[vortex] 3c905C: Packet losses (a more precise description)

[Giuseppe Ciaccio]

On Wed, 5 Jul 2000, Bogdan Costescu wrote:

> > Basic registers of MII PHY #0:  0000 0000 0000 0000 0000 0000 0000 0000.
> >  Basic mode control register 0x0000: Auto-negotiation disabled, with
> >  Speed fixed at 10 mbps, half-duplex.
> >  Basic mode status register 0x0000 ... 0000.
> >    Link status: not established.
> >  Link partner information information is not exchanged
> > when in fixed speed mode.
> 
> Now this is strange. Why mii-diag cannot find the right registers when
> autonegotiation is disabled ? Donald, do you have any theory ?
> 
> > Autoneg does not occur (it is switched off at the NICs).
> > mii-diag reports "10 mbps"; however, the LEDs in the back are saying
> > "100 mbps".  Who is right?
> 
> For some reason, mii-diag cannot read correctly the MII registers; the
> interpretation (10 mbps, link not established and so on) is correct.
> 
> > Crossover cable, and repeater hub:  mii-diag as above, no packet losses.
> 
> Which one above: with all registers read as 0 (non-autoneg. case) or with
> useful data (autoneg. case)?

The one with all registers read as 0.

When I disable the autoneg, I set both NICs to 100base-TX half-duplex.

> > Apparently, it is the switch' fault.  However, if I use other NICs, like the
> > DEC DE500, the Intel EEPro 100 (one with 82557 and the other with 82558B),
> > or even the old 3COM 3c905, in place of the 3c905C, no packet losses are
> > observed through the very same switch.
> > 
> > A problem with flow ctl between my switch and the 3c905C adapters?
> 
> Might be! But are the other NICs supporting/using/reporting flow control ?

The old 3c905 has no flow ctl, like the DEC DE500 and the Intel i82557;
the Intel i82558B probably has flow ctl, but will not use it, as my
other Intel adapter (i82557) cannot advertise the feature.

> If they don't support and use it, the switch will not use it and you're on
> the safe side (if flow control is the real cause). As 3C905C always
> advertise flow control, if the switch also advertise it (not _really_
> disabled) then it will be used.

This means that the 3c905C adapters will however use flow ctl when connected
by a crossover cable.  Since there is no packet loss in this case,
the faulty device must be the switch.

Could you kindly perform a "ping -f" with your own 3c905C cards and switch
and report me the outcome after a few (20 - 30) seconds of run (possibly
with unloaded switch)?  Could you also send me the output of mii-diag
with your cards?

Giuseppe


Giuseppe Ciaccio               http://www.disi.unige.it/person/CiaccioG/
DISI - Universita' di Genova   via Dodecaneso 35   16146 Genova,   Italy
phone +39 10 353 6638          fax +39 010 3536699 ciaccio@disi.unige.it
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