Weird Problem where Segger RTT breaks if using more than 8kB of RAM

[edougal]

I started a new software project on the nRF52832 a couple of weeks ago. I've been using Segger RTT for a lot of debugging with no problem throughout the beginning of the process. I've recently hit an issue where the Segger RTT printf statements stop showing up when I use more than 8kB of RAM. I should have almost 49,000 bytes of RAM remaining, so I'm nowhere near close to running out of RAM.

I've gotten to the point where I can compile my code with or without a single global uint32_t variable and if that variable is included the Segger RTT stuff will not work properly (note that as far as I can tell, everything else appears to work properly).

I'm using the S132 Soft Device and am using GCC to compile the code.

Here are the code size results from compilation:

   text	   data	    bss	 
  40860	    176	   7828	

This uses 8004 Bytes of RAM, and that's when the Segger RTT breaks.

Here's the linker script that I'm using:

/* Linker script to configure memory regions. */

SEARCH_DIR(.)
GROUP(-lgcc -lc -lnosys)

MEMORY
{
  FLASH (rx) : ORIGIN = 0x1f000, LENGTH = 0x61000	/* 397312 Bytes */ 
  RAM (rwx) :  ORIGIN = 0x20002128, LENGTH = 0xded8	/* 57048 Bytes */ 
}

SECTIONS
{
  .fs_data :
  {
    PROVIDE(__start_fs_data = .);
    KEEP(*(.fs_data))
    PROVIDE(__stop_fs_data = .);
  } > RAM
} INSERT AFTER .data;

INCLUDE "nrf5x_common.ld"

EDIT: I realized it might be worth mentioning that I'm allocating 4608 Bytes of RAM via the SDK provided memory manager.

[edougal]

That actually worked, but I'm not quite sure why. I'm not printing a lot (just a version number, the BT advertising name, and then some data in a callback. Also, it was commenting or uncommenting other variables (unrelated to the Segger RTT) which caused it to stop working.

Either way it works now, so thank you very much for the suggestion!