How do I read multiple ADC channels from a SAMD21 configured in atmel.start?

Question

I'm stuck with trying to read multiple ADC channels on a SAMD21 that I have configured using ATMEL.start. I am very new to Microchip Studio (Arduino convert trying to upgrade).

The below code is my basic "read the input voltage" function to test the ADC. My issue is that I have tried changing the channel number (0 below) to both the sequential channels set in Atmel Start ADC confuration (i.e. 0 is PA08/AIN16, 1 is PA09/AIN17, etc.), and the absolute AIN channel, i.e. 16, 17, 18, ...

This gives me exactly the same result for each channel, and not different results for the 4 pins. I have tried enabling the channel before reading each one (no joy) and I have tried using the adc_sync_set_inputs with odd results.

Can somebody give me an example of how to read two ADC inputs, on pins PA08 and PA09, please? I have been banging my head on datasheets and tutorials for days!

Code and atmel.start configuration below:

[![atmel start adc setting][1]][1]

static void read_battery_level()
{
    adc_sync_enable_channel(&ADC_BATTERY, 0); // enable ADC, channel 0
    
    uint32_t sum = 0;
    for (int i=0; i<NUM_READINGS; i++)
    {
        // read from ADC channel 0
        adc_sync_read_channel(&ADC_BATTERY, 0, battery_reading.c, 2); // 0 is the channel, the .c is the union variable (like a struct)
        
        //add to sum
        sum += battery_reading.i;
        
        //short delay
        delay_us(20);
    }
    //calculate battery voltage
    battery_voltage = ((sum/NUM_READINGS) * ADC_LSB_MV) / 1000.0f;
}

Answer 1

It appears that channel is NOT implemented in the SAMD21 in Microchip Studio! Seems a little silly that all the tutorials mention the channel concept but it doesn't work. The following is a tested and working solution and works to change the input pin on the samd21:

uint8_t buffer[2];
 
adc_sync_set_inputs(&ADC,0x10,0x18,0); // set input pin: ADC, Positive pin, Negative pin, Channel (does nothing).
adc_sync_read_channel(&ADC_BATTERY, 0, buffer, 2);
 
uint16_t reading = (buffer[1] << 8) | buffer[0];
printf("Reading: %d ",reading);

Positive and negative pin values can be found in the hpl_adc_config.h file in the config folder.

For the negative pin, 0x18 is internal ground, 0x19 is I/O ground

For the positive pin, 0x00 = AIN0 ... 0x13=AIN19

I also found that pin defines didn't work (such as ADC_INPUTCTRL_MUXPOS_AIN1_Val) but the hex values did.

Thanks to all comments, much appreciated.