Dear All, Sorry, Eric again! Hoping that nobody MISLEAD by him, Jack have a message to clear up:
===== Re: the 16-Jul-2005 comments by Eric Auer on FD-Devel (in reply to the man that wants larger disk partitions), be advised that UDMA2 does not process ONLY the following I-O requests: A) Requests issued while the driver is "busy" with ANOTHER request. The second request is REJECTED with BIOS error code 1 (invalid function). This should never happen, unless some "hot shot" issues an I-O request from within an interrupt routine! DOS drivers are NOT designed to be "re-entrant"! NOTE that the driver DOES wait for overlapped output to finish and will not reject a second I-O request if actual overlapped output is running. B) Requests whose sector count is zero or over 128. Such requests are always passed to the BIOS; it can "complete" a zero-sector request without having logic in UDMA2 to do this. Also, a sector count of 255 (FFh) may denote a "64-bit" I-O request. Neither UDMA2 nor most DOS variants handle these! C) Requests whose buffer address is FFFFFFFFh, denoting a "64-bit" I-O request. Such requests are always passed to the BIOS, same as in (B) above). ALL other I-O requests WILL be handled by UDMA2, UNLESS the driver IS NOT using its XMS memory buffer. If the system was loaded without an XMS manager (HIMEM, FDXMS, etc.), or if UDMA2 was loaded with its /B switch, ONLY THEN will UDMA2 pass misaligned or boundary-crossing I-O requests to the BIOS. For the 99% of us who DO have XMS memory available and who do NOT use UDMA2 with /B, the driver will process ALL legitimate I-O requests by itself, either by using direct UltraDMA, or by using UltraDMA to or from its XMS buffer, which is nearly as fast. As "friend" Eric has again MISREPRESENTED what UDMA2 does, you may want to post the above comments on FD-Devel as a "reply" to him! Note also that items (A) thru (C) above apply to XDMA as well. However, as XDMA requires an XMS buffer, it has the ability to execute any legitimate disk I-O request and will NEVER "pass" legitimate I-O to the BIOS! UDMA2 really SHOULD be written this way; but I WILL NOT deal further with those in FreeDOS who insist on "DMA only" mode! Best wishes! Jack R. Ellis ===== ------------------------------------------------------- SF.Net email is sponsored by: Discover Easy Linux Migration Strategies from IBM. Find simple to follow Roadmaps, straightforward articles, informative Webcasts and more! Get everything you need to get up to speed, fast. http://ads.osdn.com/?ad_id=7477&alloc_id=16492&op=click _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
