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

[Giuseppe Ciaccio]

On Thu, 6 Jul 2000, Andrew Morton wrote:

> > Driver responsibility ?!?  I was pretty sure 802.3x STOP-GO packets
> > were hardware-managed.  I'm sure it is so with the Alteon AceNIC
> > Gigabit Eth card, and thought it was the same with all other 802.3x-capable
> > devices.
> 
> That's my understanding.  The 3c905C will recognise and act upon
> incoming PAUSE frames if programmed to do so.

OK but it will do this in hardware; the driver is not involved at all.
The only driver's responsibility is to enable/disable the feature.

> But it won't generate
> outgoing ones in hardware (pretty sure of this).

You are right.

So, flow ctl never runs when using a crossover cable (because none of the
connected devices can generate PAUSE packets), and everything is fine.

Instead, flow ctl can actually run if a 802.3x switch is used (since it can
generate PAUSE packets), provided that the NICs advertise the feature
(otherwise the switch would not enable flow ctl).  Troubles can arise
if the NIC advertises flow ctl but does not act properly upon receiving
PAUSE pkts.

You said the patch you sent me before is for enabling the NIC flow ctl.
Does it mean the 3c905C advertises flow ctl even if not enabled (like my
switch does indeed)?

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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