RTT logging from application started by bootloader

RE: RTT logging from application started by bootloader

Hung Bui — Tue, 06 Jan 2026 08:49:39 GMT

Khalid Syed This is a very old ticket, please create a new ticket for your question

RE: RTT logging from application started by bootloader

Khalid Syed — Thu, 01 Jan 2026 22:55:12 GMT

Where can I find SEGGER_RTT.c and the .Id files?

RE: RTT logging from application started by bootloader

Benjamin — Thu, 29 Apr 2021 18:30:35 GMT

I also have these macros defined, with the above RTT macros, but I don't remember exactly why:

#define SEGGER_RTT_CONFIG_BUFFER_SIZE_UP 4096
#define SEGGER_RTT_CONFIG_MAX_NUM_UP_BUFFERS 2
#define SEGGER_RTT_CONFIG_BUFFER_SIZE_DOWN 16
#define SEGGER_RTT_CONFIG_MAX_NUM_DOWN_BUFFERS 2
#define SEGGER_RTT_ALIGNMENT 4
#define SEGGER_RTT_BUFFER_ALIGNMENT 4
#define SEGGER_RTT_SECTION ".rtt_cb"
#define SEGGER_RTT_BUFFER_SECTION ".rtt_buffers"

I also added NOLOAD directives to my linker script (again, don't remember exactly why):

.rtt_buffers(NOLOAD) :

.rtt_cb(NOLOAD) :

Let me know if one of those works and I'll update my previous post.

RE: RTT logging from application started by bootloader

swisst — Thu, 29 Apr 2021 10:00:17 GMT

Thanks for quick reply but no result for now

BTW SDK v17.0.2, JLink toolset 6.88

RE: RTT logging from application started by bootloader

Benjamin — Wed, 28 Apr 2021 14:41:37 GMT

I discovered a couple of things:

The RTT control block must be zeroed out before RTT's init is called (it doesn't zero it's special memory block, but the RTT tools expect it to be zeroed aside from its special bytes).

Sometimes the RTT tools can take a while to find the memory block, but you can create a jlink script to help them:

/* set_RTT_location.jlinkscript */
/* Command-line options: -nogui -select USB -device nRF52840_xxAA -if SWD -endian little -speed 4000 -jlinkscriptfile path/to/set_RTT_location.jlinkscript */
/* Alternatively, run command from gdb CLI: eval "monitor exec SetRTTAddr %p", &_SEGGER_RTT */
int SetupTarget(void) {
    JLINK_ExecCommand("SetRTTAddr 0x2003EF78");
}

RE: RTT logging from application started by bootloader

swisst — Wed, 28 Apr 2021 13:00:56 GMT

I've implemented implemented in such way but my RTT does not starts

As I see differences from original implementation - a load address is not specified for both sections ( top part )

- top part is original rtt location

- bottom part is custom rtt location

.igot.plt       0x00000000200051f4        0x0 load address 0x0000000000041528
 .igot.plt      0x00000000200051f4        0x0 toolchain/gcc-arm-none-eabi-10-2020-q4-major/bin/../lib/gcc/arm-none-eabi/10.2.1/thumb/v7e-m+fp/hard/crtbegin.o

.rtt_buffers    0x00000000200051f4      0x210 load address 0x0000000000041528
 .rtt_buffers   0x00000000200051f4      0x210 /tmp/nrf52840_xxaa.out.22h15i.ltrans0.ltrans.o

.rtt_control_block
                0x0000000020005404       0x78 load address 0x0000000000041738
 .rtt_control_block
                0x0000000020005404       0x78 /tmp/nrf52840_xxaa.out.22h15i.ltrans0.ltrans.o
                0x000000002000547c                . = ALIGN (0x4)


.igot.plt       0x00000000200051f4        0x0 load address 0x0000000000041528
 .igot.plt      0x00000000200051f4        0x0 toolchain/gcc-arm-none-eabi-10-2020-q4-major/bin/../lib/gcc/arm-none-eabi/10.2.1/thumb/v7e-m+fp/hard/crtbegin.o

.rtt_buffers    0x000000002003fd78      0x210
 *(.rtt_buffers)
 .rtt_buffers   0x000000002003fd78      0x210 /tmp/nrf52840_xxaa.out.SzFaPv.ltrans0.ltrans.o

.rtt_control_block
                0x000000002003ff88       0x78
 *(.rtt_control_block)
 .rtt_control_block
                0x000000002003ff88       0x78 /tmp/nrf52840_xxaa.out.SzFaPv.ltrans0.ltrans.o
                0x0000000020040000                . = ALIGN (0x4)

please advise

RE: RTT logging from application started by bootloader

Benjamin — Fri, 16 Oct 2020 03:55:41 GMT

For anyone encountering this problem now, since at least SDK 16 (haven't looked back further), you can simply define a few macros in your app/sdk_config.h:

#define SEGGER_RTT_ALIGNMENT 4
#define SEGGER_RTT_BUFFER_ALIGNMENT 4
#define SEGGER_RTT_SECTION ".rtt_cb"
#define SEGGER_RTT_BUFFER_SECTION ".rtt_buffers"

and add the corresponding sections to your linker files:

MEMORY
{
  ...
  /* Put RTT data at top of RAM. */
  /* RTT_CB LENGTH = 24 + SEGGER_RTT_CONFIG_MAX_NUM_UP_BUFFERS * 24
                        + SEGGER_RTT_CONFIG_MAX_NUM_DOWN_BUFFERS * 24 */
  RTT_CB (rw) : ORIGIN = 0x2003ff88, LENGTH = 0x78
  /* RTT_BUFFERS LENGTH = + SEGGER_RTT_CONFIG_BUFFER_SIZE_UP
                          + SEGGER_RTT_CONFIG_BUFFER_SIZE_DOWN */
  /* RTT_BUFFERS ORIGIN = 0x20040000 - CB LENGTH - BUFFERS LENGTH */
  RTT_BUFFERS (rw) : ORIGIN = 0x2003ef78, LENGTH = 0x1010
}

SECTIONS
{
  .rtt_buffers :
  {
    KEEP(*(.rtt_buffers))
  } > RTT_BUFFERS
  .rtt_cb :
  {
    KEEP(*(.rtt_cb))
  } > RTT_CB
}

RE: RTT logging from application started by bootloader

Hung Bui — Mon, 05 Mar 2018 10:48:23 GMT

Please state what exactly you did to assign the address of the segger rtt buffer. I would suggest you to create a new case with the link to this case.

RE: RTT logging from application started by bootloader

schef — Fri, 02 Mar 2018 12:47:59 GMT

Ok here is what i have found in `sdk_config.h`:

`#define SEGGER_RTT_CONFIG_BUFFER_SIZE_UP 1024`
`#define SEGGER_RTT_CONFIG_BUFFER_SIZE_DOWN 16`

which is used for `BUFFER_SIZE_UP` and `BUFFER_SIZE_DOWN`.

so if start location is `0x20006000` then:

```

>>> hex(int('20006000', 16) + 1024)
'0x20006400'
>>> hex(int('20006000', 16) + 1024 + 16)
'0x20006410'

```

would be the next two.

But then i get the error:

`/home/work/software/arm/gcc-arm-none-eabi-4_9-2015q3/bin/../lib/gcc/arm-none-eabi/4.9.3/../../../../arm-none-eabi/bin/ld: section .rtt_ac_down loaded at [20006400,2000640f] overlaps section .rtt_ac_up loaded at [20006000,20006fff]`

The i have moved to:

`0x20006000`, `0x20007000`, `0x20007010`.

It compiles but the issue is not fixed. I still have to use connect in jlinkexe to see the application code.

RE: RTT logging from application started by bootloader

schef — Fri, 02 Mar 2018 12:09:43 GMT

What is recomended place for RAM and what are the sizes needed?

RE: RTT logging from application started by bootloader

Jacob — Thu, 30 Mar 2017 08:06:07 GMT

Cool - got it working now with GCC like this:

static char __attribute__((section(".rtt_ac_up"))) _acUpBuffer  [BUFFER_SIZE_UP];
static char __attribute__((section(".rtt_ac_down"))) _acDownBuffer[BUFFER_SIZE_DOWN];
SEGGER_RTT_CB __attribute__((section(".rtt_segger"))) _SEGGER_RTT;

and corresponding .ld file:

SECTIONS
{
  .rtt_ac_up 0x20003000 :
  {
    KEEP(*(.rtt_ac_up))
  } > RAM
  .rtt_ac_down 0x20003800 :
  {
    KEEP(*(.rtt_ac_down))
  } > RAM
  .rtt_segger 0x20003880 :
  {
    KEEP(*(.rtt_segger))
  } > RAM
}

Thank you so much for the help!

RE: RTT logging from application started by bootloader

Hung Bui — Tue, 28 Mar 2017 11:42:58 GMT

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).

RE: RTT logging from application started by bootloader

Jacob — Mon, 27 Mar 2017 12:43:32 GMT

Hello, When developing boot issues it is very helpful to get output from both the bootloader and the application. Can I get the output from the second RTT channel then?

Thanks, Jacob

RE: RTT logging from application started by bootloader

Hung Bui — Thu, 23 Mar 2017 16:55:46 GMT

Hi Jacob,

When I tested here (SDKv13), it seems that when we reinit the log module we will actually open another RTT channel.

So if I open RTT client when the application running, I can only capture the RTT log from the application, even if I reset the device and the device enter the bootloader before it get to the application.

If I open RTT client when the bootloader is running and enterred bootloader mode, then I can follow the RTT client of the bootloader.

Do you really need RTT to be ON on the bootloader ? If you turn it off can you get RTT log on the application ?

RE: RTT logging from application started by bootloader

Jacob — Thu, 23 Mar 2017 10:28:14 GMT

RTT logging from the bootloader works (and is apparently turned on). RTT logging from the application works if I run it standalone, but if I start it from the bootloader I don't get any output.

Will try SEGGER_RTT_Init(). Thanks.

RE: RTT logging from application started by bootloader

Hung Bui — Thu, 23 Mar 2017 10:26:30 GMT

Did you also turn on RTT logging in the bootloader ?

RE: RTT logging from application started by bootloader

butch — Wed, 22 Mar 2017 15:21:29 GMT

Can you provide more information about what you tried? Did you call SEGGER_RTT_Init() in your code and did you start the GDB server and the JLinkClient? I don't have any experience with boot loaded code, just with RTT using the debugger to load code.