public virtual void WritePort(byte port, byte data)
{
if (BitUtilities.IsBitSet(data, 7))
{
/* LATCH/DATA byte; get channel (0-3) and type (0 is tone/noise, 1 is volume) */
latchedChannel = (byte)((data >> 5) & 0x03);
latchedType = (byte)((data >> 4) & 0x01);
/* Mask off non-data bits */
data &= 0x0F;
/* If target is channel 3 noise (3 bits), mask off highest bit */
if (latchedChannel == 3 && latchedType == 0)
{
data &= 0x07;
}
/* Write to register */
if (latchedType == 0)
{
/* Data is tone/noise */
toneRegisters[latchedChannel] = (ushort)((toneRegisters[latchedChannel] & 0x03F0) | data);
}
else
{
/* Data is volume */
volumeRegisters[latchedChannel] = data;
}
}
else
{
/* DATA byte; mask off non-data bits */
data &= 0x3F;
/* Write to register */
if (latchedType == 0)
{
/* Data is tone/noise */
if (latchedChannel == 3)
{
/* Target is channel 3 noise, mask off excess bits and write to low bits of register */
toneRegisters[latchedChannel] = (ushort)(data & 0x07);
}
else
{
/* Target is not channel 3 noise, write to high bits of register */
toneRegisters[latchedChannel] = (ushort)((toneRegisters[latchedChannel] & 0x000F) | (data << 4));
}
}
else
{
/* Data is volume; mask off excess bits and write to low bits of register */
volumeRegisters[latchedChannel] = (ushort)(data & 0x0F);
}
}
}
