MPC555
/
MPC556
EXTERNAL BUS INTERFACE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
9-41
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
Figure 9-29 Reservation On Local Bus
The MPC555
/ MPC556 samples the CR line at the rising edge of CLKOUT.
When this
signal is asserted, the reservation flag is reset.
The EBI samples the logical value of the reservation flag prior to externally starting a
bus cycle initiated by the RCPU
stwcx
instruction. If the reservation flag is set, the EBI
begins with the bus cycle. If the reservation flag is reset, no bus cycle is initiated ex-
ternally, and this situation is reported to the RCPU.
The reservation protocol for a multi-level (local) bus is illustrated in
. The
system describes the situation in which the reserved location is sited in the remote
bus.
S
R
Reservation
Logic
External Bus
Interface
lwarx
Q
Enab
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ex
tern
al
st
wc
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ss
CR
External Bus
Master
Bus
ADDR[0:29]
CR
CLKOUT
AT[0:3], RSV, R/W, TS
MPC555 /
MPC556
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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