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Commit42d0b28

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rp2,docs: Stop machine.idle() blocking indefinitely, update docs.
When rp2 port went tickless the behaviour of machine.idle() changed asthere is no longer a tick interrupt to wake it up every millisecond. On aquiet system it would now block indefinitely. No other port does this.A lot of existing code (i.e. micropython-lib lps22h, lcd160cr sensordrivers, lora sync_modem driver, usb-device-hid) call machine.idle() insidea tight loop that is polling some condition. This reduces the power usagecompared to constantly looping, but can be faster than calling a sleepfunction. However there's not always an interrupt before the condition theyare polling for, so it's difficult to restructure this code ifmachine.idle() doesn't have any upper limit on execution time.Also changes the machine module documentation to explain the new behaviourand recommended usage. I believe all ports will pause for at most 1ms now,and suggest this is good behaviour to stick with.Adds a test case for this. Test case fails on master, and also fails on rp2port without the fix for WFE that was found while testing this change.This work was funded through GitHub Sponsors.Signed-off-by: Angus Gratton <angus@redyak.com.au>
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‎docs/library/machine.rst

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@@ -127,14 +127,20 @@ Power related functions
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..function::idle()
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Gates the clock to the CPU, useful to reduce power consumption at any time during
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short or long periods. Peripherals continue working and execution resumes as soon
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as any interrupt is triggered (on many ports this includes system timer
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interrupt occurring at regular intervals on the order of millisecond).
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Gates the clock to the CPU, useful to reduce power consumption at any time
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during short or long periods. Peripherals continue working and execution
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resumes as soon as any interrupt is triggered, or at most one millisecond
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after the CPU was paused.
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It is recommended to call this function inside any tight loop that is
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continuously checking for an external change (i.e. polling). This will reduce
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power consumption without significantly impacting performance. To reduce
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power consumption further then see the:func:`lightsleep`,
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:func:`time.sleep()` and:func:`time.sleep_ms()` functions.
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..function::sleep()
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..note::This function is deprecated, use `lightsleep()` instead with no arguments.
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..note::This function is deprecated, use:func:`lightsleep()` instead with no arguments.
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..function::lightsleep([time_ms])
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deepsleep([time_ms])

‎ports/rp2/modmachine.c

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@@ -103,7 +103,7 @@ static void mp_machine_set_freq(size_t n_args, const mp_obj_t *args) {
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}
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staticvoidmp_machine_idle(void) {
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__wfe();
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MICROPY_INTERNAL_WFE(1);
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}
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staticvoidmp_machine_lightsleep(size_tn_args,constmp_obj_t*args) {

‎tests/extmod/machine_idle.py

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@@ -0,0 +1,41 @@
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try:
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importmachine
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importtime
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machine.idle
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# skip for ports which don't have Pin class. Unix port uses sched_yield for
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# idle, on a quiet system this always resumes immediately.
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machine.Pin
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except:
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print("SKIP")
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raiseSystemExit
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# Verify that machine.idle() resumes execution within 0.1 and 1.1ms (should be
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# 1ms max but allowing for some overhead).
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#
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# (A minimum sleep time for machine.idle() isn't specified but in a system like
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# this with no active interrupts then we should expect some idle time before
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# resuming. If it's consistently resuming immediately then that indicates a bug
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# is preventing proper idle.)
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#
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# Verification uses the average idle time, as individual iterations will always
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# have outliers due to interrupts, scheduler, etc.
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ITERATIONS=500
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total=0
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for_inrange(ITERATIONS):
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before=time.ticks_us()
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machine.idle()
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total+=time.ticks_diff(time.ticks_us(),before)
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total/=1000# us to ms
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average=total/ITERATIONS
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# print(f"Total {total}ms average {average}ms") # uncomment for debug
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if0.1<average<1.1:
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print("PASS")
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else:
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print(f"Total{total}ms average{average}ms, out of spec")

‎tests/extmod/machine_idle.py.exp

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PASS

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