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Handle the SGB header commands, disable SGB functions if needed.

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This commit is contained in:
Lior Halphon 2018-11-11 22:50:00 +02:00
parent 44891d5c4a
commit 5c581651ce
2 changed files with 36 additions and 5 deletions
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1
Core/gb.h
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@ -473,6 +473,7 @@ struct GB_gameboy_internal_s {
uint8_t sgb_command_write_index;
bool sgb_ready_for_pulse;
bool sgb_ready_for_write;
bool sgb_disable_commands;
);
/* Unsaved data. This includes all pointers, as well as everything that shouldn't be on a save state */

40
Core/sgb.c
View File

@ -1,8 +1,42 @@
#include "sgb.h"
static void command_ready(GB_gameboy_t *gb)
{
/* SGB header commands are used to send the contents of the header to the SNES CPU.
A header command looks like this:
Command ID: 0b1111xxx1, where xxx is the packet index. (e.g. F1 for [0x104, 0x112), F3 for [0x112, 0x120))
Checksum: Simple one byte sum for the following content bytes
0xE content bytes. The last command, FB, is padded with zeros, so information past the header is not sent. */
if (gb->sgb_command[0] >= 0xF0) {
uint8_t checksum = 0;
for (unsigned i = 2; i < 0x10; i++) {
checksum += gb->sgb_command[i];
}
if (checksum != gb->sgb_command[1]) {
GB_log(gb, "Failed checksum for SGB header command, disabling SGB features\n");
gb->sgb_disable_commands = true;
return;
}
}
if (gb->sgb_command[0] == 0xf9) {
if (gb->sgb_command[0xc] != 3) { // SGB Flag
GB_log(gb, "SGB flag is not 0x03, disabling SGB features\n");
gb->sgb_disable_commands = true;
}
}
else if (gb->sgb_command[0] == 0xfb) {
if (gb->sgb_command[0x3] != 0x33) { // Old licensee code
GB_log(gb, "Old licensee code is not 0x33, disabling SGB features\n");
gb->sgb_disable_commands = true;
}
}
}
void GB_sgb_write(GB_gameboy_t *gb, uint8_t value)
{
if (!GB_is_sgb(gb)) return;
if (gb->sgb_disable_commands) return;
switch ((value >> 4) & 3 ) {
case 3:
gb->sgb_ready_for_pulse = true;
@ -11,11 +45,7 @@ void GB_sgb_write(GB_gameboy_t *gb, uint8_t value)
case 2: // Zero
if (!gb->sgb_ready_for_pulse || !gb->sgb_ready_for_write) return;
if (gb->sgb_command_write_index >= sizeof(gb->sgb_command) * 8) {
GB_log(gb, "Got SGB command: ");
for (unsigned i = 0; i < 16; i++) {
GB_log(gb, "%02x ", gb->sgb_command[i]);
}
GB_log(gb, "\n");
command_ready(gb);
gb->sgb_ready_for_pulse = false;
gb->sgb_ready_for_write = false;
}