Time taken for a fuction

Marcelo Gutierrez

Prodigy 155 points

Hi all,

I wonder why the time (round trip) taken, when call a function, to travel from ARM to DSP and back to ARM is 150uS?

The procedure followed to get the round trip time:

1) I got 2 functions: call_arm()(ARM<--->ARM) and call_dsp()(ARM<--->DSP). (They are empty functions)

2) The main function calls the functions "call_dsp()" and call_arm()

3) Measured the time elapsed for each function.

Results:

Nx	call_arm()	call_dsp()
1	8uS	154uS
2	8uS	165uS
3	8uS	149uS
4	9uS	149uS
5	7uS	149uS

Can I reduce call_dsp's latency ?

Regards,

over 11 years ago

0 Cvetolin Shulev-XID over 11 years ago

TI__Guru 65405 points

Hi Marcelo,

Could you post the source of call_arm() and call_dsp() functions and how call them?

Tsvetolin Shulev

0 Marcelo Gutierrez over 11 years ago in reply to Cvetolin Shulev-XID

Prodigy 155 points

main.c(Running on ARM)

typedef unsigned long long timestamp_t;
 
timestamp_t get_timestamp()
{
    struct timeval now;
    gettimeofday(&now, NULL);
    return now.tv_usec + (timestamp_t)now.tv_sec*1000000;
}

void main(){
.
.
.
// Call data process function from  ARM to DSP(C6RUN)
	t_arm_dsp = get_timestamp();
	data_process_dsp(void);
	t_arm_dsp = get_timestamp() - t_arm_dsp;//don't consider the overhead


// Call data process function from ARM to ARM
	t_arm = get_timestamp();
	data_process_arm(void);
	t_arm = get_timestamp() - t_arm; //don't consider the overhead

    printf("\tNX = %d   \tARM: %d   \tARM_DSP: %d\n", nx, (int)t_arm, (int)t_arm_dsp);


}

data_process_dsp.c

void data_process_dsp(void)
{
//empty function
return 0
}

data_process_arm.c

void data_process_arm(void)
{
//empty function
return 0
}

0 Cvetolin Shulev-XID over 11 years ago in reply to Marcelo Gutierrez

TI__Guru 65405 points

Hi Marcelo,

After seeing the source code I can not find nothing that could add some delay the communication between the ARM and DSP is based on hardware interrupts, mail boxes and exchange of messages which take some time. Probably the response of the DSP is slower then the ARM.

Tsvetolin Shulev

0 Marcelo Gutierrez over 11 years ago in reply to Cvetolin Shulev-XID

Prodigy 155 points

Hi Tsvetolin,

I appreciate your quick response!.

I've concluded that if I call a function from DSP to DSP is faster than ARM to DSP.

main.c(Running on ARM)

typedef unsigned long long timestamp_t;
 
timestamp_t get_timestamp()
{
    struct timeval now;
    gettimeofday(&now, NULL);
    return now.tv_usec + (timestamp_t)now.tv_sec*1000000;
}

void main(){
.
.
.
// Call data process function from  ARM to DSP(C6RUN)
	t_arm_dsp = get_timestamp();
	data_process_dsp(void);
	t_arm_dsp = get_timestamp() - t_arm_dsp;//don't consider the overhead

// Call data process function from  ARM to DSP and then DSP to DSP (C6RUN)
	
	t_dsp=data_dsp_dsp(void);
	

// Call data process function from ARM to ARM
	t_arm = get_timestamp();
	data_process_arm(void);
	t_arm = get_timestamp() - t_arm; //don't consider the overhead

    printf("\tNX = %d   \tARM: %d  \tDSP: %d \tARM_DSP: %d\n", nx, (int)t_arm,(int)t_dsp, (int)t_arm_dsp);


}

data_dsp_dsp.c (Running on the DSP)

int data_dsp_dsp(void){
	
        clock_t t_dsp;
    
	t_dsp = clock();
	data_process_dsp(void);
	t_dsp = clock() - t_dsp;
    
 	return t_dsp;
}

data_process_dsp.c (Running on the DSP)

void data_process_dsp(void)
{
//empty function
return 0
}

Results-DM3730:

Nx	ARM<-->ARM	DSP<-->DSP	ARM<-->DSP
1	8uS	980nS	153uS
2	8uS	982nS	150uS
3	9uS	979nS	149uS
4	7uS	979nS	149uS
5	8uS	980nS	149uS

0 Cvetolin Shulev-XID over 11 years ago in reply to Marcelo Gutierrez

TI__Guru 65405 points

Hi Marcelo,

Thanks for sharing the data of measuring the time for calling functions ARM<-->ARM, DSP<-->DSP and ARM<-->DSP. As I expect the calling DSP function from the DSP is fastest because in this case there is no exchange of messaging.

Tsvetolin Shulev

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Time taken for a fuction