I have success!
(oops, that's suppose to be Timer1)
I only sample for 1/60 of a second. What I did was to back up all the timer registered I used and then resorted them after I was done sampling. (As opposed to initializing the registers in setup and then starting the timer when needed.)
Now I have a Nano sampling the data and sending it to a MySensors Gateway on an RPi3B+ which then sends it to an MQTT broker runing on an old laptop. Also running on the laptop is Home Assistant running inside of VirtualBox.
If MySensors does use Timer1, it appears that restoring the registers allows it to be shared.
//------------------------------------------------------ISR
ISR(TIMER1_OVF_vect){ // interrupt service routine for overflow
TCNT1 = TimerPreloadValue; // must be first line! starts the timer counting again
digitalWrite(TRIGGER_START_SAMPLE_PIN,HIGH);
samplesVolts[--sample]=analogRead(VOLTS_IN_PIN); // decrement before capturing
samplesCurrent[sample]=analogRead(CURRENT_IN_PIN);
digitalWrite(TRIGGER_START_SAMPLE_PIN,LOW);
if (!sample){ // count down to zero
digitalWrite(TRIGGER_START_SAMPLE_PERIOD_PIN,LOW); // indicate that sampling is complete
samplingEnd = micros();
TCCR1B &= 248; // turns off timer
}
}
//------------------------------------------------------sampleOneCycle
void sampleOneCycle(){
// back up timer registers
uint8_t TCNT1_b = TCNT1;
uint8_t TCCR1B_b = TCCR1B;
uint8_t TCCR1A_b = TCCR1A;
uint8_t TIMSK1_b = TIMSK1;
// configure timer which starts the sampling
noInterrupts(); // disable all interrupts
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = TimerPreloadValue; // preload timer
//TCCR1B |= (1 << CS10)|(1 << CS12); // 1024 prescaler
TCCR1B &= 248; // turns off timer?
TIMSK1 |= (1 << TOIE1); // enable timer overflow interrupt ISR
// demark sampling
sample = NUMBER_OF_SAMPLES; // count down to zero
digitalWrite(TRIGGER_START_SAMPLE_PERIOD_PIN,HIGH);
samplingStart = micros();
TCNT1 = 65535; // first trigger right away!
TCCR1B |= 1; // turns on timer
interrupts(); // enable all interrupts
// wait for sampling to be complete
while(digitalRead(TRIGGER_START_SAMPLE_PERIOD_PIN)){};
samplingEnd = micros();
// restore timer registers
TCNT1 = TCNT1_b;
TCCR1B = TCCR1B_b;
TCCR1A = TCCR1A_b;
TIMSK1 = TIMSK1_b;
}
