2 files changed, 90 insertions, 0 deletions

diff --git a/examples/rp/src/bin/pio_onewire.rs b/examples/rp/src/bin/pio_onewire.rs
index 379e2b8f9..102f13c45 100644
--- a/examples/rp/src/bin/pio_onewire.rs
+++ b/examples/rp/src/bin/pio_onewire.rs
@@ -1,4 +1,5 @@
 //! This example shows how you can use PIO to read one or more `DS18B20` one-wire temperature sensors.
+//! This uses externally powered sensors. For parasite power, see the pio_onewire_parasite.rs example.
 
 #![no_std]
 #![no_main]
diff --git a/examples/rp/src/bin/pio_onewire_parasite.rs b/examples/rp/src/bin/pio_onewire_parasite.rs
new file mode 100644
index 000000000..fd076dee0
--- /dev/null
+++ b/examples/rp/src/bin/pio_onewire_parasite.rs
@@ -0,0 +1,89 @@
+//! This example shows how you can use PIO to read one or more `DS18B20`
+//! one-wire temperature sensors using parasite power.
+//! It applies a strong pullup during conversion, see "Powering the DS18B20" in the datasheet.
+//! For externally powered sensors, use the pio_onewire.rs example.
+
+#![no_std]
+#![no_main]
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_rp::bind_interrupts;
+use embassy_rp::peripherals::PIO0;
+use embassy_rp::pio::{InterruptHandler, Pio};
+use embassy_rp::pio_programs::onewire::{PioOneWire, PioOneWireProgram, PioOneWireSearch};
+use embassy_time::Duration;
+use heapless::Vec;
+use {defmt_rtt as _, panic_probe as _};
+
+bind_interrupts!(struct Irqs {
+    PIO0_IRQ_0 => InterruptHandler<PIO0>;
+});
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_rp::init(Default::default());
+    let mut pio = Pio::new(p.PIO0, Irqs);
+
+    let prg = PioOneWireProgram::new(&mut pio.common);
+    let mut onewire = PioOneWire::new(&mut pio.common, pio.sm0, p.PIN_2, &prg);
+
+    info!("Starting onewire search");
+
+    let mut devices = Vec::<u64, 10>::new();
+    let mut search = PioOneWireSearch::new();
+    for _ in 0..10 {
+        if !search.is_finished() {
+            if let Some(address) = search.next(&mut onewire).await {
+                if crc8(&address.to_le_bytes()) == 0 {
+                    info!("Found address: {:x}", address);
+                    let _ = devices.push(address);
+                } else {
+                    warn!("Found invalid address: {:x}", address);
+                }
+            }
+        }
+    }
+
+    info!("Search done, found {} devices", devices.len());
+
+    loop {
+        // Read all devices one by one
+        for device in &devices {
+            onewire.reset().await;
+            onewire.write_bytes(&[0x55]).await; // Match rom
+            onewire.write_bytes(&device.to_le_bytes()).await;
+            // 750 ms delay required for default 12-bit resolution.
+            onewire.write_bytes_pullup(&[0x44], Duration::from_millis(750)).await;
+
+            onewire.reset().await;
+            onewire.write_bytes(&[0x55]).await; // Match rom
+            onewire.write_bytes(&device.to_le_bytes()).await;
+            onewire.write_bytes(&[0xBE]).await; // Read scratchpad
+
+            let mut data = [0; 9];
+            onewire.read_bytes(&mut data).await;
+            if crc8(&data) == 0 {
+                let temp = ((data[1] as u32) << 8 | data[0] as u32) as f32 / 16.;
+                info!("Read device {:x}: {} deg C", device, temp);
+            } else {
+                warn!("Reading device {:x} failed. {:02x}", device, data);
+            }
+        }
+    }
+}
+
+fn crc8(data: &[u8]) -> u8 {
+    let mut crc = 0;
+    for b in data {
+        let mut data_byte = *b;
+        for _ in 0..8 {
+            let temp = (crc ^ data_byte) & 0x01;
+            crc >>= 1;
+            if temp != 0 {
+                crc ^= 0x8C;
+            }
+            data_byte >>= 1;
+        }
+    }
+    crc
+}