[NRF52840] Changing Bootloader Size and need to change Linker Script to match

[jspear]

Hello all,

Environment: nRF52840-DK, NRF SDK V15.0.0, SoftDevice s140 v 6.0.0, ARMGCC building with Makefile

I am currently trying to combine the examples of the USB and BLE DFU bootloaders into one bootloader, and I have run into a problem at the linking stage. I have run into this problem multiple times, and more or less would just like some info on this part of the procedure.

I have started by copying the <SDK_ROOT>/examples/dfu/secure_bootloader/pca10056_ble example to another example called <SDK_ROOT>/examples/dfu/secure_bootloader/pca10056_ble_usb, and then added the appropriate source files and include files from the <SDK_ROOT>/examples/dfu/secure_bootloader/pca10056_usb example to the new example. I'm able to compile all the required files but at the linking step I get the following:

Linking target: _build/nrf52840_xxaa_s140.out
/usr/bin/gnu-arm-embedded-toolchain/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld: _build/nrf52840_xxaa_s140.out section `.text' will not fit in region `FLASH'
/usr/bin/gnu-arm-embedded-toolchain/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld: region FLASH overflowed with .data and user data
/usr/bin/gnu-arm-embedded-toolchain/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld: section .bootloader_settings_page VMA [00000000000ff000,00000000000fffff] overlaps section .text VMA [00000000000f8000,000000000010170f]
/usr/bin/gnu-arm-embedded-toolchain/bin/../lib/gcc/arm-none-eabi/8.2.1/../../../../arm-none-eabi/bin/ld: region `FLASH' overflowed by 14260 bytes
collect2: error: ld returned 1 exit status
make: *** [../../../../components/toolchain/gcc/Makefile.common:294: _build/nrf52840_xxaa_s140.out] Error 1

I know I need to make changes to the bootloader flash section in the associated secure_bootloader_gcc_nrf52.ld example linker script, but this is not something I have really done before. I'd like to learn how to go about this as well as get some resources on how to understand and manipulate linker scripts.

I'm sure as I move forward I'll have more issues in regards to the proper building of this combined example, but I really want to get this fundamental understood first.

Thanks!

[jspear]

Realized I had a few extra errors from forgetting to include some settings. I fixed those issues and updated the above output message to reflect the current status (which is now more specific to my question).

[Vidar Berg]

Hello,

The linker output shows that your bootloader has become too big to fit inside bootloader's FLASH area. So, as you indicated, the solution is to allocate more memory to it. You can do so by lowering the FLASH ORIGIN address and increase the LENGTH accordingly. 

As an example, let's say you want to increase the bootloader size by 16K (0x4000 bytes). Then you would have to change the ORIGIN from 0xF8000 to 0xF4000 (0xF8000 - 0x4000) and the LENGTH to 0xA000 (0x6000+0x4000).

+++ b/secure_bootloader_gcc_nrf52.ld
@@ -5,7 +5,7 @@ GROUP(-lgcc -lc -lnosys)
 
 MEMORY
 {
-  FLASH (rx) : ORIGIN = 0xf8000, LENGTH = 0x6000
+  FLASH (rx) : ORIGIN = 0xf4000, LENGTH = 0xA000
   RAM (rwx) :  ORIGIN = 0x20005978, LENGTH = 0x3a688
   uicr_bootloader_start_address (r) : ORIGIN = 0x10001014, LENGTH = 0x4
   bootloader_settings_page (r) : ORIGIN = 0x000FF000, LENGTH = 0x1000

Best regards,

Vidar

[jspear]

Thanks for the response Vidar.

Vidar Berg said:

As an example, let's say you want to increase the bootloader size by 16K (0x4000 bytes). Then you would have to change the ORIGIN from 0xF8000 to 0xF4000 (0xF8000 - 0x4000) and the LENGTH to 0xA000 (0x6000+0x4000).

That seems fairly simple, thanks for the info. In my pursuits of trying to understand the linker scripts, I have stumble across the documentation for it shown here. This has become pretty helpful in my understanding so far, but I was wondering if there are any other resources, either general to the linker scripts, or specific to using linker scripts with Nordic devices. 

Like I mentioned in my original post, I am looking for resources to build my understanding of this topic, so any and all resources would be greatly appreciated!

Joseph

[Vidar Berg]

Hi Joseph,

In most cases you can use the scripts provided in the SDK with little or no modifications. I don't have much for linker scripts except for this post by Memfault which I think gives a good introduction: https://interrupt.memfault.com/blog/how-to-write-linker-scripts-for-firmware. 

[jspear]

Vidar,

Thank you for the link! I'll be sure to read through it to get a good introduction to the concept. I appreciate all your help!

Joseph