Main not called

[YYZ]

I'm trying to get a stripped down, simple LED blinking sample to work (like blinky) when building with GCC however main() is never called. I'm guessing I'm either using the wrong startup file or missing a compiler/linker setting? I know the hex file produced from the build process is executable because if I add a call to main() from the bottom of SystemInit() in system_nrf52.c then my code is executed and the LED blinks as expected. If I replace main() with a call to _start() then my code is not executed. So it seems that _start() is not calling main() for some reason? I have not managed to find the right source for crt0.s to see what might prevent _start() from calling main().

I am using SDK 14.2 (although the problem is the same with other versions of the SDK). I am using the 2015 Q3 version of GCC as specified in the SDK release notes. I am using gcc_startup_nrf52.s I am using the linker script blinky_gcc_nrf52.ld (non SD version). I am not building with a soft device. I am not using Keil uVision.

Compiler and linker settings: -DNRF52 -DNRF52832 -DBOARD_PCA10040 -march=armv7e-m -mcpu=cortex-m4 -mthumb -mabi=aapcs -Wall -O0 -I. -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/device -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/boards -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/drivers_nrf/hal -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/drivers_nrf/delay -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/drivers_nrf/nrf_soc_nosd -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/libraries/util -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/toolchain -IC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/toolchain/cmsis/include -LC:/NordicSDK/nRF5_SDK_14.2.0_17b948a/components/toolchain/gcc -Tblinky_gcc_nrf52.ld

Any ideas as to what I am missing?

Thanks!

[YYZ]

I've worked around this by adding the following compiler/linker options to bypass _start and instead call my main():

-nostartfiles -D__START=main -D__STARTUP_CLEAR_BSS

This bypasses _start provided by crt0 - I do not know if this will cause problems later on though.

[Bjørn Kvaale]

So did you find the solution to your problem then? Did you know that segger embedded studio (ses) is free for Nordic SDK users? The Blinky example is available in SDK 14.2 under the ble_peripheral folder/ble_app_blinky. Then, just choose your dev kit folder, choose the softdevice folder & open the ses folder. There, you can open the ses file (e.g. examples/ble_peripheral/ble_app_blinky/pca10040/s132/ses/ble_app_blinky_pca10040_s132). If you do decide to use ses, there is a great introductory playlist to getting started with ses on Nordic's Youtube channel.

[YYZ]

Only by using the workaround I posted as a comment and I've yet to prove if that is still valid for a more complex example that includes a soft device. It appears that the tools that work out of the box have a modified toolchain and/or include a custom version of crt0.s. I'm curious though how this works with GCC 4.9.3 which is supposed to be supported according to the SDK release notes?

[Vidar Berg]

Hi, recommend that you copy the linker and compiler flags from our example. We use the pre-compiled crt0 library in our examples (included in toolchain release - developer.arm.com/.../downloads).

[YYZ]

Thanks for the suggestion. It turns out the problem was the IDE I am using (EmBitz) silently adding a couple library paths to the link line causing the linker to pick up one wrong startup file. Now my app starts up as expected and calls main without me having to supply any hacks.

Thanks for your help.