Reading a track:

Select drive, enable controller and motor but turn DMAGATE off.
Reset transcopy board (turn GO on and off)
Set read clock (ports 4, 5 and 1)
Turn on RDENBL
Set up DMA
Wait for index to go high
Wait for index to go low
Turn on GO and RDENBL
Enable DMA
Wait for index to go high
Read DMA word count to get track length -index
Wait for index to go low
Read DMA word count to get entire track length
Wait for DMA to finish
Disable (mask) DMA
Turn off GO and RDENBL
Deselect head
Turn DMAGATE on
