Hi, adding to Bart's / Arkady's answers... > Do FreeDOS disk accesses via INT 21h, INT 13h, INT whatever, read and write > directly from/to a passed address or do they always buffer the disk > access? Never? Sometimes?
While this ought to take place at int 13 level (to give programs like disk tools some bonus help), FreeDOS has extra buffer logic at higher level: Transfers are split in two if they cross a DMA boundary, and the sector at the 64k boundary is accessed with help of a deblocking buffer in low RAM. If a buffer is in UMB, HMA, or ROM, the access is implemented by transferring one sector after another through the single sector deblocking buffer. As far as I remember, this buffer is also used for "rounding" accesses to whole sector multiples. In addition, BUFFERS usage can avoid the actual disk access altogether, depending on buffer cache contents. Check dsk.c LBA_Transfer, as Arkady said... Note about LBAcache: It has no local buffers, but copies between XMS and the buffer provided by the user / kernel for int 13. However, TICKLE has local buffers - but by default, it affects only floppy access. So you should load TICKLE low, if there are DMA problems in UMBs. There is no VDS support, but it would be interesting to know how to do it - IF it would work for floppy DMA as well. I think it would be nice to have configurable "a000" value in kernel, to reduce buffering if UMBs are DMA-able and to double-buffer everything in another (no idea why) case. Default is, however, to double-buffer all access in UMB / HMA. But as LBA_Transfer does this, direct int 13 access is not protected from having buffers in UMB (int 13 itself has no automatic "double-buffering"). One could move the code around, but it is better to clone it (protect both int 13 and all block devices, even non-int-13 ones) and add int 13 hooking to the kernel (and int 2f.13). Eric. ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/ _______________________________________________ Freedos-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/freedos-devel
