Functional Description
ARM DDI 0500D
Copyright © 2013-2014 ARM. All rights reserved.
2-10
ID021414
Non-Confidential
ACLKENM
This signal is present only if the master interface is configured to use the ACE protocol. The
master interface supports integer ratios of the
CLKIN
frequency, for example 1:1, 2:1, 3:1.
These ratios are configured through external clock enable signals. In all cases AXI transfers
remain synchronous. The ACE master interface includes the
ACLKENM
clock enable signal.
ACLKENM
asserts one
CLKIN
cycle before the rising edge of the external ACE clock signal,
ACLKM
. If you change the
CLKIN
to
ACLKM
frequency ratio, you must change
ACLKENM
correspondingly.
Figure 2-3
shows a timing example of
ACLKENM
that changes the
CLKIN
to
ACLKM
frequency ratio from 3:1 to 1:1.
Figure 2-3 ACLKENM with CLKIN:ACLKM ratio changing from 3:1 to 1:1
Note
•
Figure 2-3
shows the timing relationship between the AXI master clock,
ACLKM
and
ACLKENM
, where
ACLKENM
asserts one clock cycle before the rising edge of
ACLKM
. It is important that the relationship between
ACLKM
and
ACLKENM
is
maintained.
•
If there are any physical effects that could occur while changing the clock frequency,
ARM recommends that the clock ratio is changed only while the
STANDBYWFIL2
output of the processor is asserted.
•
The input signal
ACLKENM
exists in the Cortex-A53 processor if it is configured to
include the ACE interface.
ACLKENS
This signal is present only if the processor is configured with the ACP slave interface. The slave
interface supports integer ratios of the
CLKIN
frequency, for example 1:1, 2:1, 3:1. These
ratios are configured through external clock enable signals. In all cases AXI transfers remain
synchronous. The ACP slave interface includes the
ACLKENS
clock enable signal.
ACLKENS
asserts one
CLKIN
cycle before the rising edge of the external ACP clock signal,
ACLKS
. If you change the
CLKIN
to
ACLKS
frequency ratio, you must change
ACLKENS
correspondingly.
Figure 2-4 on page 2-11
shows a timing example of
ACLKENS
that changes the
CLKIN
to
ACLKS
frequency ratio from 3:1 to 1:1.
ACLKM
ACLKENM
asserts one
CLKIN
cycle before the rising edge of
ACLKM
1
CLKIN
cycle
CLKIN
:
ACLKM
= 3:1
CLKIN
:
ACLKM
= 1:1
ACLKENM
CLKIN
1
CLKIN
cycle