UART power consumption Zephyr NRF52833

[sixaxix9]

Hi all!

I am developing an application with Zephyr (commit b21a91e46833cfcf4f2bda9e3e0f9d8c2150882e) on nrf52833 and a Ublox SARA R5. I communicate with the module via the UART and I am now trying to optimise the power consumption. When I run the code with the UART1 status 'disabled' on the devicetree I get the expected power consumption (uA), but when I try to enable it (even without using it, just setting the status to "okay") the power consumption stays on the mA range.

I have the following settings enabled:

CONFIG_PM=y
CONFIG_PM_DEVICE=y
CONFIG_PM_DEVICE_RUNTIME=y

and I think the power management is working fine without the UART. I tried to force the UART to sleep with the following code:

int error = pm_device_state_set(DEVICE_DT_GET(DT_NODELABEL(uart1)), PM_STATE_SOFT_OFF, NULL, NULL);

But the function return a -134 error, which I think is a "non supported" error. Moreover, I tried to be sure that the UART has no IRQ or RX active, running this code:

uart_irq_tx_disable(uart);
uart_irq_rx_disable(uart);
int error = uart_rx_disable(uart);

but the consumption doesn't change and the 'uart_rx_disable' returns -14, which if I am not mistaken means the UART RX is already disabled.

Do you have any pointers on how to turn off the UART at runtime?

Thanks a lot!

[sixaxix9]

Update:

After some digging in the Zephyr power management code I found out that I should be using `pm_device_action_run`. It actually helped saving about 700uA, but we still get a baseline of 1mA instead of few uA (that we achieve with the UART disabled in the devicetree). Any pointers? :)

error = pm_device_action_run(DEVICE_DT_GET(DT_NODELABEL(uart1)), PM_DEVICE_ACTION_RESUME);

[Amanda Hsieh]

Hi, 

You can use the power management API as 

// Turn off UART1:

uart1 = device_get_binding(DT_LABEL(DT_NODELABEL(uart1)));

device_set_power_state(uart1, DEVICE_PM_OFF_STATE, NULL, NULL);

See this thread.

Regards,
Amanda

[sixaxix9]

Hi Amanda, thank you for your reply :)

I am getting error -134 when trying to set the UART to state off:

error = pm_device_state_set(DEVICE_DT_GET(DT_NODELABEL(uart1)), PM_DEVICE_STATE_OFF);

Please consider that I am using Zephyr 2.7 (commit in first message) and I have changed the function names accordingly.

[Amanda Hsieh]

Hi, 

sixaxix9 said:

I am getting error -134 when trying to set the UART to state off:

Do you install Zephyr via our NCS? If not, could you install NCS v1.9 which includes Zephyr 2.7? 

sixaxix9 said:

After some digging in the Zephyr power management code I found out that I should be using `pm_device_action_run`. It actually helped saving about 700uA, but we still get a baseline of 1mA instead of few uA (that we achieve with the UART disabled in the devicetree). Any pointers?

Could you also try to set CONFIG_LOG=n and CONFIG_SERIAL=n in the prj.conf?

There is an example provided by my colleague in this thread. Could you also try that?

-Amanda

[sixaxix9]

Hi Amanda, thank you for your answer.

Unfortunately, installing the NCS is not an option, as the code to be used has to be pulled from the Zephyr GitHub repo.

I have LOG functions in the code, so I have to set up CONFIG_LOG always enabled. If I set CONFIG_SERIAL disabled, won't this disable the UART functionality?