RTT Logging not working when building with ARM GCC

[AntonHellbe]

Hi,

I'm trying to use RTT Logging in my application. If I build and flash my application through Segger Embedded Studio RTT logging works. However If I use ARM GCC to build the application and nrfjprog to flash RTT logging does not work. 

NRF_LOG and BACKEND_RTT is enabled in my sdk_config.h and I'm doing the following calls in main:

APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
NRF_LOG_DEFAULT_BACKENDS_INIT();

For ARM GCC I'm using the generic linker file inside the SDK folder config/nrf52840/generic_gcc_nrf52.ld, with a slight modification to the RAM_START and RAM_SIZE to allow for multiple connections. 

Are there any more modifications that needs to be done in order to enable RTT Logging when using ARM GCC? 

As a side note: UART Backend logging works without any issues when I build with ARM GCC

board: nRF52840 Preview DK

SDK: v15

Softdevice: 6.0.0

Br,
Anton

[Einar Thorsrud]

Hi,

Which version of ARM GCC do you use? We have seen issues with ARM GCC 7.x.x and link time optimization (LTO). (Therefor, the SDK is still tested using version 6.3.1).

[AntonHellbe]

One more thing I forgot to mention in the original post is that before I changed the RAM_START and RAM_SIZE the RTT output worked. However then the application doesn't work since there is not enough memory for the softdevice. 

[Einar Thorsrud]

OK, I see. So probably there is not enough available RAM for the RTT buffer? But then I would have expected you to see a linker error. Does the map file tell you anything useful?

[AntonHellbe]

8132.nrf52840_xxaa.map
I've tried to look through, although I'm not quite sure what do look for. I have uploaded the file in my answer. Perhaps you can see something?

[AntonHellbe]

Here is the part relating to Segger RTT

 .text.SEGGER_RTT_ReadNoLock
                0x0000000000000000      0x100 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_Read
                0x0000000000000000      0x110 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_WriteWithOverwriteNoLock
                0x0000000000000000       0xe8 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_WriteSkipNoLock
                0x0000000000000000       0xa0 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_Write
                0x0000000000000000      0x1f4 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_WriteString
                0x0000000000000000      0x1f8 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_PutCharSkipNoLock
                0x0000000000000000       0x40 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_PutCharSkip
                0x0000000000000000       0xb8 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_PutChar
                0x0000000000000000       0xd4 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_GetKey
                0x0000000000000000      0x104 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_WaitKey
                0x0000000000000000      0x124 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_HasKey
                0x0000000000000000       0x6c _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_HasData
                0x0000000000000000       0x18 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_AllocDownBuffer
                0x0000000000000000       0xc4 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_AllocUpBuffer
                0x0000000000000000       0xcc _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_ConfigUpBuffer
                0x0000000000000000       0xdc _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_ConfigDownBuffer
                0x0000000000000000       0xbc _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_SetNameUpBuffer
                0x0000000000000000       0x98 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_SetNameDownBuffer
                0x0000000000000000       0x98 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_SetFlagsUpBuffer
                0x0000000000000000       0x98 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_SetFlagsDownBuffer
                0x0000000000000000       0x98 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_SetTerminal
                0x0000000000000000      0x160 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .text.SEGGER_RTT_TerminalOut
                0x0000000000000000      0x408 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .bss._ActiveTerminal
                0x0000000000000000        0x1 _build/nrf52840_xxaa/SEGGER_RTT.c.o
 .rodata._aTerminalId
                0x0000000000000000       0x10 _build/nrf52840_xxaa/SEGGER_RTT.c.o

[Einar Thorsrud]

Hi,

I have no explanation at this point, and I do not recall ever seeing this issue earlier. A few additional questions:

• Can you confirm that  you use JLinkRTTViewer.exe to view the logs?
• Does it have any effect if you disable UART logging (so that you only have RTT logging enabled)?
• How have you configured the RTT viewer? It should look similar to this:

 

[AntonHellbe]

Hi,

• Can you confirm that  you use JLinkRTTViewer.exe to view the logs? No, I'm on Linux so I use JLinkExe and JLinkRTTClient to view the logs. When connecting using JLinkExe I use SWD as the interface
• Does it have any effect if you disable UART logging (so that you only have RTT logging enabled)? No, I have disabled UART Logging but still no RTT Logs
• How have you configured the RTT viewer? When using JLinkExe the only option I select is SWD as the interface and then default the rest of selection. This configuration has worked previously.