RTT Logging not working when building with ARM GCC

Question

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 · Accepted Answer

Hi Anton, 
 Unfortunately, I have not been able to test this again on my side yet due to a busy morning, but I noticed something which I should have spotted earlier. In the printout from JLinkExe I see that you use the configuration for NRF52832_XXAA. So I suspect that what may be happening is that the RTT client is only looking for the RTT buffer within the nRF52832 RAM region, and this only have 64 kB RAM compared to 256 kB in the nRf52840. If the RTT buffer is placed in the upper half this is not found. If this is correct, then it sould be fixed by specifying that you have a nRF52840 device so that the RTT client will look for the RTT buffer in all of the RAM.

RTT Logging not working when building with ARM GCC

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