void OPL_WriteRegister(int reg, int value) { int i; OPL_WritePort(OPL_REGISTER_PORT, reg); // For timing, read the register port six times after writing the // register number to cause the appropriate delay for (i=0; i<6; ++i) { // An oddity of the Doom OPL code: at startup initialization, // the spacing here is performed by reading from the register // port; after initialization, the data port is read, instead. if (init_stage_reg_writes) { OPL_ReadPort(OPL_REGISTER_PORT); } else { OPL_ReadPort(OPL_DATA_PORT); } } OPL_WritePort(OPL_DATA_PORT, value); // Read the register port 24 times after writing the value to // cause the appropriate delay for (i=0; i<24; ++i) { OPL_ReadStatus(); } }
int OPL_Detect(void) { int result1, result2; int i; // Reset both timers: OPL_WriteRegister(OPL_REG_TIMER_CTRL, 0x60); // Enable interrupts: OPL_WriteRegister(OPL_REG_TIMER_CTRL, 0x80); // Read status result1 = OPL_ReadStatus(); // Set timer: OPL_WriteRegister(OPL_REG_TIMER1, 0xff); // Start timer 1: OPL_WriteRegister(OPL_REG_TIMER_CTRL, 0x21); // Wait for 80 microseconds // This is how Doom does it: for (i=0; i<200; ++i) { OPL_ReadStatus(); } OPL_Delay(1 * OPL_MS); // Read status result2 = OPL_ReadStatus(); // Reset both timers: OPL_WriteRegister(OPL_REG_TIMER_CTRL, 0x60); // Enable interrupts: OPL_WriteRegister(OPL_REG_TIMER_CTRL, 0x80); return (result1 & 0xe0) == 0x00 && (result2 & 0xe0) == 0xc0; }