How to redirect printf to UART when using Segger Embedded Studio

[northernLight]

The Segger Compiler is integrated with JLINK debugging software

Printf statements, when compiled, direct to the studio debugger terminal

How can I create code where they are directed to the UART?

Project options allow configuration of printf and scanf format but not its output

I am using the uart example in Nordic SDK 12.3. The only way so far that I have found to 'print' to the UART is using a custom print function:

void uart_printf(const char *fmt, ...)
{
char buf[200], *p;
va_list ap;
va_start(ap, fmt);
vsnprintf(buf, sizeof(buf), fmt, ap);
for (p = buf; *p; ++p)
app_uart_put(*p);
va_end(ap);
}

This works but seems laborious;  what is the elegant way?

Many thanks

Rob

[AndreasF]

Hi Rob.

The startup files are code which are run before main starts, you can call it a bootstrapping of the system, so you are correct in that they are "in effect the boot file".

northernLight said:

As a recap of the problem I am trying to solve:  I would like to redirect printf (or stop its current redirection) so that the compiled code operates without Segger Studio, just with a UART connection

Does stdio.h define the standard output destination for putchar()?

 I don't think you should have to add anything to the code, you should only need the correct configuration in sdk_config.h and include the file retarget.c.

Can you try with my configuration: sdk_config.h

I think the vital thing is that you have defined this as 1:

// <e> NRF_LOG_BACKEND_SERIAL_USES_UART - If enabled data is printed over UART
//==========================================================
#ifndef NRF_LOG_BACKEND_SERIAL_USES_UART
#define NRF_LOG_BACKEND_SERIAL_USES_UART 1
#endif

And this as 0:

// <e> NRF_LOG_BACKEND_SERIAL_USES_RTT - If enabled data is printed using RTT
//==========================================================
#ifndef NRF_LOG_BACKEND_SERIAL_USES_RTT
#define NRF_LOG_BACKEND_SERIAL_USES_RTT 0
#endif

As you can see here from the configuration wizard:

Hope this works for you.

Best regards,

Andreas

[northernLight]

Andreas

Thankyou for your time on this.

I believe these only configure NRF_LOG instructions, not direct printf commands

When using NRF_LOG_INFO commands with RTT set and UART unset I get data to the debug terminal in SES

But with the same code with RTT unset and UART set I get no output to my serial monitor window

:-(

What is the function of retarget.c?  Does it affect the destination for standard output?

I am using the sdk_config for the peripheral/uart example from SDK 12.3.  I'll try the file you propose.

How do I incorporate flash_placement.xml in the compiler configuration?

Many thanks

Rob

 

[AndreasF]

Hi.

northernLight said:

Thankyou for your time on this.

I believe these only configure NRF_LOG instructions, not direct printf commands

When using NRF_LOG_INFO commands with RTT set and UART unset I get data to the debug terminal in SES

But with the same code with RTT unset and UART set I get no output to my serial monitor window

This is not what happend with the sdk_config.h file I gave you?

northernLight said:

What is the function of retarget.c?  Does it affect the destination for standard output?

 It is an implementation of functions in stdio.h.

northernLight said:

How do I incorporate flash_placement.xml in the compiler configuration?

 Follow step 7 on this guide.

Best regards,

Andreas