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/*
VGA video generation
Author: Nick Gammon
Date: 20th April 2012
Example code without I2C communications.
Connections:
D1 : Pixel output (180 ohms in series) (connect to R, G, B tied together) --> Pins 1, 2, 3 on DB15 socket
D3 : Horizontal Sync (68 ohms in series) --> Pin 13 on DB15 socket
D10 : Vertical Sync (68 ohms in series) --> Pin 14 on DB15 socket
Gnd : --> Pins 5, 6, 7, 8, 10 on DB15 socket
*/
#include "TimerHelpers.h"
#include <avr/pgmspace.h>
#include "screenFont.h"
#include <avr/sleep.h>
#define BETA_ARDUINO ARDUINO < 100
const byte pixelPin = 1; // <------- Pixel data
const byte hSyncPin = 3; // <------- HSYNC
const byte MSPIM_SCK = 4; // <-- we aren't using it directly
const byte vSyncPin = 10; // <------- VSYNC
const int horizontalBytes = 20; // 160 pixels wide
const int verticalPixels = 480; // 480 pixels high
const byte i2cAddress = 42;
// Timer 1 - Vertical sync
// output OC1B pin 16 (D10) <------- VSYNC
// Period: 16.64 mS (60 Hz)
// 1/60 * 1e6 = 16666.66 uS
// Pulse for 64 uS (2 x HSync width of 32 uS)
// Sync pulse: 2 lines
// Back porch: 33 lines
// Active video: 480 lines
// Front porch: 10 lines
// Total: 525 lines
// Timer 2 - Horizontal sync
// output OC2B pin 5 (D3) <------- HSYNC
// Period: 32 uS (31.25 kHz)
// (1/60) / 525 * 1e6 = 31.74 uS
// Pulse for 4 uS (96 times 39.68 nS)
// Sync pulse: 96 pixels
// Back porch: 48 pixels
// Active video: 640 pixels
// Front porch: 16 pixels
// Total: 800 pixels
// Pixel time = ((1/60) / 525 * 1e9) / 800 = 39.68 nS
// frequency = 1 / (((1/60) / 525 * 1e6) / 800) = 25.2 MHz
// However in practice, it is the SPI speed, namely a period of 125 nS
// (that is 2 x system clock speed)
// giving an 8 MHz pixel frequency. Thus the characters are about 3 times too wide.
// Thus we fit 160 of "our" pixels on the screen in what usually takes 3 x 160 = 480
const byte screenFontHeight = 8;
const byte screenFontWidth = 8;
const int verticalLines = verticalPixels / screenFontHeight / 2; // double-height characters
const int horizontalPixels = horizontalBytes * screenFontWidth;
const byte verticalBackPorchLines = 35; // includes sync pulse?
const int verticalFrontPorchLines = 525 - verticalBackPorchLines;
volatile int vLine;
volatile int messageLine;
volatile byte backPorchLinesToGo;
char message [verticalLines] [horizontalBytes];
// ISR: Vsync pulse
ISR (TIMER1_OVF_vect)
{
vLine = 0;
messageLine = 0;
backPorchLinesToGo = verticalBackPorchLines;
} // end of TIMER1_OVF_vect
// ISR: Hsync pulse ... this interrupt merely wakes us up
ISR (TIMER2_OVF_vect)
{
} // end of TIMER2_OVF_vect
void setup()
{
// initial message ... change to suit
for (int i = 0; i < verticalLines; i++)
sprintf (message [i], "Line %03i - hello!", i);
// disable Timer 0
TIMSK0 = 0; // no interrupts on Timer 0
OCR0A = 0; // and turn it off
OCR0B = 0;
// Timer 1 - vertical sync pulses
pinMode (vSyncPin, OUTPUT);
Timer1::setMode (15, Timer1::PRESCALE_1024, Timer1::CLEAR_B_ON_COMPARE);
OCR1A = 259; // 16666 / 64 uS = 260 (less one)
OCR1B = 0; // 64 / 64 uS = 1 (less one)
TIFR1 = _BV (TOV1); // clear overflow flag
TIMSK1 = _BV (TOIE1); // interrupt on overflow on timer 1
// Timer 2 - horizontal sync pulses
pinMode (hSyncPin, OUTPUT);
Timer2::setMode (7, Timer2::PRESCALE_8, Timer2::CLEAR_B_ON_COMPARE);
OCR2A = 63; // 32 / 0.5 uS = 64 (less one)
OCR2B = 7; // 4 / 0.5 uS = 8 (less one)
TIFR2 = _BV (TOV2); // clear overflow flag
TIMSK2 = _BV (TOIE2); // interrupt on overflow on timer 2
// Set up USART in SPI mode (MSPIM)
// baud rate must be zero before enabling the transmitter
UBRR0 = 0; // USART Baud Rate Register
pinMode (MSPIM_SCK, OUTPUT); // set XCK pin as output to enable master mode
UCSR0B = 0;
UCSR0C = _BV (UMSEL00) | _BV (UMSEL01) | _BV (UCPHA0) | _BV (UCPOL0); // Master SPI mode
// prepare to sleep between horizontal sync pulses
set_sleep_mode (SLEEP_MODE_IDLE);
} // end of setup
// draw a single scan line
void doOneScanLine ()
{
// after vsync we do the back porch
if (backPorchLinesToGo)
{
backPorchLinesToGo--;
return;
} // end still doing back porch
// if all lines done, do the front porch
if (vLine >= verticalPixels)
return;
// pre-load pointer for speed
const register byte * linePtr = &screen_font [ (vLine >> 1) & 0x07 ] [0];
register char * messagePtr = & (message [messageLine] [0] );
// how many pixels to send
register byte i = horizontalBytes;
// turn transmitter on
UCSR0B = _BV (TXEN0); // transmit enable (starts transmitting white)
// blit pixel data to screen
while (i--)
UDR0 = pgm_read_byte (linePtr + (* messagePtr++));
// wait till done
while (!(UCSR0A & _BV(TXC0)))
{}
// disable transmit
UCSR0B = 0; // drop back to black
// this line done
vLine++;
// every 16 pixels it is time to move to a new line in our text
// (because we double up the characters vertically)
if ((vLine & 0xF) == 0)
messageLine++;
} // end of doOneScanLine
void loop()
{
// sleep to ensure we start up in a predictable way
sleep_mode ();
doOneScanLine ();
} // end of loop
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