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

[northernLight]

Hi Andreas

Thanks for the prompt.  I followed the tutorial importing the Keil project from examples/periperals/UART/blank - target NRF51822 QFAA

However I do not remember modifying the internal files after the import.  Which ones should I use for this SoC?

The tutorial is based upon the 52 series

BW

Rob

[AndreasF]

Hi.

Can you use the files system_nrf51.c and system_nrf51.h found in \components\toolchain

Download this zip file:embedded_studio.zip

And place it like I have on my picture, in \components\toolchain

Inside this file is a flash_placement.xml, ses_nrf51_startup.s and thumb_crt0.s which should work.

Best regards,

Andreas

[northernLight]

Andreas,

Many thanks. I am unsure what to do with the flash_placement.xml.

I included the *.s files in the build and excluded the old ones:

But I get the following build errors:

Building ‘twi_master_using_app_twi_pca10028_sdk12’ from solution ‘twi_master_using_app_twi_pca10028_sdk12’ in configuration ‘nrf51422_xxac’
1> Assembling ‘ses_nrf51_startup.s’
2> Assembling ‘thumb_crt0.s’
1> Linking twi_master_using_app_twi_pca10028_sdk12.elf
1>
1> Diagnostics:
1> remark: increasing alignment of section .vectors from 1 to 2 because it contains executable instructions
1> error: undefined symbol: __SEGGER_init_copy
1> error: undefined symbol: __SEGGER_init_zero
1> error: undefined symbol: __SRAM_segment_end__
1> error: undefined symbol: __bss_end__
1> error: undefined symbol: __bss_start__
1> error: undefined symbol: __ctors_load_start__
1> error: undefined symbol: __data_end__
1> error: undefined symbol: __data_load_start__
1> error: undefined symbol: __data_start__
1> error: undefined symbol: __dtors_load_start__
1> error: undefined symbol: __fast_end__
1> error: undefined symbol: __fast_load_start__
1> error: undefined symbol: __fast_start__
1> error: undefined symbol: __rodata_end__
1> error: undefined symbol: __rodata_load_start__
1> error: undefined symbol: __rodata_start__
1> error: undefined symbol: __stack_process_end__
1> error: undefined symbol: __stack_process_start__
1> error: undefined symbol: __text_end__
1> error: undefined symbol: __text_load_start__
1> error: undefined symbol: __text_start__
Build failed

It seems I should keep the Segger_thumb?

But then I get errors:

Building ‘twi_master_using_app_twi_pca10028_sdk12’ from solution ‘twi_master_using_app_twi_pca10028_sdk12’ in configuration ‘nrf51422_xxac’
2> Assembling ‘SEGGER_THUMB_Startup.s’
1> Linking twi_master_using_app_twi_pca10028_sdk12.elf
1>
1> Diagnostics:
1> error: multiply defined global symbol _start
1> error: defined by thumb_crt0.o
1> error: and by SEGGER_THUMB_Startup.o
1> remark: increasing alignment of section .vectors from 1 to 2 because it contains executable instructions
1> error: undefined symbol: __SRAM_segment_end__
Build failed

Rob

[northernLight]

As a check I reverted to the original files and the build completed

Thanks again for helping with this. 

For my education what is the broad purpose of these start-up files?  They seem to be the first instructions that the processor executes on power-up. 

Are they in effect the boot file?

Rob

[northernLight]

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()?

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