Cpburst; Table 8-2 Cpburst Encoding - ARM ARM926EJ-S Technical Reference Manual

8.7

CPBURST

ARM DDI0198D
The CPBURST signal is used by the external coprocessor to indicate the number of
words to be transferred in an LDC or STC operation. CPBURST is used by the
ARM926EJ-S memory system to optimize LDC/STC instructions that access either
noncachable or nonbufferable regions of memory. The encoding of CPBURST is
shown in Table 8-2.
The encoding for a single word transfer and an unknown number of transfers is the
same. If CPBURST is set to b0000 for an STC or LDC operation, and this results in an
access to either a noncached or nonbuffered region of memory, then any resultant AHB
bus transfers are performed as individual nonsequential accesses.
CPBURST is driven by external coprocessors in the same cycle as the CHSDE
response. This must be driven to b0000 at all other times. An example of a transfer that
uses CPBURST is shown in Figure 8-9 on page 8-12.
Copyright © 2001-2003 ARM Limited. All rights reserved.
Coprocessor Interface

Table 8-2 CPBURST encoding

Number of words
CPBURST[3:0]
to transfer
b0000 1 word or unknown
b0001 2 words
b0010 3 words
... ...
b1110 15 words
b1111 16 words
8-11