AW: problem with PCI add-in cards with a PCI2PCI bridge on it

["Lange, Michael" <lange@dvs.de>]

Hi all.
We developed a PC card which include the Intel 21152 PCItoPCI bridge 
And we have a questions regarding the Bridge configuration - Does the
BIOS
initialize the configuration space of the PCI bridge ? In the event that
it
does, how can we guarantee that all the known BIOSs on the market will
be
able to perform the initialization. After the BIOS initialize the bridge
is
it necessary to configure additional registers in the bridge ?. 

Best regards.

Ilan Ossdon
R&D Gilat ltd.
Israel 

Ilan,

our experience is that (nearly) all BIOSs initialize the config
registers of the
bridge correctly with one exception : the cache line size register.

Some BIOS versions set this register to 8 and some set it to 2. This
could have an
effect on the performance. With our driver for our board (WIndows NT) we
can readjust the cache line size
register to 8.

Please also be careful with the selection of datalines (16 to 31 are
allowed) to be used
as IDSEL lines for the devices on the secondary PCI bus (behind the
bridge). You should NOT
use device number 0 (= data line 16) as IDSEL. There are some platforms
on which this device selection
will NOT work.

The best procedure for device selection is to use device numbers 4,8 and
12 ( = data line 20,24 and 28) only
in the case that only 1 IRQ line (INTA) should be shared by all devices
behind the bridge.

/Michael