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Mark, I assume you mean Ultra DMA (or UDMA) for DMA. You may want to look over the archives for the past month or so - this topic was recently extensively discussed. One short response - the UDMA protocol has nothing to so with sector size. The two are completely independent. During a command the device with transfer an amount of data equal to the total amount requested at the command level, in one or more UDMA bursts of potentially random sizes. The size of the burst is determined by the availability of the data (i.e. when there is no more buffered data to transfer the device may terminate the burst and start a new one when data becomes available again). For writes you (the host) clock out the data, while for reads the device clocks out the data. This is unlike PIO (or Multiword DMA), where the host always clocks out the data. That's why you need a transfer count per interrupt in PIO (since you need to know ahead of time the amount of data available so you can supply the correct number of clocks to do a PIO read). You don't need that for UDMA - with the device providing the clocks for reads, your role is that of the slave (the device terminates the UDMA burst when it runs out of stuff to send). So in short pick whatever sector size you want. It does not make any difference to the DMA transfer mechanism. Of course, you need to know the sector size at higher levels of software, but at those levels there are of course ways of determining that (i.e. what format is the media, ISO or Redbook?). Jim -----Original Message----- From: Mark Sawyer [mailto:[EMAIL PROTECTED]] Sent: Thursday, January 24, 2002 2:14 PM To: [EMAIL PROTECTED] Subject: [t13] Question: ATAPI (CDROM) sector size for DMA This message is from the T13 list server. I have a question that I am hoping someone on this list can help me find an answer to ... I apologize in advance if this question is inappropriate for this forum ... I am involved with the development of a hardware driver which interfaces to several ATA/ATAPI devices (i.e. HDD's, CDROM's, compact flash, etc...) My problem is determining the correct sector size for CDROM's when performing DMA. In the case of PIO, this is not a problem since the device tells me how many bytes to expect. The platform (it's custom) I am working on requires support for both data CD's (ISO9660 - 2048 byte sectors) and audio CD's (Redbook - 2352 byte sectors) ... I realize that this is an issue of the media present in the device but what is the preferred method of determining sector size? Thanks for any help you can give me, /mbs --- Mark Sawyer Sawyer Software Solutions, LLC 2 Lincoln Drive, Bow, NH 03304-3209 Tel: 603-228-9214 / Cell: 603-496-3509 / FAX: 603-228-4810 --- AOL's AIM: FirmwareWizard _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com Subscribe/Unsubscribe instructions can be found at www.t13.org. Subscribe/Unsubscribe instructions can be found at www.t13.org.
