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Cortex-A8 Technical Reference Manual - ARM Information Center

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Clock, Reset, and Power Control<br />

Figure 10-2 shows a change to a 1:1 clock ratio. In this figure, ACLKEN remains asserted,<br />

changing the CLK:ACLK frequency ratio from 4:1 to 1:1.<br />

CLK<br />

ACLKEN<br />

ACLK<br />

10.1.2 Debug clocking using PCLKEN<br />

10.1.3 ATB clocking using ATCLKEN<br />

Figure 10-2 Changing the CLK-to-ACLK ratio from 4:1 to 1:1<br />

All debug logic within the processor operates at an integer multiple of PCLK that is the same<br />

frequency as or slower than the APB clock, PCLK, using PCLKEN. Figure 10-3 shows the<br />

behavior of PCLKEN. In this figure, PCLKEN remains asserted, changing the<br />

PCLK:internal PCLK frequency ratio from 4:1 to 1:1.<br />

PCLK<br />

PCLKEN<br />

Internal PCLK<br />

2 cycles<br />

Figure 10-3 Changing the PCLK-to-internal-PCLK ratio from 4:1 to 1:1<br />

Note<br />

If PCLKEN is not used, then it must be tied HIGH. This results in all state in the debug logic<br />

being clocked by PCLK directly.<br />

All ATB logic within the processor operates at an integer multiple of ATCLK that is the same<br />

frequency as or slower than the ATB clock, ATCLK, using ATCLKEN. Figure 10-4 shows the<br />

behavior of ATCLKEN. In this figure, ATCLKEN remains asserted, changing the<br />

ATCLK:internal ATCLK frequency ratio from 4:1 to 1:1.<br />

ATCLK<br />

ATCLKEN<br />

Internal ATCLK<br />

1 cycle<br />

1 cycle<br />

Figure 10-4 Changing the ATCLK-to-internal-ATCLK ratio from 4:1 to 1:1<br />

Note<br />

If ATCLKEN is not used, then it must be tied HIGH. This results in all state in the ATB logic<br />

being clocked by ATCLK directly.<br />

<strong>ARM</strong> DDI 0344K Copyright © 2006-2010 <strong>ARM</strong> Limited. All rights reserved. 10-3<br />

ID060510 Non-Confidential

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