This message is from the T13 list server.
On Wed, 10 Apr 2002 16:44:00 -0600, Pat LaVarre wrote: >This message is from the T13 list server. >I remember hearing some talk of teaching a host to read x1F2 & x03 I/O C/D >during a Dma data transfer to discover which way (In to the host or Out from >the host) the device was trying to copy the data ... This makes no sense because a device executing a DMA data transfer command should have status of BSY=1 until the command is completed. There is no "interrupt reason" data to be read by the host until the end of the command. Pat, where do you see such ideas documented anyway? >I've been told that by spec and in practice, UDma by default hangs if the >device & the host disagree over direction, which to my eye is an ok response >to such a provocation, though not best of class. (Best of class is to >discover the trouble and report it promptly, rather than waiting for a timeout >and reset.) PIO and MW DMA can hang too if the host and device don't understand the current command and the direction of data movement. I don't want to start that whole discussion of how both sides of the interface know what they are doing but again: The command codes defines the direction of data movement, nothing else does that, IO and CD do not do that. *** Hale Landis *** www.ata-atapi.com ***
