Triggering ADC with PDB in Teensy 3.6

Bert62 · Jun 6, 2020

Hello all,

I am trying to trigger ADC0 of the Teensy 3.6 with the PDB. I want 2 measurements per PWM period, so I have used FTM3 as a trigger input to PDB0 with 2 pretriggers. The delay of PDB0_CH0DLY0 is 0 while the delay of PDB0_CH0DLY1 is MOD/2.

This is all working correctly. However, I have a weird issue. ADC0 always makes 2 conversions for each trigger, so I get 4 measurements, 2 of which are redundant. To put it simply, ADC0_SC1A and ADC0_SC1B always convert together for each pretrigger.

I have the code of FTM3, PDB and ADC0 below respectively. [Note: MOD value is equal to 599 while Phi is equal to 200.]

Code:

void initFTM3(void) {
  SIM_SCGC3    |= 0x02000000; 

  FTM3_SC      = 0x00;     
  FTM3_CONF    = 0xC0;   
  FTM3_FMS     = 0x00; 
  FTM3_MODE   |= 0x05;

  FTM3_C0SC     = 0x28;         
  FTM3_C1SC     = 0x28;  
  FTM3_C2SC     = 0x28;
  FTM3_C3SC     = 0x28;

  FTM3_C4SC     = 0x68;
  FTM3_C5SC     = 0x28;

  FTM3_COMBINE  = 0x030303;
  FTM3_COMBINE |= 0x1010;
  FTM3_COMBINE |= 0x202020;
  FTM3_DEADTIME = 0x00;

  FTM3_CNT      = 0x00;          
  FTM3_CNTIN    = 0x00;          
  FTM3_MOD      = MOD;           
  FTM3_SYNC     = 0x02;            
  FTM3_SC       = 0x28;          

  PORTD_PCR0    = 0x400;          
  PORTD_PCR1    = 0x400;          
  PORTD_PCR2    = 0x400;          
  PORTD_PCR3    = 0x400;      

  PORTC_PCR8    = 0x300;          
  PORTC_PCR9    = 0x300;          
  
  FTM3_C0V      = (MOD+1)/2 - Phi;
  FTM3_C1V      = (MOD+1)/2;
  FTM3_C2V      = 0;
  FTM3_C3V      = (MOD+1) - Phi;

  FTM3_C4V      = ((MOD+1) - Phi)/2 - 8; 
  FTM3_C5V      = (2*(MOD+1) - Phi)/2 - 8;

  FTM3_EXTTRIG |= 0x04; 
  asm("nop");
}

Code:

void initPDB0(void) {
  SIM_SCGC6    |= 0x400000;     
  PDB0_CNT      = 0;         
  PDB0_MOD      = MOD;      

  PDB0_CH0C1   |= 0x303;    
  PDB0_CH0DLY0  = 0;       
  PDB0_CH0DLY1  = (MOD+1)/2;    
  
  PDB0_SC       = 0xBA1; 
}

Code:

void initADC0(void) {
  SIM_SCGC6    |= 0x08000000; 
  SIM_SOPT7     = 0x00;
  ADC0_CFG1     = 0x04;
  ADC0_CFG2     = 0x04;           
  ADC0_SC2      = 0x40;        
  ADC0_SC3      = 0x00;       
  ADC0_SC1A     = 0x4C;       
  ADC0_SC1B     = 0x51; 

  NVIC_SET_PRIORITY(IRQ_ADC0, 128);
  NVIC_CLEAR_PENDING(IRQ_ADC0) |= 1<<7;
  NVIC_ISER1                   |= 1<<7;
  NVIC_ENABLE_IRQ(IRQ_ADC0);
  asm("cpsie i");                  
}

Below is the ISR of ADC0 to read measurements from the results registers ADC0_RA and ADC0_RB.

Code:

void adc0_isr(void) {
  bool control = true;
  
  if (ADC0_SC1A & 0xCC) {
    V_analog[0] = ADC0_RA;  
    V_o = VoutScale*V_analog[0];
    operation();
    control = !control;
  }

  if (ADC0_SC1B & 0xD1) {
    V_analog[0] = ADC0_RB; 
    V_in = VinScale*V_analog[0];
    control = !control;
  }

  Serial.println(control);
  asm("nop");
}

The value of the variable control is always TRUE, which means it is toggled twice for each pretrigger which means ADC0_SC1A and ADC0_SC1B convert twice. I want just one conversion per pretrigger.

Does anyone know why this happens? Is there something I missed in the initialization or if I have a mistake in the code?

Thanks in advance.

Triggering ADC with PDB in Teensy 3.6

Bert62

Member