Motorola MPC533 Reference Manual page 1052

Operation Modes
Whenever the IMPU detects access violation, the following actions are taken:
1. The request forwarded to the BIU is canceled
2. The RCPU is informed that the requested address caused an access violation by
exception request.
However, if the required address contains a show cycle attribute, the BIU delivers the
access onto the U-bus to obtain program tracking.
The exception vector (address) that the RCPU issues for this exception has a 0x1300 offset
in the RCPU exception vector table. The access violation status is provided in the RCPU
SRR1 special purpose register. The encoding of the status bits is as follows:
• SRR1 [1] = 0
• SRR1 [3] = Guarded storage
• SRR1 [4] = Protected storage or compression violation
• SRR1 [10] = 0
Only one bit is set at a time.
G.3.2 Vocabulary Table Storage Operation
The uses DECRAM for decompressor vocabulary tables (VT1 and VT2) storage in
decompression on mode. The ICDU utilizes DECRAM as separately accessed -Kbyte
RAM arrays (16 bits wide) that are accessed via internal ICDU buses. The VTs should be
loaded before the decompression process starts. In order to allow decompression, the
DECRAM must be disabled for the U-bus accesses after VTs and decompressor class
configuration registers (DCCRs) are initialized.
G.3.3 READI Compression
Setting BBCMCR[DECOMP_SC_EN] when decompression is enabled allows READI
(Chapter 22, "READI
BBCMCR[DECOMP_SC_EN] should not be set if there is no intention to use compressed
code, as it will degrade U-bus performance. The show cycle may be delayed by one clock
by the USIU if the show cycle occurs after an external device read cycle. Refer to
Section 22.1.5.2, "Compressed Code Mode Guidelines."
The ICTRL register must be programmed such that a show cycle will be performed for all
changes in the program flow (ISCTL field = 0b01), or the PTM bit must be set and ISCTL
must be set to a value other than 0b11. (See Table G-13.)
G-20
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Module") to
MPC533 Reference Manual
track the compressed code.
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