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
AWSIZE
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
AWLOCK
signals are not present.
•
ARQOS
and
AWQOS
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
.
—
AWSIZE
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
.
—
AWSIZE
and
AWBURST
assume values of
0b100
and INCR respectively.
—
WSTRB
can take any value.