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kepler said: > This message is from the T13 list server. > All commands which use Data register for data transfer use only DD[7:0] > in 8-bit PIO transfer mode. Correct. Remember that only CF devices support 8-bit PIO data transfer. In general other ATA/ATAPI devices that are not CF do not implement 8-bit PIO data transfer mode. > DMA commands use the 16-bit Data port to transfer data. for devices not > implemented with PACKET feature set. All ATA and ATAPI (and CF) devices use the 16-bit Data Port to perform DMA transfers (Multiword DMA or UltraDMA). > I want to make sure that whether DMA commands should be accepted or > aborted in CFA devices with 8-bit PIO data transfer mode enabled. > According to section 6.2.1.15 on page 130 of "CF+ and CompactFlash > Specification Revision 3.0", it mentinos that "When a Read DMA command > is received by the Card and 8 bit transfer mode has been enabled by the > Set Features command, the Card shall return the Aborted error". This is correct - And I was incorrect in a previous email when I said that DMA commands were 'legal' when a CF device was in 8-bit PIO data transfer mode. > I think the PIO Word Data Register and DMA Word Data Register described > on page 99 of CFA3.0 spe. correspond to Data Port and Data register > described on page 65 of ATA/ATAPI-6, respectively. Correct. > The architecture > between CFA and ATA devices are pretty similar. A CF device in TrueIDE mode is exactly identical to any ATA/ATAPI-x hard disk drive device. In fact some CF devices really are hard disk drives (and not flash memory devices that look like a hard disk drive). A CF device has all the same ATA registers, the same ATA command protocols and mostly the same ATA command set (R/W SECTORS/MULTIPLE/DMA, SET FEATURES, IDENTIFY, etc). > The purpose of 8-bit > data transfer mode is for the compatibility of old host controllers > which have only 8-bit data bus width to access devices. CF device have an 8-bit data transfer mode because a CF device is really a PCMCIA PC Card ATA device and when a CF is operating in a PCMCIA interface mode it must support 8-bit data transfers. This same feature was included in the CF TrueIDE mode but has rarely been used. There is much history here going back 15 years that I will not include in this email. > ATA/ATAPI-6 specficiation does not have the specific descriptions for > the handling of DMA commands in 8-bit mode for devices supporting the > CFA feature set, but CFA 3.0 specification does abort DMA commands in > 8-bit mode. Remember that for CF devices the CFA specification 'overrides' the ATA/ATAPI-x standards. CF devices must conform to the CF specification in other to qualify to use the CFA's CF logo. Of course we would all like the ATA/ATAPI-x and CF documents to be in agreement but that is difficult given that the documents are generated by different organizations with little overlap in membership. > Is DMA READ command aborted or DD[15:0] bus used for data transfer when > the ATA device receives the DMA READ command with CFA 8-bit transfer > mode enabled? The ATA device you describe would need to be a CF device operating in TrueIDE mode. In this case, and to conform with the CF specification, the device would abort the DMA command when the device was in 8-bit PIO data transfer mode. It is unlikely that you will find any ATA devices (other than CF devices) that implement 8-bit PIO data transfers. Hale -- Hale Landis -- [EMAIL PROTECTED]
