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Trigger ADC from Timer Match
Topic last updated 31 Jan 2013, by 
Matias Bevilacqua.
27
replies
Matias Bevilacqua.
27
replies
Hi,
I'm puzzled about how to hardware trigger the ADC (in burst mode) from a Timer1 Match.
I tried Andy's DMA which worked like charm but has drawbacks on getting nice intervals as the conversion time is 65 cycles and the clock is derived from 96Mhz you cannot get an exact int number of ms for timing.
So my next bet is either Timer1 or the Repetitive Timer.
So the question: how do i connect this code to trigger the ADC in burst mode (need to convert two channels). I know I can software trigger from inside the timer interrupt routine but I would like to remove the timer interrupt handler al together and have the adc triggered by hardware.
Got the following code (ripped from a larger program) that I wrote to verify timer1 timing. I verified that it does have a nearly exact 10ms interval I want.
//------------------------------------------------------------------------------ //----TIMER1. //------------------------------------------------------------------------------ volatile unsigned int timer1hits = 0; //timer1 stops when timer1hits==imer1loop unsigned long match = 10000-1; //10ms (1Mhz/10000) unsigned int timer1loop = 1000; //nosamples unsigned long prescaler = 96-1; //96Mhz/96 = 1Mhz //Resulting timing 1000 hits 9999.99900 ms. //Ideal 10000.00000 ms ie a -0,001 % deviation Timer match_timing; //DigitalOut cap_led(LED2); void Timer1_IRQHandler(void) { LPC_TIM1->MR0 = match; LPC_TIM1->IR = 1; //cap_led=!cap_led; timer1hits++; //TODO Debug Code (stop after timer1loop samples)... if (timer1hits==timer1loop) { match_timing.stop(); LPC_TIM1->TCR = 0; // Disable Timer } }This is called from a modified piece of code found on this forum:
// Enable the ISR vector NVIC_SetVector (TIMER1_IRQn, (uint32_t)&Timer1_IRQHandler); NVIC_EnableIRQ(TIMER1_IRQn); // Set PCLK_TIMER1 // PCLK_TIMER1 = CCLK/1 96M/1 = 96MHz LPC_SC->PCLKSEL0 &= ~(3UL << 4); //clear bits LPC_SC->PCLKSEL0 |= (1UL << 4); //set bit //Reset Test Variable. timer1hits = 0; LPC_SC->PCONP |= 1 << 2; // Power on Timer 1 LPC_TIM1->TCR = 0x2UL; // Reset and set to timer mode LPC_TIM1->CTCR = 0x0; // Connect to prescaler LPC_TIM1->PR = prescaler; // Prescale -> 1Mhz LPC_TIM1->MR0 = match; // Match count for 10mS LPC_TIM1->MCR = 3; // Interrupt and Reset on Match LPC_TIM1->TCR = 0x1UL; // Enable Timer match_timing.start(); //Pause 10 seconds. while (LPC_TIM1->TCR==1) { // wait(0.1); } //Moved code to interrupt routine. //LPC_TIM1->TCR = 0; // Disable Timer //match_timing.stop(); printf("%d hits\r\n", timer1hits); printf("%f ms\r\n", 0.001*match_timing.read_us()); match_timing.reset(); }