pi7c8150b Pericom Semiconductor Corporation, pi7c8150b Datasheet - Page 61

• Manufacturer Part Number: pi7c8150b
• Description: Asynchronous 2-port Pci Bridge
• Manufacturer: Pericom Semiconductor Corporation

06-0044
When the target resides on another PCI bus, the master must acquire not only the lock on
its own PCI bus but also the lock on every bus between its bus and the target’s bus. When
PI7C8150B detects on the primary bus, an initial locked transaction intended for a target on
the secondary bus, PI7C8150B samples the address, transaction type, byte enable bits, and
parity, as described in Section 3.5.4. It also samples the lock signal. If there is a lock
established between 2 ports or the target bus is already locked by another master, then the
current lock cycle is retried without forward. Because a target retry is signaled to the
initiator, the initiator must relinquish the lock on the primary bus, and therefore the lock is
not yet established.
The first locked transaction must be a memory read transaction. Subsequent locked
transactions can be memory read or memory write transactions. Posted memory write
transactions that are a part of the locked transaction sequence are still posted. Memory read
transactions that are a part of the locked transaction sequence are not pre-fetched.
When the locked delayed memory read request is queued, PI7C8150B does not queue any
more transactions until the locked sequence is finished. PI7C8150B signals a target retry to
all transactions initiated subsequent to the locked read transaction that are intended for
targets on the other side of PI7C8150B. PI7C8150B allows any transactions queued before
the locked transaction to complete before initiating the locked transaction.
When the locked delayed memory read request transaction moves to the head of the
delayed transaction queue, PI7C8150B initiates the transaction as a locked read transaction
by de-asserting LOCK_L on the target bus during the first address phase, and by asserting
LOCK_L one cycle later. If LOCK_L is already asserted (used by another initiator),
PI7C8150B waits to request access to the secondary bus until LOCK_L is de-asserted
when the target bus is idle. Note that the existing lock on the target bus could not have
crossed PI7C8150B. Otherwise, the pending queued locked transaction would not have
been queued. When PI7C8150B is able to complete a data transfer with the locked read
transaction, the lock is established on the secondary bus.
When the initiator repeats the locked read transaction on the primary bus with the same
address, transaction type, and byte enable bits, PI7C8150B transfers the read data back to
the initiator, and the lock is then also established on the primary bus.
For PI7C8150B to recognize and respond to the initiator, the initiator’s subsequent
attempts of the read transaction must use the locked transaction sequence (de-assert
LOCK_L during address phase, and assert LOCK_L one cycle later). If the LOCK_L
sequence is not used in subsequent attempts, a master timeout condition may result. When
a master timeout condition occurs, SERR_L is conditionally asserted (see Section 6.4), the
read data and queued read transaction are discarded, and the LOCK_L signal is de-asserted
on the target bus.
Once the intended target has been locked, any subsequent locked transactions initiated on
the initiator bus that are forwarded by PI7C8150B are driven as locked transactions on the
target bus.
The first transaction to establish LOCK_L must be Memory Read. If the first transaction is
not Memory read, the following transactions behave accordingly:
Type 0 Configuration Read/Write induces master abort
Type 1 Configuration Read/Write induces master abort
I/O Read induces master abort
I/O Write induces master abort
Page 61 of 108
ASYNCHRONOUS 2-PORT PCI-TO-PCI BRIDGE
APRIL 2006 – Revision 2.02
PI7C8150B