nRF52 hard fault when running sd_softdevice_enable

RE: nRF52 hard fault when running sd_softdevice_enable

RK — Mon, 13 Jul 2015 11:30:23 GMT

I asked a separate question about this here devzone.nordicsemi.com/.../

The use of the FPU in the SD 132 is unintentional and the requirement should eventually disappear, which is good news.

RE: nRF52 hard fault when running sd_softdevice_enable

TimW — Sat, 11 Jul 2015 05:59:21 GMT

After more experimenting I found this combination to compile, enable the FPU and not crash in the startup code:

-mfloat-abi=softfp -mfpu=fpv4-sp-d16

I have some assembly code which, though it doesn't use floating point, didn't like the hard float option.

RE: nRF52 hard fault when running sd_softdevice_enable

RK — Sat, 11 Jul 2015 05:34:24 GMT

Hmm - something a bit smelly here - I agree the softdevice shouldn't need FP support .. unless it's using some of the vector functions - an answer from Nordic here would help.

-mfloat-abi=soft

can't be right, I think you need

-mfloat-abi=hard -mfpu=fpv4-sp-d16

both of those. My guess would be your crash in _start was the compiler compiling some something for the wrong fp unit. Those flags should hopefully trigger the _start code to turn the FPU unit on too.

RE: nRF52 hard fault when running sd_softdevice_enable

TimW — Sat, 11 Jul 2015 05:23:31 GMT

You're correct; the FPU does need to be enabled. I hadn't bothered because I couldn't imagine the softdevice would be using it and my code doesn't either. I didn't realize it was disabled by default to save power. I had to force-enable it however. I tried using the -mfloat-abi=softfp option which appears to enable the system_nrf52.c code, but then my code crashed somewhere in _start. Just forcing the FPU on by hand worked though (not a great long term solution).

RE: nRF52 hard fault when running sd_softdevice_enable

RK — Sat, 11 Jul 2015 01:14:25 GMT

Is the FPU enabled? It's a while since I read the FPU unit documentation but I remember most instructions cause a fault if the FPU isn't. There's code to enable it in system_nrf52.c

I am however a little surprised the FPU is used in the softdevice since it's not required to be enabled and, apart from just generically setting things up to a known state, I can't see why the softdevice would use it.

Do you have an address of that instruction, any other addresses in the stack would be handy too, I was going to take a look at the assembler see what's going on.

I wish I had more time to play with my 52 devkit .. sigh.