[eepro100] Intel HPQ and MAC Setting question
Mon Nov 26 14:44:01 2001
On Mon, 26 Nov 2001, Markus Fraedrich wrote:
> Due to a project im studying for the Timing of Fast Ethernet NICs to
> generate a QoS.
> Unfortunately I didnīt get the User Manual for the 82557.
That's usual -- Intel rarely provides complete programming information.
I haven't gotten an update from Intel for years.
> Does anyone know if its possible to change/increase the IFS setting of the
> NIC, and knows the Register Adress.
Yes, it's at offset 2 in the configuration block. The extended IFS is
tied to the PCI bus speed, with the IFS never being less than the
standard Ethernet IFS. If you are running a 33Mhz PCI bus, a setting of
'4' correesponds to the 960ns minimum IFS. A setting of '5' results in
an IFS of 5*8*30ns = 1200ns.
Changing the IFS on the 8255* chips requires sending a configure
command. This overhead makes it impractical to change the IFS
Note that changing the IFS is not a good solution to QoS. You will
change the fairness of the contention-based network, but the change is
very difficult to predict. If you have a switch-based network and want
to experiment with QoS you should really be looking at real-time packet
scheduling and rate limiting.
Donald Becker firstname.lastname@example.org
Scyld Computing Corporation http://www.scyld.com
410 Severn Ave. Suite 210 Second Generation Beowulf Clusters
Annapolis MD 21403 410-990-9993