92 lines
2.0 KiB
C
92 lines
2.0 KiB
C
/**
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* @file main.c
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* @author giomba@glgprograms.it
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* @brief OSDY main.
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*
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* @copyright Copyright RetrOfficina GLG Programs (c) 2022
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*
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* Video image generator superimposition for analog PAL signals,
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* with Atmega328, for your retro OSD titles.
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*
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*/
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#include "const.h"
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#include <avr/interrupt.h>
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#include <avr/io.h>
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#include <string.h>
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volatile uint16_t frame = 0;
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volatile uint16_t line = 0xfe;
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volatile uint8_t image = 0xff;
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// horizontal and vertical position
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// (and current increments)
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// of bouncing sprite
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volatile uint8_t vpos = 0;
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volatile uint16_t hpos = 0;
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volatile int8_t vinc = +1;
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volatile int8_t hinc = +1;
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// vertical sync interrupt
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void int_vertical_sync_s(void);
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ISR(INT0_vect) {
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// count frames
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frame += 1;
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// move sprite
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vpos += vinc;
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hpos += hinc;
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// invert bouncing direction
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if (vpos == 0)
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vinc = +1;
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if (vpos == FRAME_LINE_HEIGHT - SPRITE_LINE_HEIGHT)
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vinc = -1;
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if (hpos == BACK_PORCH_SYSCLOCK_OFFSET)
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hinc = +1;
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if (hpos == FRAME_SYSCLOCK_WIDTH - SPRITE_SYSCLOCK_WIDTH -
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FRONT_PORCH_SYSCLOCK_OFFSET - HSYNC_SYSCLOCK_TUNE)
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hinc = -1;
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int_vertical_sync_s();
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}
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// horizontal sync interrupt
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void int_horizontal_sync_s(void);
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ISR(INT1_vect) {
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// count lines
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line += 1;
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// we are past the last line of the sprite
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if (line >= vpos + SPRITE_LINE_HEIGHT)
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return;
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if (line >= vpos)
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int_horizontal_sync_s();
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}
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ISR(TIMER1_COMPA_vect, ISR_NAKED) {
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// end-of back porch timer interrupt
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asm("jmp int_timer_1");
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}
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// external assembly main loop
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void main_asm(void);
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int main() {
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// port B, pin 4 and 5 as output, others as input
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DDRB |= 0x30;
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// set interrupt vectors at address 0x0, not bootloader
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// timing is important, see atmel datasheet
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_SFR_IO8(MCUCR) = (1 << IVCE);
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_SFR_IO8(MCUCR) = 0;
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EICRA = 0x0a; // external interrupt 0 and 1, falling edge
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EIMSK = 0x03; // external interrupt 0 and 1, mask enable
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TCCR1A = 0x00; // don't connect output pins to timer, CTC[1:0] mode
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TCCR1B = 0x09; // CTC[3:2] mode, no prescaler
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main_asm();
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}
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