darrylo@hpsrli.HP.COM (Darryl Okahata) (02/08/88)
In comp.sys.ibm.pc, paula@bcsaic.UUCP (Paul Allen) writes: > Jay Bowden posted a description of the brain-dead DMA hardware in the > IBM PC and look-alikes and asked what DOS does if you ask for a DMA > transfer that would cross a 64K boundary. [If you missed Jay's posting, > the PC DMA hardware is incapable of crossing a 64K page boundary during > a transfer. It simply wraps around to the begining of the page!] > > Basically, you only need to worry about this if you are programming the > DMA chip directly. You just allocate a one-block buffer in your driver You also have to worry about this if you use the ROM BIOS to read from a disk; if the buffer that you are using to read/write data crosses a 64K boundary, the transfer will fail (I believe the error code returned is "DMA_BOUNDARY" -- 09H). > ------------------------------------------------------------------------ > Paul L. Allen | paula@boeing.com > Boeing Advanced Technology Center | ...!uw-beaver!ssc-vax!bcsaic!paula -- Darryl Okahata {hplabs!hpccc!, hpfcla!} hpsrla!darrylo CompuServe: 75206,3074 Disclaimer: the above is the author's personal opinion and is not the opinion or policy of his employer or of the little green men that have been following him all day.