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Problem with disabling the MPLL

Question asked by Craig Hillis on Mar 8, 2016
Latest reply on Mar 16, 2016 by Craig Hillis

When using a 26 MHz crystal, we can disable the MPLL to go to sleep mode. When the crystal is replaced with a 26 MHz oscillator, the MPLL is not reliably disabled.


The Reference manual states:


The conditions to be satisfied before the PLL Clock Controller actually turns off the MPLL are as




1. Clock Controller module has successfully mastered the system bus.


2. The A9P_CLK_OFF signal from the ARM9 Platform is active.


3. SDRAM controller has successfully placed the external SDRAM into Self-Refresh mode.


4. After the above conditions are satisfied, the countdown based on the value in the SD_CNT field


will be initiated.


5. SD_CNT countdown completes.


What could prevent the Clock Controller module from successfully mastering the system bus?