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ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 9-13
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9.3.3 Linefills
Loads and instruction fetches from Normal, Cacheable memory that do not hit in the cache
generate a cache linefill when the appropriate cache is enabled. Table 9-12 shows the values of
ARADDRM, ARBURSTM, ARSIZEM, and ARLENM for cache linefills.
9.3.4 Cache line write-back (eviction)
When a valid and dirty cache line is evicted from the d-cache, a write-back of the data must
occur. Table 9-13 shows the values of AWADDRM, AWBURSTM, AW S IZE M, and
AWLENM for cache line write-backs, over the AXI master interface.
9.3.5 Non-cacheable reads
Load instructions accessing Non-cacheable Normal memory generate AXI bursts that are not
necessarily the same size or length as the instruction implies. In addition, if the data to be read
is contained in the store buffer, the instruction might not generate an AXI read transaction at all.
The tables in this section give examples of the types of AXI transaction that might result from
various load instructions, accessing various addresses in Non-cacheable Normal memory. They
are provided as examples only, and are not an exhaustive description of the AXI transactions.
Depending on the state of the processor, and the timing of the accesses, the actual bursts
generated might have a different size and length to the examples shown, even for the same
instruction.
Table 9-14 shows possible values of ARADDRM, ARBURSTM, ARSIZEM, and ARLENM
for an
LDRH
from bytes 0-7 in Non-cacheable Normal memory.
Table 9-12 Linefill behavior on the AXI interface
Address[4:0]
a
a. These are the bottom five bits of the address of the access that cause the linefill, that
is, the address of the critical word.
ARADDRM ARBURSTM ARSIZEM ARLENM
0x00
-
0x07 0x00
Wrap 64-bit 4 data transfers
0x08
-
0x0F 0x08
Wrap 64-bit 4 data transfers
0x10
-
0x17 0x10
Wrap 64-bit 4 data transfers
0x18
-
0x1F 0x18
Wrap 64-bit 4 data transfers
Table 9-13 Cache line write-back
AWADDRM[4:0] AWBURSTM AWSIZEM AWLENM
0x00
Incr 64-bit 4 data transfers
Table 9-14 LDRH from Non-cacheable Normal memory
Address[2:0] ARADDRM ARBURSTM ARSIZEM ARLENM
0x0
(byte 0)
0x00
Incr 16-bit 1 data transfer
0x1
(byte 1)
0x00
Incr 32-bit 1 data transfer
0x2
(byte 2)
0x00
Incr 64-bit 1 data transfer
0x3
(byte 3)
0x03
Incr 32-bit 2 data transfers