Due: Write to digital pin when ADC is running

Question

I have a problem writing to a digital pin on Arduino Due while my ADC is running.

I have the following code:

 #undef HID_ENABLED
// Arduino Due ADC->DMA->USB 1MSPS
// by stimmer
// from http://forum.arduino.cc/index.php?topic=137635.msg1136315#msg1136315
// Input: Analog in A0
// Output: Raw stream of uint16_t in range 0-4095 on Native USB Serial/ACM
// on linux, to stop the OS cooking your data: 
// stty -F /dev/ttyACM0 raw -iexten -echo -echoe -echok -echoctl -echoke -onlcr
// source: https://gist.github.com/pklaus/5921022
// applied patch 1 from: http://forum.arduino.cc/index.php?topic=137635.msg2526475#msg2526475
// applied patch 2 from: https://gist.github.com/pklaus/5921022 comment on Apr 2, 2017 from borisbarbour
volatile int bufn,obufn;
uint16_t buf[4][256]; // 4 buffers of 256 readings
void ADC_Handler(){ // move DMA pointers to next buffer
 int f=ADC->ADC_ISR;
 if (f&(1<<27)){
 bufn=(bufn+1)&3;
 // patch 2 start
 //ADC->ADC_RNPR=(uint32_t)buf[bufn];
 ADC->ADC_RNPR=(uint32_t)buf[(bufn+1)&3];
 // patch 2 end
 ADC->ADC_RNCR=256;
 } 
}
void setup() {
 SerialUSB.begin(0);
 while(!SerialUSB);
 pmc_enable_periph_clk(ID_ADC);
 adc_init(ADC, SystemCoreClock, ADC_FREQ_MAX, ADC_STARTUP_FAST);
 ADC->ADC_MR |=0x80; // free running
 ADC->ADC_CHER=0x80; 
 NVIC_EnableIRQ(ADC_IRQn);
 ADC->ADC_IDR=~(1<<27);
 ADC->ADC_IER=1<<27;
 ADC->ADC_RPR=(uint32_t)buf[0]; // DMA buffer
 ADC->ADC_RCR=256;
 ADC->ADC_RNPR=(uint32_t)buf[1]; // next DMA buffer
 ADC->ADC_RNCR=256;
 // patch 1.2 start
 //bufn=obufn=1;
 bufn=1;
 obufn=0;
 // patch 1.2 end
 ADC->ADC_PTCR=1;
 ADC->ADC_CR=2;
 // this doesn't work:
 pinMode(52, OUTPUT); // 
 digitalWrite(52, HIGH); //
}
void loop(){
 // patch 1.1 start
 while((obufn + 1)%4==bufn);// wait for buffer to be full
 // patch 1.1 end
 SerialUSB.write((uint8_t *)buf[obufn],512); // send it - 512 bytes = 256 uint16_t
 obufn=(obufn+1)&3; 
}

Pin 52 says 0 V.

With this function, I can pull the digital output voltage to 1.58 V:

void digitalWriteDirect(int pin, boolean val){
 if(val) g_APinDescription[pin].pPort -> PIO_SODR = g_APinDescription[pin].ulPin;
 else g_APinDescription[pin].pPort -> PIO_CODR = g_APinDescription[pin].ulPin;
}

Any ideas?

Answer 1

I found the problem: The Arduino had been waiting for the SerialUSB Connection.

The Serial connection has not been established because I was running the Arduino without running the corresponding Python script. That script would have opened the Serial connection.

When running the Python script, the Arduino Due then works as expected.