Add example for sigma-delta modulation

Issue esp-rs#2370

Author: katyo

examples/src/bin/sdm.rs

@@ -0,0 +1,52 @@
+//! Connect an oscilloscope to an IO pin and see the modulation sine wave.
+//!
+//! Also you may connect low-pass filter to SDM output.
+//!
+//! The following wiring is assumed for ESP32:
+//! - SDM pin => GPIO32
+//! The following wiring is assumed for ESP32S2/S3:
+//! - SDM pin => GPIO3
+//! The following wiring is assumed for others:
+//! - SDM pin => GPIO2
+
+//% CHIPS: esp32 esp32c3 esp32c6 esp32h2 esp32s2 esp32s3
+
+#![no_std]
+#![no_main]
+
+use esp_backtrace as _;
+use esp_hal::{
+    sdm::Sdm,
+    delay::Delay,
+    gpio::Io,
+    prelude::*,
+};
+use esp_println::println;
+
+#[entry]
+fn main() -> ! {
+    let peripherals = esp_hal::init(esp_hal::Config::default());
+
+    let io = Io::new(peripherals.GPIO, peripherals.IO_MUX);
+    cfg_if::cfg_if! {
+        if #[cfg(feature = "esp32")] {
+            let modulation_pin = io.pins.gpio32;
+        } else if #[cfg(any(feature = "esp32s2", feature = "esp32s3"))] {
+            let modulation_pin = io.pins.gpio3;
+        } else {
+            let modulation_pin = io.pins.gpio2;
+        }
+    }
+
+    let mut sdm = Sdm::new(peripherals.GPIO_SD);
+    let mut sdm_ch = sdm.enable_pin(modulation_pin, 100.kHz()).unwrap();
+
+    let delay = Delay::new();
+
+    println!("Sigma-delta modulation is on");
+
+    loop {
+        sdm_ch.set_pulse_density(0);
+        delay.delay_millis(1500);
+    }
+}