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Sandro authored and Sandro committed Apr 21, 2015
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485 changes: 485 additions & 0 deletions README.md

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271 changes: 271 additions & 0 deletions VGAX.cpp
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#include "VGAX.h"

//HSYNC pin used by TIMER2
#define HSYNCPIN 3

//These two pin cannot be modified without modify the HSYNC assembler code
#define COLORPIN0 6
#define COLORPIN1 7

//VSYNC pin used by TIMER1. Can be 9 or 10
#define VSYNCPIN 9

//Number of VGA lines to be skipped (black lines)
/*These lines includes the vertical sync pulse and back porch.
Minimum value must be 35 (calculate from Nick Gammon)
You can modify this value to center the framebuffer vertically, or not*/
#define SKIPLINES 90

//number of visible lines, after SKIPLINES
#define RENDERLCOUNT 359

static byte afreq, afreq0;
unsigned vtimer;
static byte aline, rlinecnt;
static byte vskip;
byte vgaxfb[VGAX_HEIGHT*VGAX_BWIDTH];

//VSYNC interrupt
ISR(TIMER1_OVF_vect) {
aline=-1;
vskip=SKIPLINES;
vtimer++;
rlinecnt=0;
}
//HSYNC interrupt
ISR(TIMER2_OVF_vect) {
/*
NOTE: I prefer to generate the line here, inside the interrupt.
Gammon's code generate the line pixels inside main().
My versin generate the signal using only interrupts, so inside main() function
you can do anything you want. Your code will be interrupted when VGA signal
needs to be generated
*/
//generate audio modulation. around 15 clocks
asm volatile( //4c to load Z and Y
" ld r16, Z \n\t" //c1 r16=afreq
" cpi %[freq0], 0 \n\t" //c1 afreq0==0 ?
" breq no_audio \n\t" //c1/2 *0
"play_audio: \n\t"
" cpi r16, 0 \n\t" //c1 afreq==0 ?
" brne dont_flip_audio_pin \n\t" //c1/2 *1
"flip_audio_pin: \n\t"
" ldi r18, 1 \n\t" //c1
" out %[audiopin], r18 \n\t" //c1
" st Z, %[freq0] \n\t" //c1 afreq=afreq0
" rjmp end \n\t" //c2
//" mov r16, %[freq0]\n\r"
//" dec r16\n\r"
"no_audio: \n\t"
" nop \n\t" //c1
" nop \n\t" //c1
" nop \n\t" //c1
//" nop \n\t" //c1
" nop \n\t" //c1
" nop \n\t" //c1
" nop \n\t" //c1
" rjmp end \n\t" //c2
"dont_flip_audio_pin: \n\t"
" dec r16 \n\t" //c1
" st Z, r16 \n\t" //c1
//" nop \n\t" //c1
"end: \n\t"
:
: "z" (&afreq),
[freq0] "r" (afreq0),
[audiopin] "i" _SFR_IO_ADDR(PINC)
: "r16", "r18");

//check vertical porch
if (vskip) {
vskip--;
return;
}
if (rlinecnt<60) {
//interrupt jitter fix (needed to keep signal stable)
//code from https://github.com/cnlohr/avrcraft/tree/master/terminal
//modified from 4 nop align to 8 nop align
#define DEJITTER_OFFSET 1
#define DEJITTER_SYNC -3
asm volatile(
" lds r16, %[timer0] \n\t" //
//" add r16, %[toffset] \n\t" //
" subi r16, %[tsync] \n\t" //
" andi r16, 7 \n\t" //
" call TL \n\t" //
"TL: \n\t" //
" pop r31 \n\t" //
" pop r30 \n\t" //
" adiw r30, (LW-TL-5) \n\t" //
" add r30, r16 \n\t" //
//" adc r31, __zero_reg__ \n\t" //
" ijmp \n\t" //
"LW: \n\t" //
" nop \n\t" //
" nop \n\t" //
" nop \n\t" //
" nop \n\t" //
" nop \n\t" //
" nop \n\t" //
" nop \n\t" //
//" nop \n\t" //
"LBEND: \n\t" //
:
: [timer0] "i" (&TCNT0),
[toffset] "i" ((uint8_t)DEJITTER_OFFSET),
[tsync] "i" ((uint8_t)DEJITTER_SYNC)
: "r30", "r31", "r16", "r17");
/*
Output all pixels.
NOTE: My trick here is to unpack 4 pixels and shift them before writing to
PORTD.
Pixels are packed as 0b11223344 because the first pixel write have no time
to perform a shift (ld, out) and must be prealigned to the two upper bits
of PORTD, where the two wires of the VGA DSUB are connected. The second,
the third and the forth pixels are shifted left using mul opcode instead
of a left shift opcode. Shift opcodes are slow and can shift only 1 bit at
a time, using 1 clock cycle. mul is faster.
Instead of using a loop i use the .rept assembler directive to generate an
unrolled loop of 30 iterations.
*/
asm volatile (
" ldi r20, 4 \n\t" //const for <<2bit
#ifdef VGAX_DEV_DEPRECATED
".rept 14 \n\t" //center line
" nop \n\t" //
".endr \n\t" //
#endif
".rept 30 \n\t" //output 4 pixels for each iteration
" ld r16, Z+ \n\t" //
" out %[port], r16 \n\t" //write pixel 1
" mul r16, r20 \n\t" //<<2
" out %[port], r0 \n\t" //write pixel 2
" mul r0, r20 \n\t" //<<4
" out %[port], r0 \n\t" //write pixel 3
" mul r0, r20 \n\t" //<<6
" out %[port], r0 \n\t" //write pixel 6
".endr \n\t" //
" nop \n\t" //expand last pixel
" ldi r16, 0 \n\t" //
" out %[port], r16 \n\t" //write black for next pixels
:
: [port] "I" (_SFR_IO_ADDR(PORTD)),
"z" "I" (/*rline*/(byte*)vgaxfb + rlinecnt*VGAX_BWIDTH)
: "r16", "r17", "r20", "r21", "memory");

//increment framebuffer line counter after 6 VGA lines
if (++aline==5) {
aline=-1;
rlinecnt++;
} else {
#ifdef VGAX_DEV_DEPRECATED
//small delay to keep the line signal aligned
asm volatile(
".rept 17 \n\t" //
" nop \n\t" //
".endr \n\t" //
:::);
#endif
}
}
}
void VGAX::begin(bool enableTone) {
//Timers setup code, modified version of the Nick Gammon's VGA sketch
cli();
//setup audio pin
if (enableTone) {
pinMode(A0, OUTPUT);
}
//disable TIMER0 interrupt
TIMSK0=0;
TCCR0A=0;
TCCR0B=1; //enable 16MHz counter (used to fix the HSYNC interrupt jitter)
OCR0A=0;
OCR0B=0;
TCNT0=0;
//TIMER1 - vertical sync pulses
pinMode(VSYNCPIN, OUTPUT);
#if VSYNCPIN==10
TCCR1A=bit(WGM10) | bit(WGM11) | bit(COM1B1);
TCCR1B=bit(WGM12) | bit(WGM13) | bit(CS12) | bit(CS10); //1024 prescaler
OCR1A=259; //16666 / 64 uS=260 (less one)
OCR1B=0; //64 / 64 uS=1 (less one)
TIFR1=bit(TOV1); //clear overflow flag
TIMSK1=bit(TOIE1); //interrupt on overflow on TIMER1
#else
TCCR1A=bit(WGM11) | bit(COM1A1);
TCCR1B=bit(WGM12) | bit(WGM13) | bit(CS12) | bit(CS10); //1024 prescaler
ICR1=259; //16666 / 64 uS=260 (less one)
OCR1A=0; //64 / 64 uS=1 (less one)
TIFR1=bit(TOV1); //clear overflow flag
TIMSK1=bit(TOIE1); //interrupt on overflow on TIMER1
#endif
//TIMER2 - horizontal sync pulses
pinMode(HSYNCPIN, OUTPUT);
TCCR2A=bit(WGM20) | bit(WGM21) | bit(COM2B1); //pin3=COM2B1
TCCR2B=bit(WGM22) | bit(CS21); //8 prescaler
OCR2A=63; //32 / 0.5 uS=64 (less one)
OCR2B=7; //4 / 0.5 uS=8 (less one)
TIFR2=bit(TOV2); //clear overflow flag
TIMSK2=bit(TOIE2); //interrupt on overflow on TIMER2
//pins for outputting the colour information
pinMode(COLORPIN0, OUTPUT);
pinMode(COLORPIN1, OUTPUT);
sei();
}
void VGAX::end() {
//disable TIMER0
TCCR0A=0;
TCCR0B=0;
//disable TIMER1
TCCR1A=0;
TCCR1B=0;
//disable TIMER2
TCCR2A=0;
TCCR2B=0;
}
void VGAX::clear(byte color) {
register byte c=color;
c&=3;
register byte c0=(c*4) | c;
c0|=c0*16;
unsigned cnt=VGAX_BSIZE;
byte *o=(byte*)vgaxfb;
while (cnt--)
*o++=c0;
}
void VGAX::copy(byte *src) {
byte *o=(byte*)vgaxfb;
unsigned cnt=VGAX_BSIZE;
while (cnt--)
*o++=pgm_read_byte(src++);
}
void VGAX::fillrect(byte x, byte y, byte width, byte height, byte color) {
byte rh=height;
while (rh--) {
byte rw=width, rx=x;
while (rw--) {
putpixel(rx, y, color);
rx++;
}
y++;
}
}
void VGAX::tone(unsigned int frequency) {
//HSYNC=32usec
afreq=1000000 / frequency / 2 / 32;
afreq0=afreq;
}
void VGAX::noTone() {
afreq0=0;
}
void VGAX::delay(int msec) {
while (msec--) {
unsigned cnt=16000/32;
while (cnt--)
asm volatile("nop\nnop\nnop\nnop\n");
}
}
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