This message is from the T13 list server.
On Sun, 14 Apr 2002 09:01:32 -0600, Pat LaVarre wrote: >This message is from the T13 list server. >> The host side using PIO >> has no way to suppress the >> transfer of the pad byte. >No. Hosts vary in quality of implementation. I was talking only of "standard" x86 systems... These systems have no way to suppress the transfer of the pad byte in PIO or DMA. >> On the x86 host side for PIO >> the software has no choice >> but to use the REP INSW >> or REP INSD instructions. >No. I do not understand your "No" response. Today's x86 PCI bus ATA host adapters do not support reading the ATA data register 8-bits at a time. Only word or dword accesses are supported. I have asked because I wanted to test an 8-bit ATA device (a CF in 8-bit mode) on a "standard" PC and it can't be done. But here I must say I do not want to flood the T13 list with a big discussion of how "double buffering" works or how some OS device driver stacks can only move data from memory to memory in 2, 4 or 8 byte chunks. This is not a T10 or T13 problem! >I hear that x86 REP INSD of Ata/pi data commonly doesn't work: >the bus trace the device sees doesn't match what appears in >memory. I have used my test software with REP INSD/OUTSD on lots of systems and devices and I have never seen a data compare error due to a x86 PCI bus host adapter failure. Yes, there are limitations on when/how REP INSD/OUTSD can be used but I will not go into that in this message. >Why not, how often not, who can fix it, who if anyone should fix >it ... those are our questions. I don't think so Pat... We haven't defined the problem yet. You apparently refused to look at by example of a Ultra DMA data transfer (because it didn't match the real world?). But I think it would show you how Ultra DMA works and therefore it would show you many of the issues you would need to address in any X-to-ATAPI bridge device, including the fact that there is no such thing a "residue" data, there is only a single pad byte in some cases. *** Hale Landis *** www.ata-atapi.com ***
