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MPC555
/
MPC556
EXTERNAL BUS INTERFACE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
9-42
Figure 9-30 Reservation On Multilevel Bus Hierarchy
In this case, the bus interface block implements a reservation flag for the local bus
master. The reservation flag is set by the bus interface when a load with reservation is
issued by the local bus master and the reservation address is located on the remote
bus. The flag is reset when an alternative master on the remote bus accesses the
same location in a write cycle. If the MPC555
/ MPC556 begins a memory cycle to the
previously reserved address (located in the remote bus) as a result of an
stwcx
in-
struction, the following two cases can occur:
• If the reservation flag is set, the buses interface acknowledges the cycle in a nor-
mal way
• If the reservation flag is reset, the bus interface should assert the KR. However,
S
R
Buses
Interface
External Bus
Interface
Q
KR
External Bus (Local Bus)
AT[0:3], RSV, R/W, TS
ADDR[0:29]
Remote Bus
A Master in the Remote Bus Write
to the Reserved Location
Local Master Accesseses with
to Remove Bus Address
lwarx
MPC555 /
MPC556
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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