Port, board and/or hardware

rp2 on RPI PICO2

MicroPython version

MicroPython v1.24.0-dirty on 2025-01-09; Raspberry Pi Pico2 with RP2350
Also on latest version v1.25.preview commit 495ce91 and 1.24.1

Reproduction

To get some insight on the problem I added some debug code to mp_hal_delay_us() in mphalport.c.

here is a diff of my changes:

git diff mphalport.c
diff --git a/ports/rp2/mphalport.c b/ports/rp2/mphalport.c
index 3f5015162..4a9fc1c50 100644
--- a/ports/rp2/mphalport.c
+++ b/ports/rp2/mphalport.c
@@ -151,10 +151,13 @@ void mp_hal_delay_us(mp_uint_t us) {
 void mp_hal_delay_ms(mp_uint_t ms) {
     mp_uint_t start = mp_hal_ticks_ms();
     mp_uint_t elapsed = 0;
+    mp_uint_t loop_count = 0;
     do {
         mp_event_wait_ms(ms - elapsed);
         elapsed = mp_hal_ticks_ms() - start;
+       ++loop_count;
     } while (elapsed < ms);
+    mp_printf(MP_PYTHON_PRINTER, "delay loop_count=%d\n", loop_count);
 }
 
 void mp_hal_time_ns_set_from_rtc(void) {

To build the 1.24.0 micropython (commit f212bbe) with my debug code I did:

git clone https://github.com/micropython/micropython.git micropython-direct-clone
cd micropython-direct-clone
git checkout f212bbe
make -C mpy-cross -j4
cd ports/rp2
make -j4 BOARD=RPI_PICO submodules
make -j4 BOARD=RPI_PICO2 submodules
make -j4 BOARD=RPI_PICO2
make -j4 BOARD=RPI_PICO

Expected behaviour

On RPI PICO we see the expected behavior. My code counts the number of times the loop in mp_hal_delay_ms runs.

MicroPython v1.24.0-dirty on 2025-01-09; Raspberry Pi Pico with RP2040
Type "help()" for more information.
>>> from time import sleep_ms
>>> sleep_ms(1000)
delay loop_count=2

Two times around the loop for a one second sleep is reasonable.

Observed behaviour

On RPI 2350 we see:

MicroPython v1.24.0-dirty on 2025-01-09; Raspberry Pi Pico2 with RP2350
Type "help()" for more information.
>>> from time import sleep_ms
>>> sleep_ms(1000)
delay loop_count=200242

See the loop executed 200,242 times for a one second sleep.
Basically we have a busy wait loop.

Additional Information

This issue likely does not impact users.
But it does indicate a RP2350 specific bug.

I care about this behavior because I have code modifying the RP2040 or RP2350 SLEEP_EN0 and SLEEP_EN1 registers to disable hardware blocks while the chip is sleeping.
You can see that code in my github repo RP2-PowerControl,
The intent is to reduce power consumption.

This works fine on the PICO and PICO W with RP2040. I see the current drop by a significant amount.
I do not see any current reduction on PICO2 with RP2350.
But, if I modify registers WAKE_EN0 and WAKE_EN1 to disable hardware while running I do see some power reduction.

I assert this is because the ARM core keeps executing in the busy wait loop.
Since the processor is not sleeping no hardware is disabled and therefore no power reduction.

I would love to investigate more on my own, but I am stuck.
Possibly @projectgus would have insights.
He has been doing work related to softtimer and support for RP2350.

Code of Conduct

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