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On a PC, the host controller should/would not move garbage to main memory, because the host controller will not transfer more data than what was specified in the transfer count in the DMA engine. So, the extra data, garbage, if it may be, is used to calculate the CRC, but the host controller would be very careful about stopping at exactly the point when the transfer count expires, as far as sending the received data to memory is concerned. Then, when software ends the DMA transfer by first clearing the START bit, the garbage data, if any, is flushed. TE. -----Original Message----- From: Pat LaVarre [mailto:[EMAIL PROTECTED]] Sent: Sunday, December 02, 2001 6:49 AM To: [EMAIL PROTECTED] Subject: [t13] UDma count well not - 3 of 4 - real examples <...> If UDma permits the sender to clock garbage, then even a host that double-buffers its i/o can't know how many bytes to move to/from app space. The garbage reaches all the way back to the app, just like the out-of-band communication that decides which bits of the command mean a count of bytes moving which way in what units. Subscribe/Unsubscribe instructions can be found at www.t13.org.
