examples: Add ADC examples

Add ADC examples for all boards to demonstrate how to read from the
analog pins.

examples/arduino-leonardo/src/bin/leonardo-adc.rs

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+#![no_std]
+#![no_main]
+
+use arduino_hal::prelude::*;
+use panic_halt as _;
+
+use arduino_hal::adc;
+
+#[arduino_hal::entry]
+fn main() -> ! {
+    let dp = arduino_hal::Peripherals::take().unwrap();
+    let pins = arduino_hal::pins!(dp);
+    let mut serial = arduino_hal::default_serial!(dp, pins, 57600);
+
+    let mut adc = arduino_hal::Adc::new(dp.ADC, Default::default());
+
+    let (vbg, gnd, tmp) = (
+        adc.read_blocking(&adc::channel::Vbg),
+        adc.read_blocking(&adc::channel::Gnd),
+        adc.read_blocking(&adc::channel::Temperature),
+    );
+    ufmt::uwriteln!(&mut serial, "Vbandgap: {}", vbg).void_unwrap();
+    ufmt::uwriteln!(&mut serial, "Ground: {}", gnd).void_unwrap();
+    ufmt::uwriteln!(&mut serial, "Temperature: {}", tmp).void_unwrap();
+
+    let a0 = pins.a0.into_analog_input(&mut adc);
+    let a1 = pins.a1.into_analog_input(&mut adc);
+    let a2 = pins.a2.into_analog_input(&mut adc);
+    let a3 = pins.a3.into_analog_input(&mut adc);
+    let a4 = pins.a4.into_analog_input(&mut adc);
+    let a5 = pins.a5.into_analog_input(&mut adc);
+
+    loop {
+        let values = [
+            a0.analog_read(&mut adc),
+            a1.analog_read(&mut adc),
+            a2.analog_read(&mut adc),
+            a3.analog_read(&mut adc),
+            a4.analog_read(&mut adc),
+            a5.analog_read(&mut adc),
+        ];
+
+        for (i, v) in values.iter().enumerate() {
+            ufmt::uwrite!(&mut serial, "A{}: {} ", i, v).void_unwrap();
+        }
+
+        ufmt::uwriteln!(&mut serial, "").void_unwrap();
+        arduino_hal::delay_ms(1000);
+    }
+}

examples/arduino-mega2560/src/bin/mega2560-adc.rs

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+#![no_std]
+#![no_main]
+
+use arduino_hal::prelude::*;
+use panic_halt as _;
+
+use arduino_hal::adc;
+
+#[arduino_hal::entry]
+fn main() -> ! {
+    let dp = arduino_hal::Peripherals::take().unwrap();
+    let pins = arduino_hal::pins!(dp);
+    let mut serial = arduino_hal::default_serial!(dp, pins, 57600);
+
+    let mut adc = arduino_hal::Adc::new(dp.ADC, Default::default());
+
+    let (vbg, gnd) = (
+        adc.read_blocking(&adc::channel::Vbg),
+        adc.read_blocking(&adc::channel::Gnd),
+    );
+    ufmt::uwriteln!(&mut serial, "Vbandgap: {}", vbg).void_unwrap();
+    ufmt::uwriteln!(&mut serial, "Ground: {}", gnd).void_unwrap();
+
+    // To store multiple channels in an array, we use the `into_channel()` method.
+    let channels: [adc::Channel; 16] = [
+        pins.a0.into_analog_input(&mut adc).into_channel(),
+        pins.a1.into_analog_input(&mut adc).into_channel(),
+        pins.a2.into_analog_input(&mut adc).into_channel(),
+        pins.a3.into_analog_input(&mut adc).into_channel(),
+        pins.a4.into_analog_input(&mut adc).into_channel(),
+        pins.a5.into_analog_input(&mut adc).into_channel(),
+        pins.a6.into_analog_input(&mut adc).into_channel(),
+        pins.a7.into_analog_input(&mut adc).into_channel(),
+        pins.a8.into_analog_input(&mut adc).into_channel(),
+        pins.a9.into_analog_input(&mut adc).into_channel(),
+        pins.a10.into_analog_input(&mut adc).into_channel(),
+        pins.a11.into_analog_input(&mut adc).into_channel(),
+        pins.a12.into_analog_input(&mut adc).into_channel(),
+        pins.a13.into_analog_input(&mut adc).into_channel(),
+        pins.a14.into_analog_input(&mut adc).into_channel(),
+        pins.a15.into_analog_input(&mut adc).into_channel(),
+    ];
+
+    loop {
+        for (i, ch) in channels.iter().enumerate() {
+            let v = adc.read_blocking(ch);
+            ufmt::uwrite!(&mut serial, "A{}: {} ", i, v).void_unwrap();
+        }
+
+        ufmt::uwriteln!(&mut serial, "").void_unwrap();
+        arduino_hal::delay_ms(1000);
+    }
+}

examples/arduino-uno/src/bin/uno-adc.rs

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+#![no_std]
+#![no_main]
+
+use arduino_hal::prelude::*;
+use panic_halt as _;
+
+use arduino_hal::adc;
+
+#[arduino_hal::entry]
+fn main() -> ! {
+    let dp = arduino_hal::Peripherals::take().unwrap();
+    let pins = arduino_hal::pins!(dp);
+    let mut serial = arduino_hal::default_serial!(dp, pins, 57600);
+
+    let mut adc = arduino_hal::Adc::new(dp.ADC, Default::default());
+
+    let (vbg, gnd, tmp) = (
+        adc.read_blocking(&adc::channel::Vbg),
+        adc.read_blocking(&adc::channel::Gnd),
+        adc.read_blocking(&adc::channel::Temperature),
+    );
+    ufmt::uwriteln!(&mut serial, "Vbandgap: {}", vbg).void_unwrap();
+    ufmt::uwriteln!(&mut serial, "Ground: {}", gnd).void_unwrap();
+    ufmt::uwriteln!(&mut serial, "Temperature: {}", tmp).void_unwrap();
+
+    let a0 = pins.a0.into_analog_input(&mut adc);
+    let a1 = pins.a1.into_analog_input(&mut adc);
+    let a2 = pins.a2.into_analog_input(&mut adc);
+    let a3 = pins.a3.into_analog_input(&mut adc);
+    let a4 = pins.a4.into_analog_input(&mut adc);
+    let a5 = pins.a5.into_analog_input(&mut adc);
+
+    loop {
+        let values = [
+            a0.analog_read(&mut adc),
+            a1.analog_read(&mut adc),
+            a2.analog_read(&mut adc),
+            a3.analog_read(&mut adc),
+            a4.analog_read(&mut adc),
+            a5.analog_read(&mut adc),
+        ];
+
+        for (i, v) in values.iter().enumerate() {
+            ufmt::uwrite!(&mut serial, "A{}: {} ", i, v).void_unwrap();
+        }
+
+        // Arduino Nano has two more ADC pins A6 and A7.  Accessing them works a bit different from
+        // the other pins as they are not normal IO pins.  The code below shows how it works.
+        let (a6, a7) = (
+            adc.read_blocking(&channel::ADC6),
+            adc.read_blocking(&channel::ADC7),
+        );
+        ufmt::uwrite!(&mut serial, "A6: {} A7: {}", a6, a7).void_unwrap();
+
+        ufmt::uwriteln!(&mut serial, "").void_unwrap();
+        arduino_hal::delay_ms(1000);
+    }
+}