ARM Technical Support Knowledge Articles

What can cause ARM11 not to enter standy mode when WFI instruction is executed?

Applies to: ARM11 processors

Scenario

When executing Wait For Interrupt CP15 operation at run-time, sometimes the STANDBYWFI signal is not asserted and sometimes it is. Could you please tell me the possible/probable causes that might result in malfunction of Wait For Interrupt CP15 operation?

Answer

If you have a pending imprecise abort, this will prevent the core from entering standby state. This is the designed behaviour so is correct, unfortunately it is not documented in the TRM. The action you should take is to handle the abort before entering standby, so you should clear the A bit, this will result in an abort exception, before executing the WFI instruction.
 

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