PCI arbiter doubts

Jun 14, 2005 1 Replies
P

Hi all,



I have some basic doubts on PCI arbiter.



1)how is the framen controlled -- i guess it is a shared resource on the PCI bus wher all the devices sitting on the PCI bus have access to it.
2)If a request is received from a device on PCI bus ,should the grant be issued immediately or should the PCI arbiter wait until the framen is dropped (asserted).
3)If a request is received from a device on PCI bus , but the framen is not dropped at all.how should the PCI arbiter react to this condition.

Regards, Praveen



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C

Hi Praveen,

1) FRAME, REQ, and GNT lines are *not* shared between different resources. There is a FRAME#(A), FRAME#(B), REQ#(A), REQ#(B), GNT#(A), GNT#(B), there is one of per bus master.

2) FRAMEN# is asserted (dropped) by the bus master after it receives a GNT#, it must be done as soon as possible for the bus cycle to begin. If the GNT# is desserted prior to the bus mater asserting FRAMEN# then it looses bus ownership and has to reabitrate. FRAMEN# is not asserted prior to GNT#.

3) see #2
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