBJ_RX_INT_ENABLE)
    {
        usMsgCtrl |= CAN_IF1MCTL_RXIE;
    }

    //
    // Write the data out to the CAN Data registers if needed.
    //
    if(bTransferData)
    {
        CANDataRegWrite(pMsgObject->pucMsgData,
                        (unsigned long *)(ulBase + CAN_O_IF1DA1),
                        pMsgObject->ulMsgLen);
    }

    //
    // Write out the registers to program the message object.
    //
    CANRegWrite(ulBase + CAN_O_IF1CMSK, usCmdMaskReg);
    CANRegWrite(ulBase + CAN_O_IF1MSK1, usMaskReg0);
    CANRegWrite(ulBase + CAN_O_IF1MSK2, usMaskReg1);
    CANRegWrite(ulBase + CAN_O_IF1ARB1, usArbReg0);
    CANRegWrite(ulBase + CAN_O_IF1ARB2, usArbReg1);
    CANRegWrite(ulBase + CAN_O_IF1MCTL, usMsgCtrl);

    //
    // Transfer the message object to the message object specified by ulObjID.
    //
    CANRegWrite(ulBase + CAN_O_IF1CRQ, ulObjID & CAN_IF1CRQ_MNUM_M);
}

//*****************************************************************************
//
//! Reads a CAN message from one of the message object buffers.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulObjID is the object number to read (1-32).
//! \param pMsgObject points to a structure containing message object fields.
//! \param bClrPendingInt indicates whether an associated interrupt should be
//! cleared.
//!
//! This function is used to read the contents of one of the 32 message objects
//! in the CAN controller and return it to the caller.  The data returned is
//! stored in the fields of the caller-supplied structure pointed to by
//! \e pMsgObject.  The data consists of all of the parts of a CAN message,
//! plus some control and status information.
//!
//! Normally, this function is used to read a message object that has received
//! and stored a CAN message with a certain identifier.  However, this function
//! could also be used to read the contents of a message object in order to
//! load the fields of the structure in case only part of the structure must
//! be changed from a previous setting.
//!
//! When using CANMessageGet(), all of the same fields of the structure are
//! populated in the same way as when the CANMessageSet() function is used,
//! with the following exceptions:
//!
//! \e pMsgObject->ulFlags:
//!
//! - \b MSG_OBJ_NEW_DATA indicates if this data is new since the last time it
//! was read
//! - \b MSG_OBJ_DATA_LOST indicates that at least one message was received on
//! this message object and not read by the host before being overwritten.
//!
//! \return None.
//
//*****************************************************************************
void
CANMessageGet(unsigned long ulBase, unsigned long ulObjID,
              tCANMsgObject *pMsgObject, tBoolean bClrPendingInt)
{
    unsigned short usCmdMaskReg;
    unsigned short usMaskReg0, usMaskReg1;
    unsigned short usArbReg0, usArbReg1;
    unsigned short usMsgCtrl;

    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT((ulObjID <= 32) && (ulObjID != 0));

    //
    // This is always a read to the Message object as this call is setting a
    // message object.
    //
    usCmdMaskReg = (CAN_IF1CMSK_DATAA | CAN_IF1CMSK_DATAB |
                    CAN_IF1CMSK_CONTROL | CAN_IF1CMSK_MASK | CAN_IF1CMSK_ARB);

    //
    // Clear a pending interrupt and new data in a message object.
    //
    if(bClrPendingInt)
    {
        usCmdMaskReg |= CAN_IF1CMSK_CLRINTPND;
    }

    //
    // Set up the request for data from the message object.
    //
    CANRegWrite(ulBase + CAN_O_IF2CMSK, usCmdMaskReg);

    //
    // Transfer the message object to the message object specified by ulObjID.
    //
    CANRegWrite(ulBase + CAN_O_IF2CRQ, ulObjID & CAN_IF1CRQ_MNUM_M);

    //
    // Wait for busy bit to clear
    //
    while(CANRegRead(ulBase + CAN_O_IF2CRQ) & CAN_IF1CRQ_BUSY)
    {
    }

    //
    // Read out the IF Registers.
    //
    usMaskReg0 = CANRegRead(ulBase + CAN_O_IF2MSK1);
    usMaskReg1 = CANRegRead(ulBase + CAN_O_IF2MSK2);
    usArbReg0 = CANRegRead(ulBase + CAN_O_IF2ARB1);
    usArbReg1 = CANRegRead(ulBase + CAN_O_IF2ARB2);
    usMsgCtrl = CANRegRead(ulBase + CAN_O_IF2MCTL);

    pMsgObject->ulFlags = MSG_OBJ_NO_FLAGS;

    //
    // Determine if this is a remote frame by checking the TXRQST and DIR bits.
    //
    if((!(usMsgCtrl & CAN_IF1MCTL_TXRQST) && (usArbReg1 & CAN_IF1ARB2_DIR)) ||
       ((usMsgCtrl & CAN_IF1MCTL_TXRQST) && (!(usArbReg1 & CAN_IF1ARB2_DIR))))
    {
        pMsgObject->ulFlags |= MSG_OBJ_REMOTE_FRAME;
    }

    //
    // Get the identifier out of the register, the format depends on size of
    // the mask.
    //
    if(usArbReg1 & CAN_IF1ARB2_XTD)
    {
        //
        // Set the 29 bit version of the Identifier for this message object.
        //
        pMsgObject->ulMsgID = ((usArbReg1 & CAN_IF1ARB2_ID_M) << 16) |
            usArbReg0;

        pMsgObject->ulFlags |= MSG_OBJ_EXTENDED_ID;
    }
    else
    {
        //
        // The Identifier is an 11 bit value.
        //
        pMsgObject->ulMsgID = (usArbReg1 & CAN_IF1ARB2_ID_M) >> 2;
    }

    //
    // Indicate that we lost some data.
    //
    if(usMsgCtrl & CAN_IF1MCTL_MSGLST)
    {
        pMsgObject->ulFlags |= MSG_OBJ_DATA_LOST;
    }

    //
    // Set the flag to indicate if ID masking was used.
    //
    if(usMsgCtrl & CAN_IF1MCTL_UMASK)
    {
        if(usArbReg1 & CAN_IF1ARB2_XTD)
        {
            //
            // The Identifier Mask is assumed to also be a 29 bit value.
            //
            pMsgObject->ulMsgIDMask =
                ((usMaskReg1 & CAN_IF1MSK2_IDMSK_M) << 16) | usMaskReg0;

            //
            // If this is a fully specified Mask and a remote frame then don't
            // set the MSG_OBJ_USE_ID_FILTER because the ID was not really
            // filtered.
            //
            if((pMsgObject->ulMsgIDMask != 0x1fffffff) ||
               ((pMsgObject->ulFlags & MSG_OBJ_REMOTE_FRAME) == 0))
            {
                pMsgObject->ulFlags |= MSG_OBJ_USE_ID_FILTER;
            }
        }
        else
        {
            //
            // The Identifier Mask is assumed to also be an 11 bit value.
            //
            pMsgObject->ulMsgIDMask = ((usMaskReg1 & CAN_IF1MSK2_IDMSK_M) >>
                                       2);

            //
            // If this is a fully specified Mask and a remote frame then don't
            // set the MSG_OBJ_USE_ID_FILTER because the ID was not really
            // filtered.
            //
            if((pMsgObject->ulMsgIDMask != 0x7ff) ||
               ((pMsgObject->ulFlags & MSG_OBJ_REMOTE_FRAME) == 0))
            {
                pMsgObject->ulFlags |= MSG_OBJ_USE_ID_FILTER;
            }
        }

        //
        // Indicate if the extended bit was used in filtering.
        //
        if(usMaskReg1 & CAN_IF1MSK2_MXTD)
        {
            pMsgObject->ulFlags |= MSG_OBJ_USE_EXT_FILTER;
        }

        //
        // Indicate if direction filtering was enabled.
        //
        if(usMaskReg1 & CAN_IF1MSK2_MDIR)
        {
            pMsgObject->ulFlags |= MSG_OBJ_USE_DIR_FILTER;
        }
    }

    //
    // Set the interrupt flags.
    //
    if(usMsgCtrl & CAN_IF1MCTL_TXIE)
    {
        pMsgObject->ulFlags |= MSG_OBJ_TX_INT_ENABLE;
    }
    if(usMsgCtrl & CAN_IF1MCTL_RXIE)
    {
        pMsgObject->ulFlags |= MSG_OBJ_RX_INT_ENABLE;
    }

    //
    // See if there is new data available.
    //
    if(usMsgCtrl & CAN_IF1MCTL_NEWDAT)
    {
        //
        // Get the amount of data needed to be read.
        //
        pMsgObject->ulMsgLen = (usMsgCtrl & CAN_IF1MCTL_DLC_M);

        //
        // Don't read any data for a remote frame, there is nothing valid in
        // that buffer anyway.
        //
        if((pMsgObject->ulFlags & MSG_OBJ_REMOTE_FRAME) == 0)
        {
            //
            // Read out the data from the CAN registers.
            //
            CANDataRegRead(pMsgObject->pucMsgData,
                           (unsigned long *)(ulBase + CAN_O_IF2DA1),
                           pMsgObject->ulMsgLen);
        }

        //
        // Now clear out the new data flag.
        //
        CANRegWrite(ulBase + CAN_O_IF2CMSK, CAN_IF1CMSK_NEWDAT);

        //
        // Transfer the message object to the message object specified by
        // ulObjID.
        //
        CANRegWrite(ulBase + CAN_O_IF2CRQ, ulObjID & CAN_IF1CRQ_MNUM_M);

        //
        // Wait for busy bit to clear
        //
        while(CANRegRead(ulBase + CAN_O_IF2CRQ) & CAN_IF1CRQ_BUSY)
        {
        }

        //
        // Indicate that there is new data in this message.
        //
        pMsgObject->ulFlags |= MSG_OBJ_NEW_DATA;
    }
    else
    {
        //
        // Along with the MSG_OBJ_NEW_DATA not being set the amount of data
        // needs to be set to zero if none was available.
        //
        pMsgObject->ulMsgLen = 0;
    }
}

//*****************************************************************************
//
//! Clears a message object so that it is no longer used.
//!
//! \param ulBase is the base address of the CAN controller.
//! \param ulObjID is the message object number to disable (1-32).
//!
//! This function frees the specified message object from use.  Once a message
//! object has been ``cleared,'' it no longer automatically sends or
//! receives messages, nor does it generate interrupts.
//!
//! \return None.
//
//*****************************************************************************
void
CANMessageClear(unsigned long ulBase, unsigned long ulObjID)
{
    //
    // Check the arguments.
    //
    ASSERT(CANBaseValid(ulBase));
    ASSERT((ulObjID >= 1) && (ulObjID <= 32));

    //
    // Wait for busy bit to clear
    //
    while(CANRegRead(ulBase + CAN_O_IF1CRQ) & CAN_IF1CRQ_BUSY)
    {
    }

    //
    // Clear the message value bit in the arbitration register.  This indicates
    // the message is not valid.
    //
    CANRegWrite(ulBase + CAN_O_IF1CMSK, CAN_IF1CMSK_WRNRD | CAN_IF1CMSK_ARB);
    CANRegWrite(ulBase + CAN_O_IF1ARB1, 0);
    CANRegWrite(ulBase + CAN_O_IF1ARB2, 0);

    //
    // Initiate programming the message object
    //
    CANRegWrite(ulBase + CAN_O_IF1CRQ, ulObjID & CAN_IF1CRQ_MNUM_M);
}

//*****************************************************************************
//
// Close the Doxygen group.
//! @}
//
//*****************************************************************************