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Something more to think about when attempting to transfer a BC value
from the device to the host within each DMA data burst...
The BC values needs to be transmitted at the end of the DMA burst
around the same time the CRC is transmitted. This is because the BC
for the current DMA burst is not known until the end of the DMA
burst. This is because the host or device are able to terminate DMA
bursts at any time (for any reason). For example, the device might
want to transfer a 1000 bytes, the host might stop the transfer after
only 50 bytes. {This is much different that PIO bursts. In PIO the BC
value is the number of bytes the host SHALL transfer for the current
DRQ data block.} For this new DMA BC to be valid the device can not
send it to the host until the end of the DMA burst. And to have the
same effect as the PIO BC this new DMA BC must be sent from the
device to the host for both read and write DMA transfers.
Comments?
*** Hale Landis *** www.ata-atapi.com ***
