SAMD51: analogWrite on A5 not working after editing variant file

Dimitree · May 28, 2024, 1:02pm

I made a custom board based on ATSAMD51J19, and used the variant files from Adafruit Hallowing M4 (variant files) as starting point for my custom variant files.
After editing the variant files, I noticed that the ADC on PORTA-4 was not returning correct values.
So I noticed that "analogRead(A5)" returns always the same value.
Every other pin (ADC, DAC, USB, Serial, digital pins) is working fine.
Reverting back to the original variant files fixes the issue, so I'd say the hardware is fine, and there should be something wrong in my variant files.

I can't find any difference in how A5 is defined in both the original variant file and in my edited version, except for the order in the "g_APinDescription" array, so I really don't understand what is happening.

this is the simple sketch that I'm using for testing the issue:

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println(analogRead(A5));
}

I got the same results if I use "analogRead(4)" instead of "analogRead(A5)".
Those are my complete variant files:

#ifndef _VARIANT_HALLOWING_M4_
#define _VARIANT_HALLOWING_M4_

#define ARDUINO_SAMD_VARIANT_COMPLIANCE 10610

#define VARIANT_MAINOSC		(32768ul)

#define VARIANT_MCK	   (F_CPU)

#define VARIANT_GCLK0_FREQ (F_CPU)
#define VARIANT_GCLK1_FREQ (48000000UL)
#define VARIANT_GCLK2_FREQ (100000000UL)

#include "WVariant.h"

#ifdef __cplusplus
#include "SERCOM.h"
#include "Uart.h"
#endif

#ifdef __cplusplus
extern "C"
{
#endif

#define PINS_COUNT           (50u)
#define NUM_DIGITAL_PINS     (50u)
#define NUM_ANALOG_INPUTS    (4u)
#define NUM_ANALOG_OUTPUTS   (2u)
#define analogInputToDigitalPin(p)  (p)

#define digitalPinToPort(P)        ( &(PORT->Group[g_APinDescription[P].ulPort]) )
#define digitalPinToBitMask(P)     ( 1 << g_APinDescription[P].ulPin )
#define portOutputRegister(port)   ( &(port->OUT.reg) )
#define portInputRegister(port)    ( &(port->IN.reg) )
#define portModeRegister(port)     ( &(port->DIR.reg) )
#define digitalPinHasPWM(P)        ( g_APinDescription[P].ulPWMChannel != NOT_ON_PWM || g_APinDescription[P].ulTCChannel != NOT_ON_TIMER )

#define PIN_A0               (2ul)
#define PIN_A1               (5ul)
#define PIN_A2               (7ul)
#define PIN_A3               (6ul)
#define PIN_A4               (8ul)
#define PIN_A5               (4ul)
#define PIN_DAC0             PIN_A0
#define PIN_DAC1             PIN_A1
static const uint8_t A0 = PIN_A0;
static const uint8_t A1 = PIN_A1;
static const uint8_t A2 = PIN_A2;
static const uint8_t A3 = PIN_A3;
static const uint8_t A4 = PIN_A4;
static const uint8_t A5 = PIN_A5;
static const uint8_t DAC0 = PIN_DAC0;
static const uint8_t DAC1 = PIN_DAC1;
#define ADC_RESOLUTION		12

// Serial1
#define PIN_SERIAL1_RX       (12ul)
#define PIN_SERIAL1_TX       (13ul)
#define PAD_SERIAL1_RX       (SERCOM_RX_PAD_1)
#define PAD_SERIAL1_TX       (UART_TX_PAD_0)

// Serial2
#define PIN_SERIAL2_RX       (23ul)
#define PIN_SERIAL2_TX       (22ul)
#define PAD_SERIAL2_RX       (SERCOM_RX_PAD_1)
#define PAD_SERIAL2_TX       (UART_TX_PAD_0)

//USB
#define PIN_USB_HOST_ENABLE (49ul)
#define PIN_USB_DM          (24ul)
#define PIN_USB_DP          (25ul)

#ifdef __cplusplus
}
#endif

#ifdef __cplusplus
extern SERCOM sercom0;
extern SERCOM sercom1;
extern SERCOM sercom2;
extern SERCOM sercom3;
extern SERCOM sercom4;
extern SERCOM sercom5;
extern Uart Serial1;
extern Uart Serial2;
#endif

#define SERIAL_PORT_USBVIRTUAL      Serial
#define SERIAL_PORT_MONITOR         Serial
#define SERIAL_PORT_HARDWARE        Serial1
#define SERIAL_PORT_HARDWARE_OPEN   Serial1

#endif

#include "variant.h"

const PinDescription g_APinDescription[]=
{
  { PORTA,  0, PIO_SERCOM_ALT, PIN_ATTR_PWM_E, No_ADC_Channel, TC2_CH0, TC2_CH0, EXTERNAL_INT_0 },          
  { PORTA,  1, PIO_SERCOM_ALT, PIN_ATTR_PWM_E, No_ADC_Channel, TC2_CH1, TC2_CH1, EXTERNAL_INT_1 },          
  { PORTA,  2, PIO_ANALOG,  PIN_ATTR_ANALOG, DAC_Channel0, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_2 },      
  { PORTA,  3, PIO_DIGITAL, PIN_ATTR_ANALOG, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
  { PORTA,  4, PIO_ANALOG,  PIN_ATTR_ANALOG, ADC_Channel4, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_4 },      
  { PORTA,  5, PIO_ANALOG,  PIN_ATTR_ANALOG, DAC_Channel1, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_5 },      
  { PORTA,  6, PIO_ANALOG,  PIN_ATTR_ANALOG, ADC_Channel6, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_6 },      
  { PORTA,  7, PIO_ANALOG,  PIN_ATTR_ANALOG, ADC_Channel7, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_5 },      
  { PORTA,  8, PIO_ANALOG,  PIN_ATTR_ANALOG, ADC_Channel8, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTA,  9, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTA, 10, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTA, 11, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTA, 12, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, TC2_CH0, TC2_CH0,  EXTERNAL_INT_12 }, 
  { PORTA, 13, PIO_SERCOM_ALT, PIN_ATTR_PWM_E, No_ADC_Channel, TC2_CH1, TC2_CH1,  EXTERNAL_INT_13 },
  { PORTA, 14, PIO_DIGITAL, PIN_ATTR_PWM_E, No_ADC_Channel, TC3_CH0, TC3_CH0, EXTERNAL_INT_14 },
  { PORTA, 15, PIO_DIGITAL, PIN_ATTR_PWM_E, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_15  },
  { PORTA, 16, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_0  },  
  { PORTA, 17, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_1 },   
  { PORTA, 18, PIO_DIGITAL, PIO_SERCOM, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_2  },        
  { PORTA, 19, PIO_DIGITAL, PIN_ATTR_PWM_E, No_ADC_Channel, TC3_CH1, TC3_CH1,  EXTERNAL_INT_3 },  
  { PORTA, 20, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER,  EXTERNAL_INT_4 },  
  { PORTA, 21, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER,  EXTERNAL_INT_5 },
  { PORTA, 22, PIO_SERCOM,  PIN_ATTR_PWM_G, No_ADC_Channel, TCC0_CH2, TC4_CH0, EXTERNAL_INT_6 },
  { PORTA, 23, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, TCC0_CH3, TC4_CH1, EXTERNAL_INT_7 },
  { PORTA, 24, PIO_COM, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },
  { PORTA, 25, PIO_COM, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },
  { PORTA, 27, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTB,  0, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_3 },
  { PORTB,  1, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_1 },   
  { PORTB,  2, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, TCC2_CH2,  NOT_ON_TIMER, EXTERNAL_INT_2 },    
  { PORTB,  3, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM,  NOT_ON_TIMER, EXTERNAL_INT_3 },  
  { PORTB,  4, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_4 },   
  { PORTB,  5, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTB,  6, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_2 },   
  { PORTB,  7, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTB,  8, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_8 },      
  { PORTB,  9, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_9 },   
  { PORTB, 10, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTB, 11, PIO_DIGITAL, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },   
  { PORTB, 12, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_12 },  
  { PORTB, 13, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_13 },  
  { PORTB, 14, PIO_DIGITAL, PIN_ATTR_PWM_G, No_ADC_Channel, TCC0_CH2, NOT_ON_TIMER, EXTERNAL_INT_15 },      
  { PORTB, 15, PIO_DIGITAL, PIN_ATTR_PWM_F, No_ADC_Channel, TCC4_CH0, TC5_CH0, EXTERNAL_INT_15 },           
  { PORTB, 16, PIO_DIGITAL, PIN_ATTR_PWM_G, No_ADC_Channel, TCC0_CH4, NOT_ON_TIMER, EXTERNAL_INT_0 },       
  { PORTB, 17, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },
  { PORTB, 22, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_6 },   
  { PORTB, 23, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_7 },   
  { PORTB, 30, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_14 },  
  { PORTB, 31, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_15 },  
  { NOT_A_PORT, PIN_NOT_A_PIN, PIO_NOT_A_PIN, PIN_ATTR_NONE, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },

} ;

const void* g_apTCInstances[TCC_INST_NUM+TC_INST_NUM]={ TCC0, TCC1, TCC2, TCC3, TCC4, TC0, TC1, TC2, TC3, TC4, TC5 } ;
const uint32_t GCLK_CLKCTRL_IDs[TCC_INST_NUM+TC_INST_NUM] = { TCC0_GCLK_ID, TCC1_GCLK_ID, TCC2_GCLK_ID, TCC3_GCLK_ID, TCC4_GCLK_ID, TC0_GCLK_ID, TC1_GCLK_ID, TC2_GCLK_ID, TC3_GCLK_ID, TC4_GCLK_ID, TC5_GCLK_ID } ;

SERCOM sercom0( SERCOM0 ) ;
SERCOM sercom1( SERCOM1 ) ;
SERCOM sercom2( SERCOM2 ) ;
SERCOM sercom3( SERCOM3 ) ;
SERCOM sercom4( SERCOM4 ) ;
SERCOM sercom5( SERCOM5 ) ;

Uart Serial1( &sercom4, PIN_SERIAL1_RX, PIN_SERIAL1_TX, PAD_SERIAL1_RX, PAD_SERIAL1_TX ) ;

void SERCOM4_0_Handler()
{
  Serial1.IrqHandler();
}
void SERCOM4_1_Handler()
{
  Serial1.IrqHandler();
}
void SERCOM4_2_Handler()
{
  Serial1.IrqHandler();
}
void SERCOM4_3_Handler()
{
  Serial1.IrqHandler();
}


Uart Serial2( &sercom3, PIN_SERIAL2_RX, PIN_SERIAL2_TX, PAD_SERIAL2_RX, PAD_SERIAL2_TX ) ;

void SERCOM3_0_Handler()
{
  Serial2.IrqHandler();
}
void SERCOM3_1_Handler()
{
  Serial2.IrqHandler();
}
void SERCOM3_2_Handler()
{
  Serial2.IrqHandler();
}
void SERCOM3_3_Handler()
{
  Serial2.IrqHandler();
}

Dimitree · May 29, 2024, 9:52am

after some experimenting, I discovered that it is not possible to use analogRead on pins (array positions) 2, 3, 4, 5. So I moved A5 from position 5 to position 50 (the end of the array) and now everything is fine. I'm wondering what is the reason for that..

MartinL · May 29, 2024, 11:12am

Hi @Dimitree

That's because in the variant.cpp file, it's customary to place the digital pins at the beginning of the g_aPinDescription[] array, where their position or index is equivalent to the digital pin number, for example D8 is at array location 8.

The analog pin numbers A0, A1, A2, etc... are mapped to the later g_aPinDescription[] indices using defines in the variant.h file.

system · November 25, 2024, 11:12am

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SAMD51: analogWrite on A5 not working after editing variant file

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