SB4002A_Data Sheet_EN

SB4002A
37
2.6 Exclusive Access
PCI bus provides the method that the master can exclusively access a specific target. This method
is called an exclusive access. It is started by LOCK#, one of the PCI signals.
The first transaction to start an excusive access for a specific target must be the memory READ
transaction. If this transaction is started, LOCK# must be deasserted at the first CLK of the address
phase, and LOCK# must be deasserted at the next CLK. An exclusive access is started when the
following data phase is completed. Once an exclusive access is started, the master must maintain
LOCK# in the assert state.
Once an exclusive access is started, in order that the master that has requested exclusive access
can re-access the target, the master must deassert LOCK# at the first CLK of the address phase,
and then, assert LOCK# at the next CLK. In order that the exclusive access is maintained after the
completion of the last data phase, LOCK# must be in the assert state. In order that the exclusive
access is released, LOCK# must be deasserted.
In order that the target should reject an exclusive access because it does not support exclusive
access or due to any internal reason, the target must terminate the first transaction with retry.
No other master than the one for the exclusive access can access the target because it cannot
deassert LOCK# at the address phase. If any other master attempts access, the target terminates
the transaction with retry.
Once an exclusive access is started, it is maintained even if retry of transaction or disconnect
occurs between the master and the target. If a target abort or master abort occurs, the exclusive
access is released.
DEVSEL#
1
TRDY#
5
AD
2
ADDRESS
CLK
LOCK#
4
IRDY#
FRAME#
DATA
3
Figure 2-9. Starting an Exclusive Access