[tulip] No Link Beat on Cable Modem

David davidvickers1@home.com
Wed, 28 Mar 2001 23:28:05 -0700


> This is the correct behavior.  The 21041 will not transmit unless it
> sees 10baseT link beat.

> This can be overridden by clearing CSR14 bit 12 (0x1000).

> Please try the following:
>   Change your media type to '3'  (options=3)
>   Change line 477 as follows:

> -static u16 t21041_csr14[] = { 0xFFFF, 0xF7FD, 0xF7FD, 0x7F3F, 0x7F3D, };
> +static u16 t21041_csr14[] = { 0xFFFF, 0xF7FD, 0xF7FD, 0x6F3F, 0x7F3D, };


Donald,

Thanks for the quick reply.  Unfortunately, it didn't seem to solve the
problem yet.  I now get:

tulip.c:v0.92t 1/15/2001  Written by Donald Becker <becker@scyld.com>
  http://www.scyld.com/network/tulip.html
eth0: Digital DC21041 Tulip rev 33 at 0xd001e000, 00:E0:29:61:67:16, IRQ
9.
eth0: Transceiver selection forced to 100baseTx.
eth0: 21041 Media table, default media 0800 (Autosense).
eth0:  21041 media #0, 10baseT.
eth0:  21041 media #4, 10baseT-FDX.

(but no more messages), but I still can't ping my router.  Since the
cable modem is clearly violating the spec, I'll try the following:

1.  Ask AT&T if they will swap out a different cable modem box (they're
giving new customers a different model).

2.  Try inserting an active hub between my PC & the cable modem.  Some
friends with a nearly identical situation (same cable modem, same
ethernet card, same Linux kernel) are running fine, the only difference
is that they have an active hub, which I assume might insert a link
beat.

If you have any more driver suggestions, I'll try those, too.  However,
I'm now certain that the fault lies with the cable modem, not just me
doing something wrong, so hacking the tulip driver to work with a broken
peer isn't a high priority (although the Win95 driver does seem to do it
somehow).

Thanks again for your time and everything you've done for the Linux
network drivers!

-Dave