Re2: uplcom(4) problem

Rahul Siddharthan rsidd at
Sat Oct 16 20:27:30 PDT 2004

Quoting Matthew Dillon <dillon at xxxxxxxxxxxxxxxxxxxx>:
> :    Hey Rahul, I got the PL2303 based usb->serial adapters but unfortunately
> :    they appear to work perfectly.  I connected up a modem via /dev/ucom0
> :    and dialed an ISP using ppp and it works.
>     I take it back!
>     It turns out that 'ppp' works fine, but 'pppd' cannot seem to read any
>     data back from the modem.  When I used pppd to talk to the modem via
>     ucom0 it failed to read() data from the modem even though the modem was
>     definitely sending data to the computer.  When I used pppd to talk to
>     the modem via cuaa0 it read() the data fine (and also hit the continuous
>     loop problem).
>     So I am able to reproduce *BOTH* issues.

Well, great that you see the problem!  Though in my case ppp didn't work either.

Also, when I tried backporting the linux 2.6 patch to linux 2.4, pppd
connects, but then doesn't seem to exchange any data after that.  It seems
a simple backport so I can't see what is wrong (but maybe that's why
they haven't backported it upstream, even in the latest prepatch...)

I think my modem is the "HX" kind, that's what the linux 2.6 change seems to


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