Documentation of pinouts is unclear

[leekillough]

1. I am confused on Page 21 of the manual, where it implies there are extra "Analog, PWM, GPIO" pins on the expansion header. Are they the ones labeled EXT_PA21, EXT_PA22, EXT_PA23? Can they each be programmed as either Analog IN, Digital IN, Digital OUT, Open Collector, or PWM, or are they limited to digital in/out?
2. What Is EXT_NS0? Is it a digital output which can be used to select a SPI slave device, as well as a possibly independent digital output if you don't need to select between multiple SPI devices?
3. How many, if any, of the CAN, I2C, SPI, and serial (RX/TX + RX2/TX2) pins can be reprogrammed for other functions, and to what degree (analog, digital IN/OUT/OC, PWM)?
4. Is EXT_SCK the SPI sclock, and is EXT_SCL the I2C sclock? I wanted to make sure, since I2C and SPI were not mentioned in detail in the manual. Perhaps sections on I2C and SPI, with simple circuit examples, should be added.

[ppescher]

The design of OpenTracker 2 is derived from Arduino Due and tries to be as much software compatible as possible. Some pins are configured the same way, some are different. Please have a look at: https://github.com/geolink/opentracker-arduino-board/blob/master/1.0.2/variants/geolink_opentracker/variant.h and CPP file, where you can see what function is the default one for each pin.

To answer your questions:

1. Usually all the pins can function as digital I/O, some have PWM capability, some can be analog inputs. See OpenTracker "variant.h/.cpp"
2. NS0 is standard naming for Atmel SAM3 MCU. It is a "slave select" or "chip select" pin for the SPI.
3. Again, please look at "variant.h/.cpp" and refer to the SAM3AC4 datasheet for multiplexed pin functions. The only analog pins in the expansion header are PA22/PA23 (you can use AIN_pin_name definitions for analog functions) and PA21 can be a PWM output.
4. SCK is the SPI serial clock. SCL is the I2C serial clock. This is common naming, but thanks for your comments. We'll try to improve the manual.