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Hi guys !
Recently, I have been trying to enable PCI DMA for ATAPI drives. my DMA code works well on ATA, and PIO works well on ATA & ATAPI. but when i try to use DMA Protocol with ATAPI, it ends with an error. Status Byte 0x1F7 is 0x51, and Error Byte is 0x50, this should mean that a SCSI error have happened, and this error is one of these:

MEDIUM ERROR - UNRECOVERED READ ERROR
MEDIUM ERROR - ADDRESS MARK NOT FOUND FOR ID FIELD (What do these heavy words mean????)
MEDIUM ERROR - RECORD NOT FOUND
MEDIUM ERROR - LOGICAL BLOCK ADDRESS OUT OF RANGE

I use the same 6-word packet and send it, then do a PIO transfer, and it works well.. why ATAPI DMA is problematic??
Any one has any idea plz?? I followed up these well done articles on the wiki but really the problem still exists... any help would be appreciated...

Thanks in advance and regards!

Error Byte is 0x50

Sense Key 5 = ILLEGAL REQUEST

You should send a "REQUEST SENSE" packet command to the drive to get the ASC (Additional Sense Code) and ASQ. Those values might help you find the problem.

I had already resolved the problem but thanks also for your help .

As you said, it was an illegal request, as when i checked VMWare log, i found this: "CD-ROM: Unknown Command 0xA8". Although this command "READ(12)" works well in PIO Mode, but i think VMWare doesn't accept it in DMA (I don't know why). When i use "READ (10)", it works well on both PIO and DMA!

Thankx and regards...