Re: FFs for GNT and REQ

[iachetta@us.ibm.com]

>When your REQ# is asserted and once Bus Arbitor gives you GNT#, it will
not
>disappear for at least 5 clocks or FRAME# is asserted, whichever comes
>first.
>
>My reason is not from PCI specs, but from my reasoning: 5 clocks are
needed
>to guarantee that some PCI masters behind bridge get the correct GNT#
>response from arbitor. That FRAME# is asserted means PCI Bus client has
got
>the bus access. My guess is as much as 16 clocks may be generated by PCI
>bridge to wait for FRAME# assertion before arbitor deassert GNT#.

Weng, I don't agree with this.  The PCI spec. says that "The arbiter may
deassert an agent's GNT# on any clock".  I don't follow what you are saying
about the 5 clocks.  A master on the secondary side of the bridge does not
have to be granted both the secondary and primary sides.  The arbitration
on both sides is decoupled, especially with posted writes and delayed
reads.

Rich Iachetta
IBM Microelectronics Division -- Austin
World Wide Field Design Center
Phone: 512-838-6305   Tie Line: 678-6305