Need to count 32-bit value using LPT(low power timer)

[sujaigowda]

Hi all, I'm using Kinetis controller and ihave a question for lpt(low power timer). I'm using LPT as counter(counter and compare registers are 16-bit wide) and i need to count 32 bit value instead of 16 bit. can i cascaded the LPT?

[bendis]

Or, If you have only one LPTMR avaliable, you can set prescaler to 65536, count the upper 16 bits and then disable prescaler and count the lower 16 bits.

[sujaigowda]

Hi martin,

     I dint get your answer exactly. After i set prescaler, how to count? can you briefly tell us; it will be helpuful.

[bendis]

Hi!

Let's say you have uint32_t count value. What you need to do is to split counting in two steps:

1. First, you set prescaler in the PSR register to divide by 65536 and prescaler bypass PBYP to 0. Then you set the compare register CMR to (count >> 16) and start the timer.
2. Second, when you get the timer interrupt, you disable prescaler by setting PBYP to 1 and set the compare register CMR to (count & 0xFFFF) and again start the timer and wait for the interrupt.

In the first step you configure LPTMR to run 65536 times slower to count (count & 0xFFFF0000) clock cycles. Then you disable prescaler to count the remaining time - the lower 16 bits of your count value.

[sujaigowda]

Thank you martin. its a helpful answer.

[Carlos_Musich]

Hi Sujai,

It is possible. You can configure both timers, start one timer at any moment and then start the second timer inside the interrupts of the first timer. E.g.

int main(void)

{

    init_LPTMR0 ();

    init_LPTMR1 ();

    LPTMR0_CSR |= LPTMR_CSR_TEN_MASK;   //Turn on LPT and start counting

    while(1)

    {

    }

    return 0;

}

void LPTimer0_IRQHandler(void)

{

         LPTMR1_CSR |= LPTMR_CSR_TEN_MASK;   //Turn on LPT and start counting

}

Best regards,

Carlos

Technical Support Engineer

[sujaigowda]

Hi Carlos,

     Thank you for your reply. Yeah i was using same method in a different approach. i was trying to cascade it in hardware. Now im using same method and is working.

thank you carlos.

[Carlos_Musich]

Hi Sujai,

I am glad your problem was solved.

If you find our responses useful I encourage you to mark them as helpful or correct answer. This will help other members find the best answers as well.

Best regards,

Carlos

Technical Support Engineer