ARM Cortex-A15 MPCore Processor Technical Reference Manual

Functional Description2.3 Clocking and resetsThis section describes the clocks and resets of the processor in:• Clocks.• Resets on page 2-11.2.3.1 ClocksThe processor has the following clock inputs:CLKThis is the main clock of the Cortex-A15 MPCore processor. All processors, theshared L2 memory system logic, the GIC, and the Generic Timer are clocked witha distributed version of CLK.PCLKDBG This is the APB clock that controls the Debug APB, CTI and CTM logic in thePCLKDBG domain. PCLKDBG is asynchronous to CLK.The processor has the following clock enable inputs:ACLKENM The AXI master interface is a synchronous AXI interface that can operate at anyinteger multiple that is equal to or slower than the main processor clock, CLK,using the ACLKENM signal. For example, you can set the CLK to ACLKMfrequency ratio to 1:1, 2:1, or 3:1, where ACLKM is the AXI master clock.ACLKENM asserts one CLK cycle prior to the rising edge of ACLKM.Software can change the CLK to ACLKM frequency ratio dynamically usingACLKENM.Figure 2-2 shows a timing example of ACLKENM that changes the CLK toACLKM frequency ratio from 3:1 to 1:1.1 CLKcycle1 CLKcycleCLKACLKENMACLKENM asserts one CLK cyclebefore the rising edge of ACLKMACLKMCLK:ACLKM = 3:1 CLK:ACLKM = 1:1Figure 2-2 ACLKENM with CLK:ACLKM ratio changing from 3:1 to 1:1NoteFigure 2-2 shows the timing relationship between the AXI master clock,ACLKM and ACLKENM, where ACLKENM asserts one CLK cycle beforethe rising edge of ACLKM. It is important that the relationship betweenACLKM and ACLKENM is maintained.ACLKENS ACP is a synchronous AXI slave interface that can operate at any integer multiplethat is equal to or slower than the main processor clock, CLK, using theACLKENS signal. For example, the CLK to ACLKS frequency ratio can be 1:1,2:1, or 3:1, where ACLKS is the AXI slave clock. ACLKENS asserts one CLKcycle before the rising edge of ACLKS. The CLK to ACLKS frequency ratio canbe changed dynamically using ACLKENS.ARM DDI 0438I Copyright © 2011-2013 ARM. All rights reserved. 2-8ID062913Non-Confidential