PXA27X睡眠唤醒问题

一个要命的睡眠唤醒问题。谨此记之：(来自Intel? PXA27x Processor Family
Specification Update)

E50. POWER MANAGER: The processor does not exit from sleep/deepsleep
mode.
Problem: The processor is exhibiting a problem when waking up from sleep and deep-sleep mode.
Specifically, the issue is a race condition between clocks in the processor's sleep/deepsleep
wakeup circuitry. When the processor begins to wake from sleep/deep-sleep mode,
a reset to the clock unit de-asserts while the internal power and ground supplies to the
wakeup circuitry are not yet stable. The effect is that parts of the clock unit will be in an
unknown state after the reset has been de-asserted. In most cases, the race condition
will end successfully without de-asserting the reset too early and the issue will not be
seen. However, in a small number of parts, the reset de-asserts too early, thus causing the
issue.
Implication: Early release of the reset prior to a good, stable power and ground supply can lead to
unpredictable values during wakeup and can result in the processor stopping execution.
The Erratum is also manufacturing process dependent and intermittent, so only a small
percentage of devices are ultimately affected.
Workaround: Intel has found that keeping VCC_Core powered during sleep mode seems to prevent the
predictable behavior because it helps keep the correct state of the wakeup circuitry, even
when the reset to the wakeup circuitry is de-asserted early. Additional testing has also
shown that entering sleep mode at 91 MHz with VCC_Core at 0.95V (+/- 5%), but then
grounding VCC_Core during sleep helps to alleviate the issue in a large number of cases,
but not all. Finally, the processor's watchdog timer can be implemented to reset the
processor, if the failure occurs. This gives customers the ability to gracefully handle a
system failure due to this erratum. Use of the potential workarounds can help greatly
reduce or possibly eliminate the occurrence of the erratum. Details of these workarounds
can be found in the following Application Note: Sleep/Deep-Sleep Exit Procedure for the
Intel? PXA27x Processor Family.
Status: Fixed