[Dprglist] gcc ARM Cross Compiler help

[Steve Edwards]

i mean I use VisualGDB, I also use WinDBG, but that is a debugger. :)

On Thu, Dec 22, 2016 at 7:45 PM, Steve Edwards <steve.edwards214 at gmail.com>
wrote:

> I am not a compiler expert nor have I ever used *arm-none-eabi-gcc cross
> compiler under linux* but i have WinDBG under Windows that cross compiles
> with  \sysgcc\arm-eabi 6.2.0.
>
> This may help.  i created two projects, both target same board
> STM32F401RE, one enables HW FPU support and one uses Software FPU. you can
> compare the makefiles to see several differences.  perhaps it will give you
> the info you need.
>
> -hth Steve
>
> On Thu, Dec 22, 2016 at 5:16 PM, David Anderson <davida at smu.edu> wrote:
>
>> For any who have worked with the STMicros STM32401RE board using the
>> arm-none-eabi-gcc cross compiler under linux.  The LMX RTOS code is now
>> running on the board and I can flash leds and write output to a UART.
>>
>> But there is a problem with the math generated by the compiler. Basically
>> the math function "divide"  (/)  for single precision integers works, but
>> crashes for double precision and for floats, doubles etc.
>>
>> Suspicious that it was something I'm doing, I stripped out everything,
>> told the loader to give it a lot of stack space,  wrote this simple test,
>> and turned off the -O2 optimizer:
>>
>> #include "main.h"
>> #include "leds.h"
>>
>> /* ------------------------------------------------------------
>> ----------------*/
>> /* main */
>> /* ------------------------------------------------------------
>> ----------------*/
>>
>> int a,b,c;
>> // long a,b,c;
>> // long long a,b,c;
>> // float  a,b,c;
>> // double a,b,c;
>>
>> int main(void)
>> {
>>         /* initialize */
>>         leds_init();
>>         LED2_ON;
>>
>>         a = 65535;
>>         b = 10;
>>         c = a / b;
>>
>>         LED3_ON;
>>         while (1) {};
>>
>>         /* should never get here */
>>         return 0;
>> }
>>
>> /* ------------------------------------------------------------ */
>>
>> The code turns on one LED, runs the math test, and turns on the second
>> LED.   This works with ints and longs, but fails (2nd LED never lights)
>> with long longs and floats and doubles.  I added casts for the appropriate
>> constants but it didn't make any difference.
>>
>> I dumped the assembly code to see what was generated, and it appears that
>> the ints and longs are divided by the machine instruction "sdiv" while the
>> long longs call the function "__aeabi_ldivmod" and the floats call the
>> function "__aeabi_fdiv".  But neither one of those calls appear to work.
>>
>> And why is it calling a function?  I thought this ARM Cortex-M4 processor
>> included a hardware single precision FPU (FPv4-SP)?   Did I leave out some
>> flag when building the compiler, newlib, or the application?  I think they
>> were all built with "-mcpu=cortex-m4". Is something else required?  I tried
>> "-mfpu=fpv4-sp" but the compiler said "no such thing" and offered
>> fpv4-sp-d16 as the closest option.  It did not help.
>>
>> So... help!  Anyone seem this before?  Any of you compiler guru's have
>> any suggestions?
>>
>> much thanks,
>> dpa
>>
>>
>>
>>
>>
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>
>
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