MPC555
/
MPC556
L-BUS TO U-BUS INTERFACE (L2U)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
11-8
If the storage reservation is lost, it is guaranteed that a store-with-reservation request
by the CPU will not modify the storage.
The L2U does not start a store-with-reservation cycle on the U-bus if the reserved lo-
cation on the U-bus has been touched by another master. The L2U drives the reser-
vation status back to the core.
When the reserved location in the SRAM on the L-bus is touched by an alternate mas-
ter, on the following clock, the L2U indicates to the CPU 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.
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 ter-
mination 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 CPU core reserves a memory location, the L2U module is responsible for
snooping L-bus and U-bus for possible intrusion of the reserved location. Under cer-
tain circumstances, the L2U depends on the USIU or the UIMB to provide status of res-
ervation on external bus and the IMB3 respectively.
lists all reservation protocol cases supported by the L2U snooping logic.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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