RE: Bridge versus Simple Device

[Horkel Milan <m.horkel@decros.cz>]

It is important to consider what is BRIDGE and what is PCI-TO-PCI BRIDGE

PCI-TO-PCI BRIDGE connects PCI bus with another PCI bus and gives the system
HOST ability to enumerate secondary PCI bus devices and the ability to
configure them. For this functionality PCI-TO-PCI BRIDGE have different set
of PCI configuration registers (TYPE 01).

Generic BRIDGE do not have this ability. It have standard set of PCI config
registers (TYPE 00). PCI system (HOST processor with lets say PCI BIOS) do
not know anything about what is behind that bridge. BRIDGE can be
MASTER/TARGET or TARGET-ONLY device. 

Milan Horkel
DECROS
HW Development

-----Puvodni zprava-----
Od: James Murray [mailto:jmurray@triscend.com]
Odeslano: 27. unora 2001 0:43
Komu: PCI SIG
Poedmit: Bridge versus Simple Device


I have an application (ASIC) where I have an embedded processor on a
"local" bus containing various other local bus masters and targets. I
want to design a PCI bus master/target interface that will reside on
this local bus.

Here is the dilemma:
I would really like to consider this ASIC as being a PCI "Simple
Device", as opposed to a "Bridge", purely because of the reduced
complexity of the Simple Device Ordering rules. On one hand, the spec
says that in general, if a processor is residing behind the PCI bus
interface, the device is considered to be a Bridge. If memory writes are
posted, the device is classed as a Bridge.

Question: If I use an internal DMA engine to move data into a Mater
Write FIFO, and generate an IRQ to the processor WHEN THE TRANSACTION
COMPLETES ON THE PCI BUS,  could I then call myself a "Simple Device" ??

Thanks in advance for any input.

James