63 lines
1.9 KiB
C
63 lines
1.9 KiB
C
#include <stdio.h>
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#include "gb.h"
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#include <assert.h>
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void GB_update_joyp(GB_gameboy_t *gb)
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{
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uint8_t key_selection = 0;
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uint8_t previous_state = 0;
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/* Todo: add delay to key selection */
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previous_state = gb->io_registers[GB_IO_JOYP] & 0xF;
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key_selection = (gb->io_registers[GB_IO_JOYP] >> 4) & 3;
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gb->io_registers[GB_IO_JOYP] &= 0xF0;
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switch (key_selection) {
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case 3:
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/* Nothing is wired, all up */
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gb->io_registers[GB_IO_JOYP] |= 0x0F;
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break;
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case 2:
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/* Direction keys */
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for (uint8_t i = 0; i < 4; i++) {
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gb->io_registers[GB_IO_JOYP] |= (!gb->keys[i]) << i;
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}
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/* Forbid pressing two opposing keys, this breaks a lot of games; even if it's somewhat possible. */
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if (!(gb->io_registers[GB_IO_JOYP] & 1)) {
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gb->io_registers[GB_IO_JOYP] |= 2;
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}
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if (!(gb->io_registers[GB_IO_JOYP] & 4)) {
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gb->io_registers[GB_IO_JOYP] |= 8;
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}
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break;
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case 1:
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/* Other keys */
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for (uint8_t i = 0; i < 4; i++) {
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gb->io_registers[GB_IO_JOYP] |= (!gb->keys[i + 4]) << i;
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}
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break;
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case 0:
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for (uint8_t i = 0; i < 4; i++) {
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gb->io_registers[GB_IO_JOYP] |= (!(gb->keys[i] || gb->keys[i + 4])) << i;
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}
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break;
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default:
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break;
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}
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if (previous_state != (gb->io_registers[GB_IO_JOYP] & 0xF)) {
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/* The joypad interrupt DOES occur on CGB (Tested on CGB-CPU-06), unlike what some documents say. */
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gb->io_registers[GB_IO_IF] |= 0x10;
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gb->stopped = false;
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}
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gb->io_registers[GB_IO_JOYP] |= 0xC0; // No SGB support
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}
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void GB_set_key_state(GB_gameboy_t *gb, GB_key_t index, bool pressed)
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{
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assert(index >= 0 && index < GB_KEY_MAX);
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gb->keys[index] = pressed;
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}
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