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;
}