L-Bus to U-Bus Interface (L2U)
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
11-9
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.
lists all reservation protocol cases supported by the L2U snooping logic.
11.7
L-Bus Show Cycle Support
The L2U module provides support for L-bus show cycles. L-bus show cycles are external visibility cycles
that reflect activity on the L-bus that would otherwise not be visible to the external bus. L-bus show cycles
are software controlled.
Table 11-2. Reservation Snoop Support
Reserved Location On
Intruding Alternate Master
Action Taken on stwcx cycle
L-bus
L-master
Request to cancel the reservation.
1
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.
U-master
Request to cancel the reservation.
U-bus
L-master
Block stwcx
2
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.
U-master
Block stwcx
External Bus
L-master
Block stwcx
U-master
Block stwcx
Ext-master
Transfer Status
3
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.
IMB3
L-master
Block stwcx
U-master
Block stwcx
IMB3-master
Transfer Status
Summary of Contents for MPC561
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Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
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Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...