// Method 1: Polling
main()
{
    uint8_t count = 0;
    ..
    ..
    while(posedge_input) {
        count++;
        if(count == 0) {
            // Start timer
        }
        else if(count == 7) {
            // Stop, Read and Reset timer value
            count = 0;
        }
    }
    ..
    ..
}

// Method 2: Hardware Interrupt
// You'll have to read the datasheet for this, I don't have any tutorial for this yet.

uint8_t count = 0;      // Global counter

Hardware_Interrupt_ISR()
{
    if(posedge_input) {
        count++;
        if(count == 0) {
            // Start timer
        }
        else if(count == 7) {
            // Stop, Read and Reset timer value
            count = 0;
        }
    }
}

main()
{
    ..
    ..
    // Do general initialization
    ..
}