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There is no contradiction. Note that in the case of READing if the device "ignores" an improper PIO, then what physically happens is that the host will latch the data bus with whatever happens to be out there (since the device made no special attempt to put anything on the bus, and there is no interlock between the host and device on a single PIO read). Whatever happens to be out there is, of course, indeterminate unless you have specific prior knowledge of what was happening on the bus. On writes the host information is ignored by the device, which in turn results in an indeterminate behaviour (once again, specific to context). Bottom line is that in PIO if the host wants to do something, then physically something WILL happen. But the results can be indeterminate if the device does properly understand what is going on or ignores what is going on. Jim -----Original Message----- From: Pat LaVarre [mailto:[EMAIL PROTECTED]] Sent: Thursday, December 06, 2001 4:43 PM To: [EMAIL PROTECTED] Subject: Re: [t13] Re: unexpected data clocks This message is from the T13 list server. Anyone out there able to resolve easily the apparent paradox between these short extracts from Jim's & Hale's remarks? >>> "Mcgrath, Jim" <[EMAIL PROTECTED]> 12/06/01 12:14PM >>> ... In ATA-6 r 3, section 7.6.4 (Effect of the Data Register), it states that: ... The results of a read during a PIO in or a write during a PIO out are indeterminate." So the case is covered, although documented incorrectly (note: the sense of DATA-IN and DATA-OUT are reversed in the above text, so that should be corrected). ... >>> [EMAIL PROTECTED] 12/06/01 12:45PM >>> On Thu, 06 Dec 2001 10:54:58 -0700, Pat LaVarre wrote: >For Pio I guess I think of this as a special case of >how to respond to Pio r/w of the x1F0 Data register >at times when DRQ is clear. An read or write of the Data register while BSY=1 or while BSY=0 DRQ=0 is ignored. See the I/O response tables. It has been this way since before ATA-1. ... Maybe the same thing should apply to an unexpected read/write of the Data register during a PIO data transfer command? ... Subscribe/Unsubscribe instructions can be found at www.t13.org. Subscribe/Unsubscribe instructions can be found at www.t13.org.
