L-Bus to U-Bus Interface (L2U)
MPC561/MPC563 Reference Manual, Rev. 1.2
11-8
Freescale Semiconductor
11.6.1
Reservation Protocol
The reservation protocol operates under the following assumptions:
•
Each processor has at most 1 reservation flag
•
A lwarx instruction sets the reservation flag
•
Another lwarx instruction by same processor clears the reservation flag related to a previous lwarx
instruction and sets again the reservation flag
•
A stwcx instruction by the same processor clears the reservation flag
•
A store instruction by the same processor does not clear the reservation flag
•
Some other processor (or other mechanism) store to an address with an existing reservation clears
the reservation flag
•
In case the storage reservation is lost, it is guaranteed that stwcx will not modify the storage
11.6.2
L2U Reservation Support
The L2U is responsible for handling the effects of reservations on the L-bus and the U-bus. For the L-bus
and the U-bus, the L2U detects reservation losses.
The reservation logic in the L2U performs the following functions:
•
Snoops accesses to all L-bus and U-bus slaves
•
Holds one reservation (address) for the core
•
Sets the reservation flag when the RPCU issues a load-with-reservation request
The unit for reservation is one word. A byte or half-word store request by another master will clear the
reservation flag.
A load-with-reservation request by the RPCU updates the reservation address related to a previous
load-with-reservation request and sets the reservation flag for the new location. A store-with-reservation
request by the RPCU clears the reservation flag. A store request by the RPCU does not clear the flag. A
store request by some other master to the reservation address clears the reservation flag.
If the storage reservation is lost, it is guaranteed that a store-with-reservation request by the RPCU will not
modify the storage.
The L2U does not start a store-with-reservation cycle on the U-bus if the reserved location on the U-bus
has been touched by another master. The L2U drives the reservation status back to the core.
When the reserved location in the CALRAM on the L-bus is touched by an alternate master, on the
following clock the L2U indicates to the RPCU that the reservation has been touched. On assertion of the
cancel-reservation signal, the RCPU clears the internal reservation bit. If an stwcx cycle has been issued
at the same time, the RCPU aborts the cycle. Software must check the CR0[EQ] bit to determine if the
stwcx instruction completed successfully.
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.
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...