CCS/TMS570LS1224: how fast can microcontroller respond to an interrupt?

Hamid Kavian Athar

Tool/software: Code Composer Studio

Hi there

I want to send and receive data with mibspi interface. the tms570 acts as slave. there are 2 us time between two consequtive transaction. the cpu is working with a 160 MHz clock. so the there is 320 cycles between two transaction.as much as I know the interrupt latency on cortex R CPUs are very low (less than 20 cycles). but when I write some code in mibspi I lose some interrupts. I don't think my code takes more than 10 cycle. this is my ISR. I have set the length of buffer of transfer group to 1.

void mibspiGroupNotification(mibspiBASE_t *mibspi, uint32 group)
{
/* enter user code between the USER CODE BEGIN and USER CODE END. */
/* USER CODE BEGIN (27) */

mibspiRAM3->tx[0].data = LUT[mibspiRAM3->rx[0].data];

/* USER CODE END */
}

thank a lot.

over 7 years ago

0 QJ Wang over 7 years ago

TI__Guru**** 201386 points

Hello Hamid,

Please refer to this post:

0 Hamid Kavian Athar over 7 years ago in reply to QJ Wang

Intellectual 550 points

Hi Mr Wang

thanks for the comment. I also have measured interrupt latency of mibspi for many times. I have initialized pmu and in infinite loop I have reset it and in mibspi isr the counter value is read. these are the measure values:

192
214
518
816
1114
1412
1710
178
476

as you see these values are too large for my application.

this my isr:

void mibspiGroupNotification(mibspiBASE_t *mibspi, uint32 group)
{
/* enter user code between the USER CODE BEGIN and USER CODE END. */
/* USER CODE BEGIN (27) */

time[index++] = _pmuGetCycleCount_();
mibspiRAM3->tx[0].data = LUT[mibspiRAM3->rx[0].data];//aun8TXBuffer1[0];
/*

}

and in main function I have written this code:

int main()

{

[...]

_pmuInit_();
_pmuStartCounters_(pmuCYCLE_COUNTER);

[...]

while(1)
{
_pmuResetCounters_();
}

[...]

thanks.

0 QJ Wang over 7 years ago in reply to Hamid Kavian Athar

TI__Guru**** 201386 points

Hello Hamid,

Your code doesn't show where you start the PMU cycle counter and where you stop the PMU cycle counter.

0 Hamid Kavian Athar over 7 years ago in reply to QJ Wang

Intellectual 550 points

I have started the counter after its initialization then in while loop I am reseting it. finally in spi isr I read the counter value.

0 QJ Wang over 7 years ago in reply to Hamid Kavian Athar

TI__Guru**** 201386 points

Hi Hamid,

1. When you start the counter in while() loop, the interrupt might not be trigger at that moment. So the measurement is not accurate.

2. Before reading the counter, please stop counter first.

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CCS/TMS570LS1224: how fast can microcontroller respond to an interrupt?