Intel 80312 I/O Companion Chip - ECEE

.Intel ® 80312 I/O Companion ChipPCI-to-PCI Bridge Unit4.9 Exclusive AccessThe bridge supports the PCI exclusive access mechanism using the P_LOCK# signal fordownstream accesses only. The bridge ignores the S_LOCK# signal for upstream accesses.Note:PCI Masters on the Secondary bus should not attempt to perform upstream locked transactions.Doing so may cause the PCI system to enter a state which prevents the Secondary locking masterfrom completing the locked request enqueued in the bridge, resulting in a system livelock.The bridge establishes itself as a locked target during a Delayed Read Request on the Primary PCIbus when P_LOCK# is deasserted in the address phase. When the bridge detects a downstreamlocked read request, a bridge lock sequence is started. This sequence is a series of state transitionswhich, when completed, will leave the bridge “locked” from all masters except for the masterwhich owns the P_LOCK# resource.Table 4-19.These states, and their transition criteria, are described in detail in Table 4-19.LOCK# Operation State DefinitionsState Primary Interface Secondary Interface TransitionOperation Definition Operation Definition TransitionUnlockedUnrestrictedAccept alltransactionson interface‘UnrestrictedAccept alltransactionson interfaceMove to Secondary Lockingwhen locked DRR received onPrimary interfaceSecondaryLockingRestrictedAll newdownstreamtransactionsretried.UnrestrictedAccept alltransactionson interfaceMove to Primary Locking whenbridge has finished mastering thelocked request on the Secondaryinterface. When an abort occurswhile mastering this transactionthe bridge will transition todirectly to the Unlocking state.PrimaryLockingRestrictedAll newdownstreamtransactionsretried.RestrictedAll newupstreamtransactionsretriedUpon completion of the lockedrequest the bridge transitions toLocked state. When the DRCsdiscard timer expires before thetransaction is completed, thebridge will transition directly tothe Unlocking state.LockedRestrictedOnly acceptsdownstreamtransactionsfrom lockmasterRestrictedAll upstreamtransactionsretriedMoves to Unlocking when Lockmaster on Primary interfacereleases P_LOCK# signal.When an abort occurs whilemastering a locked transaction,the bridge will release theS_LOCK# signal and transitionto the Unlocking state.UnlockingRestrictedAll newdownstreamtransactionsretriedRestrictedAll upstreamtransactionsretriedMoves to the Unlocked state assoon as the bridge hascompletely emptied all of itstransaction queues. Note: Incertain error situations this mayrequire that the discard timers beused to remove transactionswhich cannot otherwise becompleted.Developer’s Manual 4-61