how to disable UART0 for low power

[Timothy]

I have a custom nRF9160 board running a modified asset_tracker program. I am using UART0 as a command line interface for testing and debugging. I can enter commands to setup and test the hardware. All is working perfectly. When the nRF9160 board is deployed in the field I need to run on batteries and no longer need the command line interface. Is there a simple or preferred way to disable the UART0 in order to reduce the power without making a completely new code base. The lower power is critical to the application.

[Hung Bui]

Hei Timothy, 
You should be able to turn off UART by 
CONFIG_SERIAL=n
You may turn off CONSOLE as well, just in case it's enabled somewhere: 
CONFIG_CONSOLE=n
CONFIG_UART_CONSOLE=n
CONFIG_STDOUT_CONSOLE=n
CONFIG_PRINTK=n
CONFIG_EARLY_CONSOLE=n

If you have MCUBoot enabled, you would need to turn off UART log for MCUBoot as well.  You can add CONFIG_SERIAL=n into mcuboot.conf file in child_image folder. 

[Timothy]

Hung

thank you for your quick response. I changed the "CONFIG_SERIAL=y" to "CONFIG_SERIAL=N" and was not able to build. I got the following errors. what else am I missing? 

[Timothy]

Hung

I tried to use the second method in the example you gave but I get.

fatal error: power_manager.h: No such file or directory

the example is 2 years old. so how do I disable the power dynamically in V2.5.0

the Serial.c file uses UART2. it has nothing to do with UART0.

I have attached the jfet_init.c.

jfet_init.c

[Hung Bui]

Hi Timothy, 

I didn't know that you use multiple UARTs in your code. When setting CONFIG_SERIAL=n all UARTs will be disabled so if you want to only disable UART0 when enable UART1 you will have to do approach #2. 

From what I can see in your jfet_init.c code you did use UART0: 

const struct device *const uart0_dev = DEVICE_DT_GET(UART0_DEV_NODE);

You may want to consider remove those code. 

And if you use UART1 actively don't think you can reduce a lot of power by disabling UART0. 

[Timothy]

Hung

I was able to disable UART0 dynamically using method 2 with no change in the code. I will test this for power levels and disable UART2 also if needed at the customer site.

[Timothy]

Hung

I was able to disable UART0 dynamically using method 2 with no change in the code. I will test this for power levels and disable UART2 also if needed at the customer site.

[Timothy]

I have upgraded to V2.5.0 and I am trying to disable UART 0 using the following

    pm_device_action_run(uart0_dev, PM_DEVICE_ACTION_SUSPEND);

or

    pm_device_state_set(uart0_dev, PM_DEVICE_STATE_OFF);

in either case I get the message "undefined reference to xxx". I have 

"#include <zephyr/pm/device.h>"

what am I doing wrong. How do I disable UART0? This is an urgent problem for production to reduce power.