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Jim's right that you can always get (i.e. DATA IN) fewer bytes than the host specified in the ALLOCATION LENGTH or PARAMETER LIST LENGTH parts of the CDB on a successful command. This is not however true for DATA OUT commands. The difference is that the device always has to terminate the command on a success, and relies on the TRANSFER LENGTH value passed to it and counting the number of bytes transferred in order to figure that out. If the host just stopped sending more data, the device just treats that as a pause in the command, for which there is no timeout or other provision that allows successful command termination. Practical impact is that I don't think you can get fewer bytes on a successful WRITE BUFFER command (or MODE SELECT, or LOG SELECT, etc...). Jim -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Tuesday, February 26, 2002 10:06 AM To: [EMAIL PROTECTED] Cc: [EMAIL PROTECTED] Subject: Re: [t13] ATAPI DMA Byte Count usage for Data commands This message is from the T13 list server. For tape,the common commands would be: For DATA commands: the amount of data you actually get from the drive may be FEWER than requested if you encounter an error: medium error, filemark, EOD, physical end of medium, etc. <ALWAYS> look at the 'residual count' in the REQUEST SENSE response. READ(6), WRITE(6) For ANY non-DATA commands: You can always get FEWER bytes than requested from these commands if the device does not have the 'allocated' bytes available or valid for the particular command: This is normal, and is NOT an error. INQUIRY, REQUEST SENSE, MODE SENSE, LOG SENSE READ POSITION, READ BUFFER, WRITE BUFFER, etc. - Jim Hatfield Sr. Firmware Engineer Overland Data Inc. ===================================================== Subject: [t13] ATAPI DMA Byte Count usage for Data commands Question: Are there any ATAPI Data commands (PLEASE note DATA (Read 10 etc)), where the data length is not the same as the requested length ? For non-data commands, I know of Request Sense Mode Sense Are there other common ones for CD/RW/DVD and Tape ? Jeff Jeff Wolford Email: [EMAIL PROTECTED] Senior Storage Architect Storage Interface and Tools - PC Storage Group Voice: (281) 514-9465, Pager: (800) 973-5739 Compaq Computer Corporation ******************************************************************** Get it all in Overland's revolutionary new Neo tape library. Non-stop operation. Expansion on demand. Easy to use For more information on Neo: http://www.overlanddata.com/mktg.nsf/lookup/lxn4000.pdf/$file/lxn4000.pdf For more information on Overland: http://www.overlanddata.com ******************************************************************** Subscribe/Unsubscribe instructions can be found at www.t13.org. Subscribe/Unsubscribe instructions can be found at www.t13.org.
