Level 2 Memory System
ARM DDI 0500D Copyright © 2013-2014 ARM. All rights reserved. 7-19
ID021414 Non-Confidential
7.7 ACP
The optional Accelerator Coherency Port (ACP) is implemented as an AXI4 slave interface
with the following restrictions:
• 128-bit read and write interfaces.
• ARCACHE and AWCACHE are restricted to Normal, Write-Back,
Read-Write-Allocate, Read-Allocate, Write-Allocate, and No-Allocate memory.
ARCACHE and AWCACHE are limited to the values
0b0111
,
0b1011
, and
0b1111
. Other
values cause a SLVERR response on RRESP or BRESP.
• Exclusive accesses are not supported.
• Barriers are not supported. The BRESP handshake for a write transaction indicates global
observability for that write.
• ARSIZE and AW S IZ E signals are not present and assume a value of
0b100
, 16 bytes.
• ARBURST and AWBURST signals are not present and assume a value of INCR.
• ARLOCK and AW LO C K signals are not present.
• ARQOS and AW Q OS signals are not present.
• ARLEN and AWLEN are limited to values 0 and 3.
This section describes ACP in:
• Transfer size support.
• ACP user signals on page 7-20.
• ACP performance on page 7-20.
7.7.1 Transfer size support
ACP supports the following read-request transfer size and length combinations:
• 64 byte INCR request characterized by:
— ARLEN is
0x03
, 4 beats.
— ARADDR aligned to 64 byte boundary, so ARADDR[5:0] is
0b000000
.
— ARSIZE and ARBURST assume values of
0b100
and INCR respectively.
• 16 byte INCR request characterized by:
— ARLEN is
0x00
, 1 beat.
— ARADDR aligned to 16 byte boundary, so ARADDR[3:0] is
0x0
.
ACP supports the following write-request transfer size and length combinations:
• 64 byte INCR request characterized by:
— AWLEN is
0x03
, 4 beats.
— AWADDR aligned to 64 byte boundary, so AWADDR[5:0] is
0b000000
.
— AW SI ZE and AWBURST assume values of
0b100
and INCR respectively.
— WSTRB for all beats must be the same and either all asserted or all deasserted.
• 16 byte INCR request characterized by:
— AWLEN is
0x00
, 1 beat.
— AWADDR aligned to 16 byte boundary, so AWADDR[3:0] is
0x0
.
— AW SI ZE and AWBURST assume values of
0b100
and INCR respectively.
— WSTRB can take any value.
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