Generate a user-readable report of the current state of the pins (what they're doing) on Arduino Zero and other SAMD21 based systems
In the forum discussion here: http://forum.arduino.cc/index.php?topic=403674.msg2776323 the question is asked
"How can I tell how the Arduino core has configured the various multi-purpose pins of the SAMD21 chip?"
This is a good question, and one that CAN be answered without too much trouble, since the SAMD21 controls the pins from a central "Pin Multiplexing" datastructure. Each pin has a bit saying whether it is just GPIO or "something else", and a separate field describing the "something else." It's just a SMOP to decode this information. (and invitingly, while a full decode is possible, even a relatively minor effort can yield useful information.)
Sample Output
SAMD Pin State Report
0 PA11 PMUX(2) SERCOM0 P3(UART)
1 PA10 PMUX(2) SERCOM0 P2(UART)
2 PA14 GPIO I
3 PA09 GPIO I
4 PA08 GPIO I
5 PA15 GPIO I
6 PA20 GPIO I
7 PA21 GPIO I
8 PA06 GPIO I
9 PA07 GPIO I
10 PA18 PMUX(4) TC3/WO0
11 PA16 GPIO I
12 PA19 PMUX(5) TCC0/WO3
13 PA17 GPIO O
14 (A0) PA02 PMUX(1) ADC
15 (A1) PB08 PMUX(1) ADC
16 (A2) PB09 PMUX(1) ADC
17 (A3) PA04 PMUX(1) ADC
18 (A4) PA05 PMUX(1) ADC
19 (A5) PB02 PMUX(1) ADC
20 PA22 PMUX(2) SERCOM3 P0(I2C Master)
21 PA23 PMUX(2) SERCOM3 P1(I2C Master)
22 PA12 PMUX(3) SERCOM4 P0(SPI Master)
23 PB10 PMUX(3) SERCOM4 P2(SPI Master)
24 PB11 PMUX(3) SERCOM4 P3(SPI Master)
25 PB03 GPIO I
26 PA27 GPIO I
27 PA28 GPIO I
28 PA24 PMUX(6) COM(USB)
29 PA25 PMUX(6) COM(USB)
30 PB22 PMUX(3) SERCOM5 P2(UART)
31 PB23 PMUX(3) SERCOM5 P3(UART)
32 PA22 PMUX(2) SERCOM3 P0(I2C Master)
33 PA23 PMUX(2) SERCOM3 P1(I2C Master)
34 PA19 PMUX(5) TCC0/WO3
35 PA16 GPIO I
36 PA18 PMUX(4) TC3/WO0
37 PA17 GPIO O
38 PA13 GPIO I
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