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
• 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
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