RTT logging: no output in SDK 11?

[Eliot Stock]

Hi there,

I'm in the middle of migrating an application from SDK 10 to SDK 11. In the SDK 10 version, I had RTT logging working just fine. I'm developing on a Mac so I had to start Segger's GDB server in order to get the RTT client to run. I have three terminal tabs open. A .gdbinit file exists for these. I run these in this order:

1. GDB server:

   /Applications/SEGGER/JLink/JLinkGDBServer -device nrf51822 -if swd -speed 4000 -port 2331

2. GDB Client:

   /Users/Eliot/dev/gcc-arm-none-eabi-4_9-2015q1/bin/arm-none-eabi-gdb -x _build/.gdbinit _build//*.elf

3. RTT Client:

   /Applications/SEGGER/JLink/JLinkRTTClient

I then need to "cont" and "cont" again in the GDB client to start my code. In SDK 10, I saw output on the RTT client terminal tab. In SDK 11, no such luck.

I retarget printf() in my code. syscalls.c looks like this:

int _write(int file, char *ptr, int len)
{
	UNUSED_PARAMETER(file);
	uint32_t bytes_written = 0;

#ifdef BIKE_TRACKER_TEST
	SEGGER_RTT_Write(0, ptr, len);
#else

	if (ble_connected())
	{
		write_over_ble(file, ptr, len);
	}
	else
	{
		bytes_written = SEGGER_RTT_Write(0, ptr, len);
		UNUSED_PARAMETER(bytes_written);
	}
#endif

	return len;
}

The Segger RTT stuff is definitely getting compiled and linked in in my build:

APPLICATION_SRCS += SEGGER_RTT.c
APPLICATION_SRCS += SEGGER_RTT_printf.c
...
SOURCE_PATHS += $(SDK_PATH)../external/segger_rtt

I've read the tutorial here: devzone.nordicsemi.com/.../

I've debugged the code and set a breakpoint in SEGGER_RTT.c at the start of SEGGER_RTT_Write(). That function is executing. SEGGER_RTT_WriteNoLock() is returning 7, which is about the number of characters I was writing when I debugged it.

Neither a straight printf() nor a call to NRF_LOG() is producing anything on the RTT client. It just sits there saying:

Process: 

I'm running V5.12f of the Segger stuff, the latest at the time of writing.

[Vidar Berg]

Hi,

Please try with a clean copy of one of the standard BLE examples from the SDK and add the LOG macros in the main loop:

int main()
{
     // Initialize.
     NRF_LOG_INIT();
     ....

     // Start execution.
     ...... 

// Enter main loop.
for (;;)
{
    NRF_LOG("print something");
} 

And make sure to add -DNRF_LOG_USES_RTT=1 compiler flags before building. This worked on my OSX setup using J-link V.5.12f. If it does work you could just copy the implementation into your project.

[Aaron]

I am also having trouble with RTT porting an existing app to v11. In my case it seems I'm running into the "In some cases J-Link cannot locate the RTT buffer in the known RAM region." issue from www.segger.com/jlink-rtt.html. I ran

exec SetRTTAddr 20002c40

from JLinkExe, where 20002c40 was the location of _SEGGER_RTT in the _build/nrf51822_xxaa_s130.map file, and RTT started working. The FAQ linked says that

eval "monitor exec SetRTTAddr %p", &_SEGGER_RTT

should work from gdb but I haven't tried it. Trying to get RTT working so that I can avoid gdb in the first place.

[Eliot Stock]

Thank you so much! This has been killing me.

[Eliot Stock]

Coming back to my own question ages later, another thing that caught me out was that the default logging level in the sdk_config.h I was using was 3 (info) and I had been testing logging with NRF_LOG_DEBUG() (level 4). Maybe this'll help someone else in the same situation.