Re: Arbitrator

["Richard Iachetta" <iachetta@us.ibm.com>]

Delaying REQ should be ok but I don't think its safe to delay GNT by a
clock.  The motherboard arbiter is allowed to deassert GNT at any time so
if you delay GNT by a clock you could get into a situation where your card
sees GNT asserted but the motherboard is no longer granting it which could
cause the card to start a transaction when it doesn't own the bus.

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



                                                                                                                                              
                      Jon Keeble                                                                                                              
                      <j.keeble@fairlight        To:       pci-sig@rollsroyce.znyx.com                                                        
                      esp.com.au>                cc:                                                                                          
                                                 Subject:  Arbitrator                                                                         
                      04/15/02 11:18 PM                                                                                                       
                                                                                                                                              
                                                                                                                                              



I have a prototype 'riser' card that has a couple of PCI slots that plugs
into a PCI bus, and a PLD for handling arbitration.

The 'secondary arbitrator' is to support BR / BG for cards plugged into the
riser.

For my purposes the priority of each card can be ignored i.e. simultaneous
requests could always be given to one particular slot.

Having stared at the PCI arbitrator documentation for a while, I've
concluded that it is
  - 'safe' to delay a GNT (from the mother board) by one cycle to either
card under all possible conditions.
  - 'safe' to delay a REQ (from either card) to the motherboard.

If anyone is aware of anything to the contrary pls let me know.

Regards

Jon Keeble.