nRF54L15 (NCS 3.2): Excessive current consumption on UART30 when CONFIG_LOG_MODE_IMMEDIATE=n

[xht1987]

nrf54L15 ncs upgraded from 3.0 to 3.2
CONFIG_SERIAL=y
CONFIG_PM_DEVICE=y
CONFIG_PM_DEVICE_RUNTIME=y
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y
CONFIG_LOG=y
CONFIG_LOG_MODE_IMMEDIATE=n
CONFIG_LOG_BACKEND_UART=y
&uart30 {
status = "okay";
zephyr,pm-device-runtime-auto;
};

&uart30_default {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 0)>;
};
group2 {
psels = <NRF_PSEL(UART_RX, 0, 1)>;
bias-pull-up; };

};

&uart30_sleep {

group1 {
psels = <NRF_PSEL(UART_TX, 0, 0)>,

<NRF_PSEL(UART_RX, 0, 1)>;

low-power-enable;

};

};

The minimum power consumption is 155uA. When changed to CONFIG_LOG_MODE_IMMEDIATE=y, the power consumption can reach 4uA. When CONFIG_LOG_MODE_IMMEDIATE=n, the power consumption is normally 4uA in NCS3.0. Starting with NCS3.2, the serial port seems to be unable to enter low power mode.

[Kazi Afroza Sultana]

Hello,

I have read a previous case (+) How to use low-power UART demos other than lpuart - Nordic Q&A - Nordic DevZone - Nordic DevZone waht you can look at.

Besides setting the CONFIG_SERIAL=n in the prj.conf file you can add the following code 

#include <zephyr/pm/device.h>
static const struct device* uart_dev = DEVICE_DT_GET(DT_CHOSEN(zephyr_console));
err = pm_device_action_run(uart_dev, PM_DEVICE_ACTION_SUSPEND);

[xht1987]

It is not that I no longer need the UART; rather, I would like it to function as it did prior to SDK 3.0—outputting logs via the serial port whenever there is log activity, and subsequently entering a low-power mode once the log output is complete.

[Kazi Afroza Sultana]

Hello,

I have gone through an old case which ((+) Interrupt-driven UART doesn't work with PM_DEVICE_RUNTIME - Nordic Q&A - Nordic DevZone - Nordic DevZone)shows when CONFIG_PM_DEVICE_RUNTIME is set , it may break some drivers after changing NCS version changed. I am not quite sure that could be the issue for  keeping peripheral constantly enabled by UART driver/ logging backend.

So setting CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=n can make it assure that it's not enabled in the application.

Also you want to keep the serial terminal. You can try the following configs

# This is for Logging
CONFIG_LOG=y
CONFIG_LOG_MODE_DEFERRED=y          
CONFIG_LOG_BACKEND_UART=y

# System power management
CONFIG_PM=y
CONFIG_POWEROFF=y

# Device PM; this is the major part where you need to unset the SHIM config
CONFIG_PM_DEVICE=y
CONFIG_PM_DEVICE_RUNTIME=y

CONFIG_UART_NRFX_UARTE_LEGACY_SHIM=n
CONFIG_UART_ASYNC_API=y

# for serial output
CONFIG_SERIAL=y
CONFIG_CONSOLE=n
CONFIG_UART_CONSOLE=n

You can omit adding the UART device suspend code I said before.

Can you try this and measure the current and let us know?

Thanks.

BR

Kazi