Kinetis Microcontrollers中的主题 Re: How to use DSP instructions on Kinetis K66 MCU?

How to use DSP instructions on Kinetis K66 MCU?

giova841 — Tue, 21 Feb 2017 18:02:51 GMT

Hi everybody,

I have written a program on the K65 MCU which performs some controls and a few calculations. Looking at execution times I found out that the calculations performed were the instructions that took the most time.

These calculations are simple multiplications between float variables and I think that some micro-seconds for each multiplication is really too high, considering I have a 120 MHz clock! probably there is something missing in my code or there are some compiler options which I have not set properly so I am asking you:

is there any compiling options I can enable in order to use the math co-processro provided with the ARM -M4?
is there any libraryI can laod to use the "DSP Instructions" described in the ARM -M4 reference guide?

Cheers,

Giulio

Re: How to use DSP instructions on Kinetis K66 MCU?

mjbcswitzerland — Tue, 21 Feb 2017 18:20:43 GMT

Do you compiler for HW FPU use?

These flags are needed by GCC:

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

Regards

Mark

Re: How to use DSP instructions on Kinetis K66 MCU?

giova841 — Tue, 21 Feb 2017 21:36:43 GMT

Yes, these are my compiler settings:

Re: How to use DSP instructions on Kinetis K66 MCU?

Hui_Ma — Mon, 27 Feb 2017 08:22:20 GMT

Besides to set the compiler, it also need to enable FPU with below code:

; Enable the floating point coprocessor

#if defined (_VFPv4_)

MOVW r1,#60808 ; load CPACR

MOVT r1,#57344 ; (0xE000ED88)

LDR r0,[r1]

ORR.W r0,r0,#VFPEnable ; Enable FPU

STR r0, [r1] ; on CP10, CP11

MOV.W r0,#R2N_Enable

VMSR FPSCR, r0

#endif

Wish it helps.

Have a great day,
Ma Hui
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