Arbitration question (GNT#->FRAME# latency)

[Tom Hicks <thicks@fore.com>]

I have a question for PCI designers out there:

The last paragraph of section 3.4.1 (Arbitration) says:

    "A master that has requested use of the bus that does not assert
    FRAME# when the bus is in the Idle state and its GNT# is asserted
    faces the possibility of losing its turn on the bus."   

Does anyone know of an arbiter/PCI chipset that doesn't always assert
GNT# for at least two clock cycles?  We have not yet encountered a
chipset that does not provide at least two clocks for GNT#.

I am interested in this because I would like to use the first cycle
when GNT# and Idle are detected to turn on output enables, and the
second cycle when GNT# and Idle are detected to assert FRAME# and
address.

I have found that many PCI buffers are designed such that the Z-to-low
and Z-to-high path is not considered the critical path, since the output
enable could be driven a clock earlier.  But for the GNT#/FRAME# case,
this assumption is bad.  If I could rely on GNT# being asserted for at
least two clocks, I could turn on the output enable in one clock and
then assert FRAME#/AD in the next clock and still meet the Tval requirements.

Thanks in advance for any insight/help,
Tom

--
Tom Hicks			Fore Systems
Design Engineer			174 Thorn Hill Rd
Adapter Group			Warrendale, PA 15086
thicks@fore.com	
.