On Thu, Jun 14, 2001 at 01:31:27PM -0400, Pete Zaitcev wrote:
> > > > > https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=39238
> > > > >
> > > > > I think I'll just take that flag off from the read URB for us.
> > > >
> > > > ...and you get 5x slowdown on PCI bandwidth when using modem...
> > >
> > > Users prefer 5x slowdown to not working modem, evidently.
> >
> > Uh? The modem should work just fine with the NO_FSBR flag, just with its
> > speed limited to about 64 kbytes/second. (One 64-byte packet per USB
> > frame). And 64 kbytes/second is quite a lot for any modem out there,
> > even ISDN can't do more than 16 kbytes/second uncompressed.
> >[...]
> > There may be different problem, though. I do have the 3Com ISDN TA, so I
> > can test it. I don't have an ISDN line, though. I'll try to enable
> > internal loopback in the TA.
>
> "The modem should work", but it does not. See the bug.
>
> Personally I think the 3Com crap is busted in the flow
> control department, so when it spits "CONNECT", it gets
> overun by the data inside the 3Com box. It does not change
> much in the argument though.
I've had similar problems with 3Com OfficeConnect modem - died after
"CONNECT", because it didn't have the baud rate set. What would be a
baudrate good for on USB, no idea, but it needed to have it set.
Perhaps there is indeed something with flow control, and perhaps we
indeed need to be able to receive more than the 64 bytes in a frame, but
still if there is any method to do that other than enabling FSBR, we
need to try it.
There might be a vendor specific interface on the modem for example,
with an irq endpoint. Many modems do that, because this is the way to
workaround the FSBR problem. But the ACM spec doesn't allow it (though
it does have an irq endpoint, but it isn't used for rx buffer status).
> BTW, you miscalculated the ISDN speed: it's dual channel,
> not single, so it's 32 KB/s when sustained.
2B+D ISDN line has one control channel and two 64 kbit data channels,
that's 128 kbit/sec. With 8 bits per byte, we get 16 kbytes per second.
I think I didn't miscalculate anything.
--
Vojtech Pavlik
SuSE Labs
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