stm32F4 FPU Question

[terter etuet]

Posted on July 24, 2017 at 17:01

Hello,

i am trying to work with the fpu of the stm32f469-Disco and got some questions...

i am on ac6 systemworkbench/win7/

so far i can compile and run my app that uses float math...

when i look at the disassmbly it looks good: (as far as i can understand this, it uses the fpu-commands vadd.f32, vmul.f32 etc)

0800c842:   beq.n   0x800c8cc <main()+588>

 545              test = 1.0f / (float)(ix%4) + test;0800c844:   ldrh    r3, [r7, #50]   ; 0x320800c846:   uxth    r3, r30800c848:   and.w   r3, r3, #30800c84c:   vmov    s15, r30800c850:   vcvt.f32.s32    s15, s150800c854:   vmov.f32        s13, #112       ; 0x700800c858:   vdiv.f32        s14, s13, s150800c85c:   vldr    s15, [r7, #44]  ; 0x2c0800c860:   vadd.f32        s15, s14, s15etc

but:

__FPU_USED is 0 because __VFP_FP__ is not defined (core_cm4.h line 149)

and SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2));  /* set CP10 and CP11 Full Access */

doesent get set

SystemInit(void){

  #if (__FPU_PRESENT == 1) && (__FPU_USED == 1)

    SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2));  /* set CP10 and CP11 Full Access */  #endif

....

}

shouldent this generate a FPU-FAULT?

and where can i define __VFP_FP__ ?  putting in

dident help...

many thanks for some enlightment!

[Tesla DeLorean]

Posted on July 24, 2017 at 17:16

Check for

SCB->CPACR 

code in the Reset_Handler, that's typically where I'd put it.

[waclawek.jan]

Posted on July 24, 2017 at 19:01

 ,

 ,

+1

Instead of hunting down an infinite chain of ♯ defines stemming from obscure system headers and some even directly from cc1, I too chose to enable the FPU myself 'manually'.

Sometimes overautomation hurts.

JW

[Tesla DeLorean]

Posted on July 24, 2017 at 20:19

; Reset handler
Reset_Handler PROC
 EXPORT Reset_Handler [WEAK]
 IMPORT SystemInit
 IMPORT __main
 ;FPU settings
 LDR R0, =0xE000ED88 ; Enable CP10,CP11
 LDR R1,[R0]
 ORR R1,R1,#(0xF << 20)
 STR R1,[R0]
 LDR R0, =SystemInit
 BLX R0
 LDR R0, =__main
 BX R0
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