examples: uno: Forward port the HC-SR04 example

examples/arduino-uno/src/bin/uno-hc-sr04.rs

@@ -0,0 +1,73 @@
+//! Example for using the HC-SR04 ultrasonic distance sensor
+//!
+//! Sensor Datasheet: https://www.electroschematics.com/hc-sr04-datasheet/
+//!
+//! Connections:
+//!   - TRIG <- D2
+//!   - ECHO -> D3
+#![no_std]
+#![no_main]
+
+use arduino_hal::prelude::*;
+use panic_halt as _;
+
+#[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 trig = pins.d2.into_output();
+    let echo = pins.d3;  // pin is input by default
+
+    // Starting and initializing the timer with prescaling 64.
+    // it gives one clock count every 4 µs.
+    // since the clock register size is 16 bits, the timer is full every
+    // 1/(16e6/64)*2^16 ≈ 260 ms
+    let timer1 = dp.TC1;
+    timer1.tccr1b.write(|w| w.cs1().prescale_64());
+
+    'outer: loop {
+        // the timer is reinitialized with value 0.
+        timer1.tcnt1.write(|w| unsafe { w.bits(0) });
+
+        // the trigger must be set to high under 10 µs as per the HC-SR04 datasheet
+        trig.set_high();
+        arduino_hal::delay_us(10);
+        trig.set_low();
+
+        while echo.is_low() {
+            // exiting the loop if the timer has reached 200 ms.
+            // 0.2s/4µs = 50000
+            if timer1.tcnt1.read().bits() >= 50000 {
+                // jump to the beginning of the outer loop if no obstacle is detected
+                ufmt::uwriteln!(
+                    &mut serial,
+                    "Nothing was detected and jump to outer loop.\r"
+                )
+                .void_unwrap();
+                continue 'outer;
+            }
+        }
+        // Restarting the timer
+        timer1.tcnt1.write(|w| unsafe { w.bits(0) });
+
+        // Wait for the echo to get low again
+        while echo.is_high() {}
+
+        // 1 count == 4 us, so the value is multiplied by 4.
+        // 1/58 ≈ (34000 ms/2)* 1µs
+        let value = (timer1.tcnt1.read().bits() * 4) / 58;
+
+        // Await 100 ms before sending the next trig
+        // 0.1s/4µs = 50000
+        while timer1.tcnt1.read().bits() < 25000 {}
+
+        ufmt::uwriteln!(
+            &mut serial,
+            "Hello, we are {} cms away from target!\r",
+            value
+        )
+        .void_unwrap();
+    }
+}