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0.0.1
Burst Operation of the BBC
The 's BBC may initiate and handle burst accesses on the U-bus. The BBCMCR[BE] bit
determines whether the BBC operates burst cycles or not. Burst requests are enabled when
the BE bit is set. The BBC handles non-wrap-around bursts with up to 4 data beats on the
internal U-bus. Refer to Section 27.6.2.1, "BBC Module Configuration Register
(BBCMCR)."
The burst operation in the is useful if a user system implements
burstable memory devices on the external bus. Otherwise the
mode will cause performance degradation when running code
from external memory.
When the RCPU runs in serialized mode it is recommended
that bursts be disabled by the BBC to speed up operation.
Burst operation in decompression off and debug modes are
disabled regardless of BBCMCR[BE] bit setting.
The BBC burst should be turned off if the USIU burst feature
is enabled.
0.0.2
Access Violation Detection
Instruction memory protection is assigned on a regional basis. Default operation of IMPU
is done on a global region. The IMPU has control registers which contain the following
information: region protection on/off, region base address, size and access permissions.
Protection logic is activated only if the RCPU MSR[IR] bit is set.
During each fetch request from the RCPU core to instruction memory, the address is
compared to a value in the region base address of enabled regions. Any address matching
the specific region within its appropriate size as defined in the region attribute register sets
a match indication.
When more than one match indication occurs, the effective region is the region with the
highest priority. Priority is determined by region number. The lowest region number has the
highest priority and the global region has lowest priority.
When no match happens, the effective region is the global region.
The region attribute registers contain the region protection fields: PP, G, and CMPR. The
protection fields are compared to address attributes issued by the RCPU. If the access is
permitted, the address is passed to the BIU and further to the U-bus.
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
NOTE
Appendix G. MPC534 Compression Features
Operation Modes
G-19
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