nRF SDK pre-built blinky .hex works, compiled .hex does not (nRF51822)

[iforce2d]

I'm using the nRF5 SDK 12.3.0 on Linux (Fedora 33), with a minimal N51822 breakout board (nRF51822-QFAA(build code: H0) 256kB Flash, 16kB RAM).
For programming I'm using a ST-Link v2 and OpenOCD.

Testing with the blinky example, the pre-built .hex file included with the SDK works ok, but the .hex produced by compiling does not.

I'm using version 12.3.0 of the SDK because that seems to be the last one that included pre-built examples for nRF51822.

Here are the steps I took after downloading the SDK.

Modify components/toolchain/gcc/Makefile.posix to specify the compiler:

GNU_INSTALL_ROOT ?= /home/chris/projects/gcc-arm-none-eabi-10.3-2021.07

Go to examples/peripheral/blinky/hex/

Flash the pre-built example .hex to the device like this:

openocd -f interface/stlink.cfg -f target/nrf51.cfg -c "init" -c "halt" -c "nrf51 mass_erase" -c "program blinky_pca10028.hex" -c "reset" -c "exit"

The programming succeeds, and I see the LEDs blinking. I can connect with gdb, pause and resume the execution etc. So everything is fine with the pre-built .hex.

Next I go to examples/peripheral/blinky/pca10028/blank/armgcc/ and run 'make', which compiles successfully:

[chris@localhost armgcc]$ make
mkdir _build
Compiling file: nrf_log_backend_serial.c
Compiling file: nrf_log_frontend.c
Compiling file: app_error.c
Compiling file: app_error_weak.c
Compiling file: app_timer.c
Compiling file: app_util_platform.c
Compiling file: hardfault_implementation.c
Compiling file: nrf_assert.c
Compiling file: sdk_errors.c
Compiling file: boards.c
Compiling file: nrf_drv_clock.c
Compiling file: nrf_drv_common.c
Compiling file: nrf_drv_uart.c
Compiling file: nrf_nvic.c
Compiling file: nrf_soc.c
Compiling file: main.c
Compiling file: RTT_Syscalls_GCC.c
Compiling file: SEGGER_RTT.c
Compiling file: SEGGER_RTT_printf.c
Assembling file: gcc_startup_nrf51.S
Compiling file: system_nrf51.c
Linking target: _build/nrf51422_xxac.out

text data bss dec hex filename
3192 108 112 3412 d54 _build/nrf51422_xxac.out

Preparing: _build/nrf51422_xxac.hex
Preparing: _build/nrf51422_xxac.bin

When I flash the newly compiled .hex using the same method as before, the programming succeeds again. But the LEDs do not blink, and when I connect with gdb the program is always in HardFault_Handler:

[chris@localhost ~]$ telnet localhost 4444
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Open On-Chip Debugger
> halt
target halted due to debug-request, current mode: Handler HardFault
xPSR: 0x61000003 pc: 0x00000b62 msp: 0x20007fe0

Shouldn't the pre-built example be just the same as what we get from compiling? What could be wrong with my toolchain that causes the compiled .hex to fail?

[iforce2d]

ugh.... as usual, after struggling with a problem for two days and then writing up a detailed question, I find the solution myself within minutes of posting my question. It really is unbelievable how this happens every time!

In the file examples/peripheral/blinky/pca10028/blank/armgcc/blinky_gcc_nrf51.ld 

The LENGTH of the RAM section needed to be changed from 0x8000 to 0x4000

MEMORY
{
  FLASH (rx) : ORIGIN = 0x0, LENGTH = 0x40000
  RAM (rwx) :  ORIGIN = 0x20000000, LENGTH = 0x4000
}

I was aware of different RAM sizes in the 51822 variants and I had actually tried this change very early in my struggles, but for some reason it had no effect, probably because I was still screwing up the openocd parameters at the time. So I had changed it back so as to make as few changes as possible to the original. Just tried it again now, and it works - now if only I could get that two days of my life back.