RTT logging from application started by bootloader

Question

Hello,
Is it possible to get logs (RTT) from an application started by a bootloader? As of now I don't get anything after the bootloader has jumped to the application start address. 
 If I run the application separately it works. 
 Thanks, Jacob

Hung Bui · Accepted Answer

Hi Jacob, 
 If you have a look here at the section on how RTT work. You can find that it was not the different channel caused the problem, it's the different allocation of RAM area for the RTT Control Block and the RTT buffer location caused the problem. 
 If we match the Control Block address and the RTT buffers location the same on the bootloader and the application, then everything works. 
 This is the modification I did to SEGGER_RTT.c from line 135: 
 static char _acUpBuffer [BUFFER_SIZE_UP] __attribute__((at(0x20003C00)));
static char _acDownBuffer[BUFFER_SIZE_DOWN]__attribute__((at(0x20003F00))); ;
//
// Initialize SEGGER Real-time-Terminal control block (CB)
//
SEGGER_RTT_CB _SEGGER_RTT __attribute__((at(0x20002C00))); 
 
 I used attribute to force the linker to put the buffer is defined location. You don't have to use the same addresses, it can be any where in RAM (of course in the application RAM range).

RTT logging from application started by bootloader

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