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.

[Einar Thorsrud]

Hi,

JLinkExe and JLinkRTTClient should work out of the box and you got it working previously, so this should not be related then. This is puzzling, and have asked around the office, but one of those I talked to had seen this behaviour earlier. Do you get any errors or other interesting logs from JLinkExe or JLinkRTTClient?