diff --git a/Core/gb.h b/Core/gb.h index 97c7dd4..a422d5e 100644 --- a/Core/gb.h +++ b/Core/gb.h @@ -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 */ diff --git a/Core/sgb.c b/Core/sgb.c index 9dce2d8..71fccfe 100644 --- a/Core/sgb.c +++ b/Core/sgb.c @@ -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; }