Issue w/ AnalogRead in Interrupt

[daanstevenson]

Hi Khoi,
Thanks for writing and sharing this timer interrupt library.
I am trying to implement consistently spaced sampling on a Nano33BLE, but the board seems to crash whenever I have a call to analogRead within the ISR.

Arduino IDE version: 1.8.13
Arduino mbed Nano Core Version 2.4.1
OS: Windows 10

Minimal code is below. I have also tried with an Adafruit nrf52 board and your other version of the library. This seems to work, but only if interrupts are halted before the analogRead call and enabled afterwards.

Working on native Nordic SDK firmware, but it would be great to accelerate prototyping with your library!

// test of timer ADC functionality

#include "NRF52_MBED_TimerInterrupt.h"

#define MOTOR_PIN P0_27 // 9u, D9
#define OPTO_PIN P0_21 // 8u, D8
#define FIELD_MILL_PIN P0_5 // 15u, A1

#define SAMPLE_INTERVAL 500
#define BLE_INTERVAL 10000

NRF52_MBED_Timer sample_timer(NRF_TIMER_4);
NRF52_MBED_Timer ble_timer(NRF_TIMER_3);

volatile int idx;
volatile unsigned long times[20] = {};
volatile int readings[20] = {};
volatile int fm_output = 0;

unsigned long t_now; // start time for current loop
unsigned long t_last_sample = 0;
unsigned long sample_delay = 5000;
unsigned long t_last_print = 0;
unsigned long print_delay = 500E3;

void setup() {
// put your setup code here, to run once:

Serial.begin(57600);

analogReadResolution(12);

sample_timer.attachInterruptInterval(SAMPLE_INTERVAL, SampleTimerFunc);
ble_timer.attachInterruptInterval(BLE_INTERVAL, BleTimerFunc);

}

void loop() {
// put your main code here, to run repeatedly:

t_now = micros();
// if (t_now - t_last_sample > sample_delay)
// {
// t_last_sample = t_now;
// times[idx] = micros();
// readings[idx] = analogRead(FIELD_MILL_PIN);
// idx++;
// if (idx >= 20)
// {
// idx = 0;
// }
// }

// Print debug data
if (t_now - t_last_print > print_delay)
{
t_last_print = t_now;
Serial.println(fm_output);
for (int i = 0; i < 20; i++)
{
Serial.print(times[i]);
Serial.print("\t");
}
Serial.println();
for (int i = 0; i < 20; i++)
{
Serial.print(readings[i]);
Serial.print("\t");
}
Serial.println();
}
}

void SampleTimerFunc()
{
times[idx] = micros();
// noInterrupts();
readings[idx] = analogRead(FIELD_MILL_PIN);
// interrupts();
// readings[idx] = 200;

idx++;
if (idx >= 20)
{
idx = 0;
}
}

void BleTimerFunc()
{
int total = 0;
for (int i = 0; i < 20; i++)
{
total += readings[i];
}
fm_output = (int)(76.0 * (double)total / 20.0);
}

[khoih-prog]

As a rule, you can't do something too long in ISR, especially using the messy analogRead().

The correct way to do is set a flag inside ISR, then call analogRead() outside ISR using a loop depending on millis().

Also have a look at analogRead #2

Thanks for your interest in the library.

Good Luck,