Kinetis MicrocontrollersのトピックRe: To get the algorithm time.

To get the algorithm time.

vipindas — Mon, 30 Mar 2015 16:29:58 GMT

Hi,

I am using a K60 twr board, and i have a delay function like this.

void delay()

{

unsigned int i, n;

for(i=0;i<1000;i++)

{

asm("nop");

}

When i checked the number of cpu cycles (using the systick) it takes,it showed around 3000, which is theoretically correct (optimized code for speed, so 1000nop + 1000 add + 1000 cmp)

Since my cpu is 120Mhz, if i set and reset a gpio before and after calling this delay, i expect

theoritically -> 3000 cpu cycles X 0.0083micro seconds = 25 micro seconds

but, practically (by setting and resetting gpio) i am seeing it as around 143 micro seconds.

Any idea why this difference? I am really running my core @ 125?, or is my calcultion wrong somewhere?

My systick configurtaio

SYST_RVR = 0xFFFFFFFF;

SYST_CSR = 0x7;

int nStart = SYST_CVR;

delay()

int nStop = SYST_CVR;

thanks in advance

Re: To get the algorithm time.

jeremyzhou — Tue, 31 Mar 2015 00:34:32 GMT

Hi Vipindas,

Thank you very much for your focus on Freescale Kinetis product. I'm glad to provide service for you.

And I'd like to suggest that you should get the corresponding assembly instruction when you debug the set and reset a GPIO with the delay function in IDE.

I think it will give you more detail about the code execute operation.
Have a great day,

Ping

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Re: To get the algorithm time.

vipindas — Tue, 31 Mar 2015 14:59:41 GMT

Hi,

pls find the routine attached

c code

while(1) {

toggle led();

delay();

}

Assembly routine

delay:

1fff02b6: nop

1fff02b8: subs r0,r4,#1

1fff02ba: nop

1fff02bc: subs r4,r0,#1

1fff02be: bne delay (0x1fff02b6) ; 0x1fff02b6

1fff02c0: b main+0x38 (0x1fff0294) ; 0x1fff0294

1fff02c2: nop

exit:

Re: To get the algorithm time.

vipindas — Tue, 31 Mar 2015 15:00:52 GMT

delay routine

void delay()

{

unsigned int i, n;

for(i=0;i<1000;i++)

{

asm("nop");

}

Re: To get the algorithm time.

jeremyzhou — Wed, 01 Apr 2015 08:08:12 GMT

Hi Vipindas,

According your statement, I'd like to confirm one things with you.

Was the 143 ms the period of the pin swing?

Did you ever use the oscilloscope capture the signal?
Have a great day,
Ping

Re: To get the algorithm time.

vipindas — Wed, 01 Apr 2015 13:36:35 GMT

Yes, i used the oscilloscope to measure the timings and the timings between pin swing is 143 micro seconds (not milli seconds).

Re: To get the algorithm time.

yasuhikokoumoto — Wed, 01 Apr 2015 23:36:49 GMT

Hello vipindas,

how much time does it take for execution without the delay() function?

Isn't it around 120 micro seconds?

Best regards,

Yasuhiko Koumoto.