🚀 go-pugleaf

In article <197@oliveb.UUCP> spud@oliven.UUCP (John Purser) writes:
>In article <1189@dataio.UUCP> bright@dataio.UUCP (Walter Bright) writes:
>>I am interested in copying pixel data from one page to another on the
>>IBM EGA. This involves moving 128k bytes of data. Doing it with a
>>REP MOVSW takes about 1/2 second (on an AT), which is too slow.
>>Does anyone know
>>how the DMA channel could be programmed to do this? It is not clear
>>from the documentation how to program the DMA chip, or even if
>>it is capable of memory-to-memory transfers.
>
>How did you arrive at the time of 1/2 second? The way I figure this
>it should only take about .05 seconds. According to the 286 programmers
>referance guide a REP MOVSW takes 5+(4*CX) clocks. In your example that would
>be 64k words times 4 plus 5 or a total of 262,149 clocks. The clock speed
>of the AT is 6Mhz so dividing the 262,149 by 6,000,000 leaves us with .045
>seconds.

I did some checking. First off, the EGA is 8 bit ram, so the 128kb move
should take .09 seconds. Second, the EGA needs 4 out of 5 memory cycles
to do refresh, so the copy winds up taking about 1/2 seconds. DMA obviously
wouldn't help much here.

Also, nobody replied with a method of doing memcpy()s with the DMA.