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nrf: port: add memory barrier before wfi

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ARM recommends issuing a DSB instruction propr to issuing WFI, as it is
required on many parts suchas Cortex-M7. This is effectively a no-op on
the Cortex-M4 used in most NRF parts, however it ensures that we won't
be surprised when new parts come out.

See
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dai0321a/BIHICBGB.html
for more information.

Signed-off-by: Sean Cross <sean@xobs.io>
This commit is contained in:
Sean Cross 2020-05-21 21:46:37 +08:00
parent 77cf4dce8f
commit fd4ef233c6
1 changed files with 3 additions and 1 deletions
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4
ports/nrf/supervisor/port.c
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@ -273,8 +273,10 @@ void port_sleep_until_interrupt(void) {
// available, even though the actual handler won't fire until
// we re-enable interrupts.
common_hal_mcu_disable_interrupts();
if (!tud_task_event_ready())
if (!tud_task_event_ready()) {
__DSB();
__WFI();
}
common_hal_mcu_enable_interrupts();
}
}