Motorola MPC533 Reference Manual page 426

Reservation Support
Storage reservation is set regardless of the termination status (address or data phase) of the
lwarx access. Storage reservation is cleared regardless of the data phase termination status
of the stwcx access if the address phase is terminated normally.
Storage reservation will be cleared regardless of the data phase termination status of the
write requests by another master to the reserved address if the address phase of the write
access is terminated normally on the destination (U-bus/L-bus) bus.
If the programmable memory map of the part is modified between a lwarx and a stwcx
instruction, the reservation is not guaranteed.
11.6.3 Reserved Location (Bus) and Possible Actions
Once the RPCU core reserves a memory location, the L2U module is responsible for
snooping the L-bus and U-bus for possible intrusion of the reserved location. Under certain
circumstances, the L2U depends on the USIU or the UIMB to provide status of reservation
on external bus and the IMB3 respectively.
Table 11-2 lists all reservation protocol cases supported by the L2U snooping logic.
Reserved Location On
L-bus
U-bus
External Bus
IMB3
1
If the RCPU tries to modify (stwcx) that location, the L2U does not have enough time to stop the write access
from completing. In this case, the L2U will drive cancel-reservation signal back to the core as soon as it
comes to know that the alternate master on the U-bus has touched the reserved location.
2
If the RCPU tries to modify (stwcx) that location, the L2U does not start the cycle on the U-bus and it
communicates to the core that the current write has been aborted by the slave with no side effects.
3
If the RCPU tries to modify (stwcx) that location, the L2U runs a write-cycle-with-reservation request on the
U-bus. The L2U samples the status of the reservation along with the U-bus cycle termination signals and it
communicates to the core if the current write has been aborted by the slave with no side effects.
11-10
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Table 11-2. Reservation Snoop Support
Intruding Alternate Master
L-master
U-master
L-master
U-master
L-master
U-master
Ext-master
L-master
U-master
IMB3-master
MPC533 Reference Manual
Action Taken on stwcx cycle
Request to cancel the reservation.
Request to cancel the reservation.
2
Block stwcx
Block stwcx
Block stwcx
Block stwcx
3
Transfer Status
Block stwcx
Block stwcx
Transfer Status
1
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