🚀 go-pugleaf

In article <1992Jul22.015106.230532@cs.cmu.edu>, ralf+@cs.cmu.edu (Ralf Brown) writes:
>In article <tfiske.711742881@qualcom> tfiske@qualcom.qualcomm.com (T.J. Fiske) writes:
>}The 8237A DMA chip on the PC:
>}on the AT and higher models, there are 8 dma channels.
>}I need to program channel 5, since I need to do 16 bit
>}dma transfers.  Anyways, to progam the target address
>}correctly, it needs a "page" address at port 0x8b.
>}What is this page address, and how can I do an address
>
>The high eight bits of the 24-bit linear address, which you compute as
>	((long)segment)<<4 + offset
>
>(of course, this computation applies only in real mode)

For 16 bit channels, the page registers contain bits 17 - 23 (the upper *7*
bits of the 24-bit linear address). The 8237 address registers are programmed
with address bits 1-16, while bit 0 is forced to 0 since 16-bit DMA
transfers are always to even addresses. This scheme also has the implication
that the page size is 128 kbytes, as opposed to 64 kbytes for 8-bit transfers.

-- 
***** hlj@hal.nta.no (Harald Ljo"en) expressing his private opinions ******