Looking for a trig function library?

[abarnett]

Posted on March 02, 2017 at 21:27

I am using an STM32F407 (new to ST and this processor) and I need to be able to calculate sines, cosines, square roots, various other trig functions for a power conversion application.  

Is there a math library I can download that contains these functions? 

Thanks in advance for any assistance.

[Danish1]

Posted on March 02, 2017 at 21:35

If you're using a C compiler (or pretty much any high-level language) then it should have trig functions built-in.

With C or C++ you'd have to #include <math.h>.

With 8-bit processors such as PIC16, I would often drop to assembly code. But for the size of project that would justify stm32, I find the benefits of C / C++ greatly outweigh the minor loss in ultimate achievable performance.

Hope this helps,

Danish

[Tesla DeLorean]

Posted on March 02, 2017 at 21:47

#include <math.h> ??

32-bit float variant, though FPU doesn't support transcendental functions natively

cosf(), sinf(), sqrtf(), powf()

[abarnett]

Posted on March 02, 2017 at 21:48

Danish Ali, thanks for the prompt response.  I've tried the math.h funciton and it takes too long (30us) to execute.  Not sure if I'm doing something wrong here.  

I guess I'm looking for something from a motor drive library, maybe something used for Park / Clark transformations.  

[Tesla DeLorean]

Posted on March 02, 2017 at 21:50

Make sure to a) enable the FPU, and b) use the 32-bit float variants, the FPU doesn't do 64-bit doubles, or transcendentals like an 80x87 would.

If it still isn't fast enough, use tables.

[abarnett]

Posted on March 02, 2017 at 21:56

the sinf funtion reduced execution down to about 1us, very helpful and thanks.

Since I'm new to the chip (coming from a TI fixed point world) how do I know if the FPU is enabled?

Assuming it is, lookup tables will be next if the speed isn't enough.  Regardless, very helpful and thanks!!

[Tesla DeLorean]

Posted on March 02, 2017 at 21:58

In Keil it is a check box item (sets defines, etc), and then there is typically code in SystemInit() system_stm32f4xx.c

void SystemInit(void)

{ /* FPU settings ------------------------------------------------------------*/ &sharpif (__FPU_PRESENT == 1) && (__FPU_USED == 1) SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2)); /* set CP10 and CP11 Full Access */ &sharpendif

...

[abarnett]

Posted on March 02, 2017 at 22:14

I found the code you listed, confirmed that it's being executed, so I guess the FPU is active.  If the 1us execution is too long then I'll implement a look-up table.  

You've been very helpful Clive One, thanks!!