Missing an example to set low power states on Pico 2

[ullibak]

I try to enable the low power states on the Pico 2 but without any success. If I read the documentation correctly, power state P1.7 equals 1111 in binary or 15 decimal. Using

uint32_t ps = 15;
int i = powman_set_power_state(ps);

returns 0 for i which means that the function was performed successfully, but adding

printf("Power State: %d\n", powman_get_power_state ());

right after the code above returns 0, so that somehow, the power state has not changed.

I am sure that I am missing something so it would be nice to add an example that demonstrates how the Pico 2 could be sent to a low power state for a definded amount of time.

Thanks!

[lurch]

Perhaps raspberrypi/pico-playground#48 is what you're looking for? Although I'm afraid I'm not sure if "sleep" and "low power" are actually separate things? 🤷

[ullibak]

The sleep demo you mention uses some "tricks" to save power an I can not see how the new power management states of the RP2350 are used. Reading the specs of the RP2350 and the SDK documentation, I was expecting some much more high level approach to send the RP2350 into an low power state. So a simple example in the SDK would be very helpful.

[peterharperuk]

Those sleep examples don't use powman. I don't think we're going to add a powman example. We want to add a new API for low power but ran out of time before the Pico 2 sdk update. In the meantime there are a couple powman examples here peterharperuk@35db8fc

[ullibak]

Hi
Thanks a lot! The powerman examples are really useful and helped a lot to undestand how to use the new power states.
With the timer example, I am able to lower the power consumption to 0.7 mA during sleep. This is good, but still a multiple of the values given in section 4.1.1 of the data sheet:

https://datasheets.raspberrypi.com/pico/pico-2-datasheet.pdf

Power state P1.7 should draw only 0.148 mA.

In the data sheet they describe the current consumption measurements with

All externally accessible GPIOs, SWD and SWCLK are unconnected. The RP2350’s USB PHY has been powered down,
and the DP and DM pull-downs enabled prior to entering the low power state. The USB cable remains connected to a
host computer.

I have no GPIO connected. But I do not know how to power down the USB PHY and how to enable the DP and DM pull-downs.

Does anyone know how to do this?

Thanks!

[lurch]

But I do not know how to power down the USB PHY

That's probably related to section 6.1.4. in https://datasheets.raspberrypi.com/rp2350/rp2350-datasheet.pdf ? However note that it says "This supply must always be provided, even in applications where the USB PHY is never used."

[ullibak]

Thanks, lurch
Section 6.1. describes the different power supplies needed to run the RP2350 chip. But from the text in section 4.1.1. of the Pico 2 data sheet I conclude that there must be a way to power down USB PHY using a software command.

[peterharperuk]

I will try and find out where those numbers come from. The best I can achieve is .29mA, by powering the device with 3V3 and disconnecting everything (USB, UART, SWD) and removing R10 (at your own risk)

[ullibak]

I can get 0.36 mA when connecting a Li-Ion battery (4.2V) to VSYS and leave everything else disconnected.

In section 1.2.2. of the RP2350 data sheet all the pins are described. The description for the USP_DM and USB_DP pins is:

USB controller, supporting Full Speed device and Full/Low Speed host. A 27Ω series termination
resistor is required on each pin, but bus pullups and pulldowns are provided internally. These pins
can be used as software-controlled GPIOs, if USB is not required.

So there is a way to connect internal pulldowns via software commands. But I could not figure out how to to this.

[peterharperuk]

I can reproduce the power numbers in the datasheet with this commit. Make sure you disconnect everything except for 5v into vsys peterharperuk@7dccd00

[tannewt]

I can reproduce the power numbers in the datasheet with this commit. Make sure you disconnect everything except for 5v into vsys peterharperuk@7dccd00

Nice! How are others expected to reproduce this? Copy that code? Use a SDK API?

[ullibak]

Thanks a lot!
Li-Ion battery (4.11 V) connected to VSYS. Pico draws 150.8 microamps during low power. This is 620 microwatts. Great!!!

@tannewt: You find the code in https://github.com/peterharperuk/pico-examples/tree/35db8fc31d322de2bcac641d9b6b0f6fdb73062c/powman

it is emedded in the example directory tree there. You can copy th whole directory tree and substitute pico-examples.

I use a simplified standalone version, see attached zip file.
powman_standalone.zip

copy these two files plus pico_sdk_import.cmake and pico_extras_import_optional.cmake from the Pico SDK into a directory and you should be able to compile as usual. I use VS Code with the Pico Extension.

[peterharperuk]

There might be a non-hardware API in future. So you can wait for that or else you'll have to copy that code.

[matsobdev]

Powering flash down will allow to save extra 10 uA (mileage may vary), but then when starting from flash, it should be powered up (or released from power down): raspberrypi/pico-sdk#2111