On Sat, Jul 20, 2002 at 06:58:41AM +0000, Matthias Scheler wrote:
> In article <20020718183334.A3160@antioche.lip6.fr>,
> 	Manuel Bouyer <bouyer@antioche.lip6.fr> writes:
> > ... and I start wondering if a quad-port PCI ethernet can really
> > work if it includes a PCI/PCI bridge
> 
> I used an Adaptec 3940UW for years which has two UW SCSI chips behind
> a PCI bridge. Although it could transfer twice as much data as your
> quad-port PCI ethernet card through the PCI bridge (a DEC one IIRC)
> I never had any problems.

The timing constraints are not the same: with SCSI there is flow
control, the scsi device will stop sending data if the host adapter
can't write data fast enouth to RAM. With network adapters, the busmaster
device has to write data to RAM as fast as they come in, or you loose packets.
In my case it seems that the PCI bridge "lowers" the priority of devices
behind it, and making the ethernet chips loose packets if there
are other activity on the PCI bus.
The problem with the DFE580 is that the receive fifo is only 2k, which makes
things worse. the 570 had dec 21143 chips with 8k fifo, and was much more
usable (although receive overflow can happen from time to time).

> 
> And the Compaq Dual Port Netelligent 10/100 TX - you have those, too -
> in my server never caused trouble, too, although it has two TI chips
> behind an Intel PCI bridge.

No, the Dual Port Netelligent I have don't have a PCI bridge on it, just
2 thunderlan devices (I guess one PCI slot can accept 2 PCI devices).
But there have been different versions of the Netelligent, I think the last
one have intel ethernet chip instead of the ThunderLan

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
--