nRF9160 Using UART with printf without all the debugging outputs from Zephyr

[JonnyMN]

How do I use printf to output my own messages, and read incoming data, from a UART port that is separate from Zephyr's debugging outputs? This UART line will be connected to another microcontroller for custom commands.

Here is what I have so far:

I want printf messages to be directed to the UART0 port for my program to talk to another device. I also want to be able to read the incoming messages.

Here is my code that works:

while (1) {
		char *s = console_getline();
		printf("Here's your string: %s\n", s);
	}

However, with the above code, I also get what appears to be debug outputs from Zephyr being put on my UART0 line. For example, when the device starts up, I get a bunch of debug messages, etc. Also, any printk() messages are also on UART0.

I thought I could get around this by modifying the kconfig settings (via kconfig or guiconfig). I tried disabling things like the kernal boot banner, logging, etc, but the settings are reset to the defaults after rebuilding the project.

[Øyvind]

Hello, 

You can enable the Logging module of Zephyr by adding #include <logging/log.h> to e.g. main.c and the following lines to prj.conf

# Configure logger
CONFIG_LOG=y
CONFIG_USE_SEGGER_RTT=n
CONFIG_LOG_BACKEND_UART=y
CONFIG_LOG_DEFAULT_LEVEL=4

There are four severity levels available in the system: error, warning, info and debug.

In your main.c add the following lines just before your main loop.

#define LOG_MODULE_NAME app
LOG_MODULE_REGISTER(LOG_MODULE_NAME);

In you application you should be able to replace e.g the printk() with LOG_INF() for debug/logging information.  

This should provide you with the following output

Let me know how that works for you

[JonnyMN]

This did not fix my problem, unfortunately.

Just to clear up any confusion, this is what I'm seeing as the device starts up:

*** Booting Zephyr OS build v2.7.99-ncs1-1  ***
I: Starting bootloader
I: Primary image: magic=bad, swap_type=0x0, copy_done=0x2, image_ok=0x2
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0x10000
I: Jumping to the first image slot
*** Booting Zephyr OS build v2.7.99-ncs1-1  ***
Flash regions..Domain..Permissions
00 03 0x00000 0x20000 .Secure..rwxl
04 31 0x20000 0x100000 .Non-Secure.rwxl

Non-secure callable region 0 placed in flash region 3 with size 32.

SRAM region..Domain..Permissions
00 03 0x00000 0x08000 .Secure..rwxl
04 31 0x08000 0x40000 .Non-Secure.rwxl

Peripheral..Domain..Status
00 NRF_P0               Non-Secure.OK
01 NRF_CLOCK            Non-Secure.OK
02 NRF_RTC0             Non-Secure.OK
03 NRF_RTC1             Non-Secure.OK
04 NRF_NVMC             Non-Secure.OK
05 NRF_UARTE1           Non-Secure.OK
06 NRF_UARTE2           Secure..SKIP
07 NRF_TWIM2            Non-Secure.OK
08 NRF_SPIM3            Non-Secure.OK
09 NRF_TIMER0           Non-Secure.OK
10 NRF_TIMER1           Non-Secure.OK
11 NRF_TIMER2           Non-Secure.OK
12 NRF_SAADC            Non-Secure.OK
13 NRF_PWM0             Non-Secure.OK
14 NRF_PWM1             Non-Secure.OK
15 NRF_PWM2             Non-Secure.OK
16 NRF_PWM3             Non-Secure.OK
17 NRF_WDT              Non-Secure.OK
18 NRF_IPC              Non-Secure.OK
19 NRF_VMC              Non-Secure.OK
20 NRF_FPU              Non-Secure.OK
21 NRF_EGU0             Non-Secure.OK
22 NRF_EGU1             Non-Secure.OK
23 NRF_EGU2             Non-Secure.OK
24 NRF_EGU3             Non-Secure.OK
25 NRF_EGU4             Non-Secure.OK
26 NRF_EGU5             Non-Secure.OK
27 NRF_DPPIC            Non-Secure.OK
28 NRF_REGULATORS       Non-Secure.OK
29 NRF_PDM              Non-Secure.OK
30 NRF_I2S              Non-Secure.OK
31 NRF_GPIOTE1          Non-Secure.OK

SPM: NS image at 0x20200
SPM: NS MSP at 0x20015338
SPM: NS reset vector at 0x25ec1
SPM: prepare to jump to Non-Secure image.
*** Booting Zephyr OS build v2.7.99-ncs1-1  ***

I don't want any of these messages on my UART 0 port. I only want messages that I send using printf() function in my code only. 

Here is what I want to see during device startup:

// nothing, but I had to put something here since the code block wont let me post without any text.

[Øyvind]

Ok, I see. You could use e.g. RTT for logs. See RTT chapter in Logging in nRF Connect SDK. To turn off the "boot banner" you can add CONFIG_BOOT_BANNER=n. 

Also, please see the Zephyr Logging API. 

[JonnyMN]

I added the following to my prj.conf file:

CONFIG_BOOT_BANNER=n

CONFIG_LOG=y
CONFIG_LOG_MODE_MINIMAL=y
CONFIG_LOG_BACKEND_UART=n
CONFIG_USE_SEGGER_RTT=y
CONFIG_LOG_BACKEND_RTT=y

But it had no effect. Boot banner and all the Zephyr start-up messages are still present on UART0.

[JonnyMN]

Are there any updates on this? Again, I want to silence all outputs to the UART0, and only transmit data I send out via a printf() function.

[Øyvind]

My apologies for the late answer. Can you please add the following folder and file to your project folder: child_image/spm.conf

In this file, add the following line: CONFIG_SERIAL=n

Then, in your prj.conf add the following:

CONFIG_UART_CONSOLE=n

CONFIG_RTT_CONSOLE=y 

Let me know how that works for you. 

Kind regards,
Øyvind

[JonnyMN]

I tried your suggestion, but I'm still getting this output from UART0:

*** Booting Zephyr OS build v2.7.99-ncs1-1  ***
I: Starting bootloader
I: Primary image: magic=bad, swap_type=0x0, copy_done=0x2, image_ok=0x2
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0x10000
I: Jumping to the first image slot
+CEREG: 2,"4603","04EE0211",7
+CSCON: 1
+CEREG: 5,"4603","04EE0211",7,,,"11100000","11100000"
%XTIME: "0A","2250011293210A","01"
+CSCON: 0

Would it be easier to use UART1 or UART2 for a custom communication channel instead? Is there any documentation on how to do this? (When I've tried to use UART1 or UART2 be modifying the dts or kconfig files, the program crashes).