External Bus Interface
MPC561/MPC563 Reference Manual, Rev. 1.2
9-42
Freescale Semiconductor
9.5.10
Storage Reservation
Reservation occurs when a master loads data from memory. The memory location must not be overwritten
until the master finishes processing the data and writing the results back to the reserved location. The
MPC561/MPC563 storage reservation protocol supports a multi-level bus structure. For each local bus,
storage reservation is handled by the local reservation logic.
The protocol tries to optimize reservation cancellation such that an MPC500 processor is notified of
storage reservation loss on a remote bus only when it has issued a conditional storeword (stwcx) cycle to
that address. That is, the reservation loss indication comes as part of the stwcx cycle. This method avoids
the need to have very fast storage reservation loss indication signals routed from every remote bus to every
MPC500 master.
The storage reservation protocol makes the following assumptions:
•
Each processor has, at most, one reservation flag
•
lwarx sets the reservation flag
•
lwarx by the same processor clears the reservation flag related to a previous lwarx instruction and
again sets the reservation flag
•
stwcx by the same processor clears the reservation flag
•
Store by the same processor does not clear the reservation flag
•
Some other processor (or other mechanism) store to the same address as an existing reservation
clears the reservation flag
•
In case the storage reservation is lost, it is guaranteed that stwcx will not modify the storage
The reservation protocol for a single-level (local) bus is illustrated in
. The protocol assumes
that an external logic on the bus carries out the following functions:
•
Snoops accesses to all local bus slaves
•
Holds one reservation for each local master capable of storage reservations
•
Sets the reservation when that master issues a load and reserve request
•
Clears the reservation when some other master issues a store to the reservation address
Summary of Contents for MPC561
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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...