topic K22: Hard Fault (exception #3) after floating point instruction in Kinetis Microcontrollers

K22: Hard Fault (exception #3) after floating point instruction

thomas_k1 — Mon, 02 Nov 2020 13:52:57 GMT

I do have a project based on ProcessorExpert where I now start with some calculation.

I'm using

MK22FX512VMC12
ProcessorExpert 10.4.0 b140319
winIDEA 9.12.157
GCC arm-2013q3
No RTOS

Up to now everything worked fine so far. Now I'm trying to scale some measurement values and with the first math instruction I enter hardware fault exception (vector #3).

I guess that I doing something wrong in software but I don't know what.

My settings may be wrong - but floating point settings seems to be OK.

Compiler:

-c $(EDNAME) -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard 
-gdwarf-2  -Wall -ffast-math -fomit-frame-pointer 
-I$(IRFDIR)\Generated_Code -I$(IRFDIR)\Sources 
-I"%PROCESSOR_EXPERT_PATH%\lib\Kinetis\iofiles" 
-I"%PROCESSOR_EXPERT_PATH%\lib\Kinetis\pdd\inc" 
-D__GNU__ -D__PE__‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Linker:

-mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=hard 
-Wl,-T,$(INDPATH) -Wl,-Map,$(OUTPUTDIR)\kernel.map,
--gc-sections -o $(OUTPUTPATH)‍‍‍‍‍‍‍‍‍

I do not understand why an instruction

vldr.32 s14,[r3]‍‍‍

causes the hardware fault excpetion. The CPU has an FPU, so it should work.

It would be great if anybody can help me with that.

Do I have to ENABLE the FPU? (If so where do I find it in PE?)
Is there an error in the command line of compiler or linker?

Thank you very much

Thomas

Re: K22: Hard Fault (exception #3) after floating point instruction

mjbcswitzerland — Mon, 27 Mar 2017 19:24:36 GMT

Hi Thomas

CPACR |= (0xf << 20); // enable access to FPU

Regards

Mark

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Re: K22: Hard Fault (exception #3) after floating point instruction

thomas_k1 — Tue, 28 Mar 2017 07:29:31 GMT

Hello Mark,

thanks a lot you for your hint - it solved my problem.

If someone has the same problem and is reading this thread and now searching for CPACR register: I neither find in in my headers nor is it documented in the Kinetis K22 Sub-Family Reference Manual. Use "CPACR" to find other threads which provide an assembler snippet to enable FPU access

Thanks again to Mark!

Regards

Thomas

Re: K22: Hard Fault (exception #3) after floating point instruction

mjbcswitzerland — Tue, 28 Mar 2017 12:12:38 GMT

Thomas

The Cortex-M4 core is not described in the user's manual because it is a 'standard' part from ARM. That means that anything to do with the core is fully documented by ARM at their "ARM Information Center". For enabling floating point see http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0439b/BEHBJHIG.html

Regards

Mark

P.S. Since the register is memory mapped it doesn't need any special instructions to access it so I would avoid assembler code (to ensure portability). If your framework doesn't supply it just add

#define CORTEX_M4_BLOCK 0xe000e000
#define CPACR *(unsigned long *)(CORTEX_M4_BLOCK + 0xd88) // Co-processor Access Control Register

Re: K22: Hard Fault (exception #3) after floating point instruction

egoodii — Tue, 28 Mar 2017 15:39:22 GMT

FYI, the MK22FA header file I access calls that SCB_CPACR, as part of the whole System-Control-Block at 0xE000E000

Re: K22: Hard Fault (exception #3) after floating point instruction

thomas_k1 — Thu, 30 Mar 2017 07:56:50 GMT

Hi Mark, Earl,

thanks for your answers.

I now find the SCB_CPACR block and can use it to setup FPU in C.

As beginner with ARM it was a good lessen to learn about standard parts and ARM information center :-)

regards

Thomas