ATSAMD21J Test

Posted on by Pipkins, Royce

Recently Arduino came out with the Arduino Zero. This is a neat 48MHz ARM Cortex M0 processor on a PCB with the same pin outs as an Arduino UNO. Existing 3rd party UNO libraries are a little hit and miss because some access the underlying hardware registers of the UNO. The Zero hardware registers are completely different from UNO. Still, the basic 1st party Arduino libraries work fine and I’m sure those 3rd party libraries that were twiddling the UNO hardware registers directly will start to support the Zero over time.

Anway, my curiosity was peaked by the ARM processor for the Zero the Atmel ATSAMD21G18. It turns out that the processor has alternative packages with higher pin counts. Same silicon, just more pins. So I gave the ATSAMD21J18 a try. In order to be able to use extra pins with digitalWrite, I had to add a small amount of code to a file called variant.cpp, but once done, I had a Zero with a nice chunk of extra I/O capability.

Here are my variant.cpp additions, tacked on to the definition of g_APinDescription:

 //Extra J pins
 { PORTB, 4, PIO_DIGITAL, PIN_ATTR_ANALOG, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 5, PIO_DIGITAL, PIN_ATTR_ANALOG, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 6, PIO_DIGITAL, PIN_ATTR_ANALOG, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 7, PIO_DIGITAL, PIN_ATTR_ANALOG, 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_NONE }, 
 { PORTB, 13, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 14, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 15, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 
 { PORTB, 16, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 17, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 
 { PORTB, 30, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE }, 
 { PORTB, 31, PIO_DIGITAL, PIN_ATTR_DIGITAL, 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_NONE }, 
 { PORTB, 1, PIO_DIGITAL, PIN_ATTR_DIGITAL, No_ADC_Channel, NOT_ON_PWM, NOT_ON_TIMER, EXTERNAL_INT_NONE },

Right now this is digital only. Some addition modifications to other files would be needed to pick up analog or pwm.