MPC555
/
MPC556
BURST BUFFER
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
4-16
4.6.4 BBC Module Configuration Register (BBCMCR)
deter-
mines whether the BBC operates burst cycles or not. Burst requests are enabled only
when the BE bit is set.
NOTE
The negated state of the BE bit is useful mainly when the RCPU core
runs in serialized mode. (Refer to
for the ICTRL register.)
4.4.7 Error Detection
If the IMPU detects access violation, the following actions must be taken:
1. Cancel the request that was forwarded to the burst buffer controller
2. Inform the RCPU core that the requested address generated an exception
If the required address contains show cycle or program trace attributes, than the BBC
delivers the access onto the U-bus even if the request is cancelled (due to the excep-
tion it caused).
The way the IMPU notifies the RCPU core for an interrupt is by feeding error informa-
tion into four bits (1, 3, 4 and 10) in the SRR1 register in the core. Only one bit is set
at a time. The exception vector (address) that the core issues for this event is 0xnnn0-
1300. The encoding of the status bits is as follows:
• SRR1 = 0
• SRR3 = Guarded storage.
• SRR4 = Protected storage.
• SRR10 = 0
4.5 Exception Table Relocation
The BBC has the ability to relocate the exception table. Exception table relocation is a
feature to save memory space in the exception table. See
for normal operation of the exception vector table. This is done by mapping ex-
ceptions to be separated by eight bytes instead of 256 bytes (see
). The re-
location feature maps the exception table into the internal memory space of the
MPC555 / MPC556 and requries MSR[IP] = 1. This feature is important in multi-
MPC555 / MPC556 systems, where more than one MCU can have internal exception
tables with the same exception addresses issued by the RCPU.
The relocation feature also saves the wasted space between exception table entries
when each exception entry contains only a branch instruction to the exception routine,
which is located elsewhere.
If exception relocation is enabled (ETRE bit is set in the BBCMCR), all exception rou-
tines (except the reset exception routine) can be controlled to either remain in the low-
er addresses of the memory (base a exception offset) BBCMCR[OERC] = 0
or to be relocated to memory (base a 32 Kbytes) by setting BBCMCR[OERC]
= 1. The reset exception routine location is fixed in memory (base a the reset
exception offset) and can not be relocated.
See
4.6.4 BBC Module Configuration Register (BBCMCR)
for programming details.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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