SameBoy/Core/joypad.c
2018-02-10 19:50:42 +02:00

64 lines
2.0 KiB
C

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