update on macserial/DMA

Takashi Oe toe at unlserve.unl.edu
Wed Oct 6 15:33:58 EST 1999


I re-wrote the serial DMA support code today and put the patch against
samba/vger linux-2.2.12 source trees (as of tonight) at
I think the patch includes most of macserial patches (Ben's and Lou's
are in there, for sure) that I know of.

This code is much better than the previous one in which it was fairly easy
to cause frame/overrun errors, although it was far better than the vanila
macserial (w/o DMA support).  To get a feeling of the driver's
performance, I tried the following operations while downloading 10 MB+
files at 49 kbps receiving/33.6 kbps transmitting modem<->ISP and 115 kbps
PMac<->modem (ftp on ppp link):

A: "dd if=/dev/zero of=400MB count=409600 bs=1024; cp 400MB /tmp; rm
B: planb+xawtv in grabdisplay mode (~10 fps, 640x480x4 bytes/frame)

With vanila macserial:
"A": ~200 overrun errors; ftp transfers were all aborted.

With previous DMA code:
"A": ~20 frame errors per ~600 packets
"B": a few frame errors per ~50 packets
"A+B": ~30 frame errors and a few overrun errors per ~600 packets

With this new DMA code:
"A" or "B" or "A+B": no error has been observed after about an hour of
trials (I did see a few frame errors when pppd started up once.)

These trials are pretty subjective, but I'm at least glad that it passed
all the tests I tried.

Takashi Oe

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