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/*
Crude VGA Output
Outputs a red and white leaf to VGA. This implementation is crude and noisy,
but a fun demo. It should run most VGA monitors at 640x480, though it does
not follow the timing spec very carefully. Real twisted or shielded wires,
proper grounding, and not doing this on a breadboard are recommended (but
it seems to work ok without).
SerialUSB is disabled to get rid of most interrupts (which mess with timing);
the SysTick is probably the source of the remaining flickers. This means that
you have to use perpetual bootloader or the reset button to flash new
programs.
How to wire this to a VGA port:
D5 via ~200ohms to VGA Red (1)
D6 via ~200ohms to VGA Green (2)
D7 via ~200ohms to VGA Blue (3)
D11 to VGA VSync (14) (swapped?)
D12 to VGA HSync (13) (swapped?)
GND to VGA Ground (5)
GND to VGA Sync Ground (10)
See also:
- http://pinouts.ru/Video/VGA15_pinout.shtml
- http://www.epanorama.net/documents/pc/vga_timing.html
Created 20 July 2010
By Bryan Newbold for LeafLabs
This code is released with no strings attached.
*/
#include "wirish.h"
#define LED_PIN 13
// Pinouts
#define VGA_R 5 // STM32: B6
#define VGA_G 6 // STM32: A8
#define VGA_B 7 // STM32: A9
#define VGA_V 11 // STM32: A6
#define VGA_H 12 // STM32: A7
// These low level macros make GPIO writes much faster
#define VGA_R_HIGH (GPIOB_BASE)->BSRR = BIT(6)
#define VGA_R_LOW (GPIOB_BASE)->BRR = BIT(6)
#define VGA_G_HIGH (GPIOA_BASE)->BSRR = BIT(8)
#define VGA_G_LOW (GPIOA_BASE)->BRR = BIT(8)
#define VGA_B_HIGH (GPIOA_BASE)->BSRR = BIT(9)
#define VGA_B_LOW (GPIOA_BASE)->BRR = BIT(9)
#define VGA_V_HIGH (GPIOA_BASE)->BSRR = BIT(6)
#define VGA_V_LOW (GPIOA_BASE)->BRR = BIT(6)
#define VGA_H_HIGH (GPIOA_BASE)->BSRR = BIT(7)
#define VGA_H_LOW (GPIOA_BASE)->BRR = BIT(7)
void isr_porch(void);
void isr_start(void);
void isr_stop(void);
void isr_update(void);
uint8 toggle;
uint16 x = 0; // X coordinate
uint16 y = 0; // Y coordinate
uint8 v_active = 1; // Are we in the image?
// 1-bit!
uint8 logo[18][16] = {
{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,},
{0,0,0,0,0,0,1,1,1,0,0,0,0,0,0,0,},
{0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,},
{0,0,0,0,1,0,0,1,0,0,1,0,0,0,0,0,},
{0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,0,},
{0,0,1,0,0,0,0,1,0,0,0,0,1,0,0,0,},
{0,0,1,0,0,1,0,1,0,1,0,0,1,0,0,0,},
{0,1,0,0,0,0,1,1,1,0,0,0,0,1,0,0,},
{0,1,0,1,0,0,0,1,0,0,0,1,0,1,0,0,},
{1,0,0,0,1,0,0,1,0,0,1,0,0,0,1,0,},
{1,0,0,0,0,1,0,1,0,1,0,0,0,0,1,0,},
{1,0,0,0,0,0,1,1,1,0,0,0,0,0,1,0,},
{0,1,0,0,0,0,0,1,0,0,0,0,0,1,0,0,},
{0,0,1,1,0,0,0,1,0,0,0,1,1,0,0,0,},
{0,0,0,0,1,1,1,0,1,1,1,0,0,0,0,0,},
{0,0,0,0,0,0,1,0,1,0,0,0,0,0,0,0,},
{0,0,0,0,0,0,1,1,1,0,0,0,0,0,0,0,},
{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,}, };
void setup() {
// Setup our pins
pinMode(LED_PIN, OUTPUT);
pinMode(VGA_R, OUTPUT);
pinMode(VGA_G, OUTPUT);
pinMode(VGA_B, OUTPUT);
pinMode(VGA_V, OUTPUT);
pinMode(VGA_H, OUTPUT);
digitalWrite(VGA_R, LOW);
digitalWrite(VGA_G, LOW);
digitalWrite(VGA_B, LOW);
digitalWrite(VGA_H, HIGH);
digitalWrite(VGA_V, HIGH);
// This gets rid of the majority of the interrupt artifacts;
// a SysTick.end() is required as well
SerialUSB.end();
// Configure
Timer4.pause(); // while we configure
Timer4.setPrescaleFactor(1); // Full speed
Timer4.setChannel1Mode(TIMER_OUTPUTCOMPARE);
Timer4.setChannel2Mode(TIMER_OUTPUTCOMPARE);
Timer4.setChannel3Mode(TIMER_OUTPUTCOMPARE);
Timer4.setChannel4Mode(TIMER_OUTPUTCOMPARE);
Timer4.setOverflow(2287); // Total line time
Timer4.setCompare1(200);
Timer4.attachCompare1Interrupt(isr_porch);
Timer4.setCompare2(300);
Timer4.attachCompare2Interrupt(isr_start);
Timer4.setCompare3(2170);
Timer4.attachCompare3Interrupt(isr_stop);
Timer4.setCompare4(1); // Could be zero I guess
Timer4.attachCompare4Interrupt(isr_update);
Timer4.setCount(0); // Ready...
Timer4.resume(); // Go!
}
void loop() {
toggle ^= 1;
digitalWrite(LED_PIN, toggle);
delay(100);
// Everything happens in the interrupts!
}
// This ISR will end horizontal sync for most of the image and
// setup the vertical sync for higher line counts
void isr_porch(void) {
VGA_H_HIGH;
y++;
// Back to the top
if(y>=523) {
y=1;
v_active = 1;
return;
}
// Other vsync stuff below the image
if(y>=492) {
VGA_V_HIGH;
return;
}
if(y>=490) {
VGA_V_LOW;
return;
}
if(y>=479) {
v_active = 0;
return;
}
}
// This is the main horizontal sweep
void isr_start(void) {
// Skip if we're not in the image at all
if(!v_active) { return; }
// Start Red
VGA_R_LOW;
VGA_R_HIGH;
// For each "pixel" (really 20 or so screen pixels?) go red or white
for(x=0; x<32; x++) {
if(logo[y/28][x/2]) {
VGA_G_HIGH;
VGA_B_HIGH;
} else {
VGA_G_LOW;
VGA_B_LOW;
}
}
}
// End of the horizontal line
void isr_stop(void) {
if(!v_active) { return; }
VGA_R_LOW;
VGA_G_LOW;
VGA_B_LOW;
}
// Setup horizonal sync
void isr_update(void) {
VGA_H_LOW;
}
int main(void) {
init();
setup();
while (1) {
loop();
}
return 0;
}
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