Merge pull request #3347 from kalkyl/pio-onewire

rp: Add PIO example for one-wire temperature sensor

1 files changed, 155 insertions, 0 deletions

diff --git a/examples/rp/src/bin/pio_onewire.rs b/examples/rp/src/bin/pio_onewire.rs
new file mode 100644
index 000000000..5076101ec
--- /dev/null
+++ b/examples/rp/src/bin/pio_onewire.rs
@@ -0,0 +1,155 @@
+//! This example shows how you can use PIO to read a `DS18B20` one-wire temperature sensor.
+
+#![no_std]
+#![no_main]
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_rp::bind_interrupts;
+use embassy_rp::peripherals::PIO0;
+use embassy_rp::pio::{self, Common, Config, InterruptHandler, Pio, PioPin, ShiftConfig, ShiftDirection, StateMachine};
+use embassy_time::Timer;
+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 mut sensor = Ds18b20::new(&mut pio.common, pio.sm0, p.PIN_2);
+
+    loop {
+        sensor.start().await; // Start a new measurement
+        Timer::after_secs(1).await; // Allow 1s for the measurement to finish
+        match sensor.temperature().await {
+            Ok(temp) => info!("temp = {:?} deg C", temp),
+            _ => error!("sensor error"),
+        }
+        Timer::after_secs(1).await;
+    }
+}
+
+/// DS18B20 temperature sensor driver
+pub struct Ds18b20<'d, PIO: pio::Instance, const SM: usize> {
+    sm: StateMachine<'d, PIO, SM>,
+}
+
+impl<'d, PIO: pio::Instance, const SM: usize> Ds18b20<'d, PIO, SM> {
+    /// Create a new instance the driver
+    pub fn new(common: &mut Common<'d, PIO>, mut sm: StateMachine<'d, PIO, SM>, pin: impl PioPin) -> Self {
+        let prg = pio_proc::pio_asm!(
+            r#"
+                .wrap_target
+                    again:
+                        pull block
+                        mov x, osr
+                        jmp !x, read
+                        write:
+                            set pindirs, 1 
+                            set pins, 0  
+                            loop1: 
+                                jmp x--,loop1
+                            set pindirs, 0 [31]
+                            wait 1 pin 0 [31]
+                            pull block
+                            mov x, osr
+                            bytes1:
+                                pull block
+                                set y, 7    
+                                set pindirs, 1 
+                                bit1:
+                                    set pins, 0 [1]
+                                    out pins,1 [31]
+                                    set pins, 1 [20]
+                                    jmp y--,bit1
+                                jmp x--,bytes1
+                            set pindirs, 0 [31]
+                            jmp again
+                        read:
+                            pull block
+                            mov x, osr
+                            bytes2:
+                                set y, 7
+                                bit2:
+                                    set pindirs, 1 
+                                    set pins, 0 [1]  
+                                    set pindirs, 0 [5]
+                                    in pins,1 [10]   
+                                    jmp y--,bit2
+                            jmp x--,bytes2
+                .wrap
+            "#,
+        );
+
+        let pin = common.make_pio_pin(pin);
+        let mut cfg = Config::default();
+        cfg.use_program(&common.load_program(&prg.program), &[]);
+        cfg.set_out_pins(&[&pin]);
+        cfg.set_in_pins(&[&pin]);
+        cfg.set_set_pins(&[&pin]);
+        cfg.shift_in = ShiftConfig {
+            auto_fill: true,
+            direction: ShiftDirection::Right,
+            threshold: 8,
+        };
+        cfg.clock_divider = 255_u8.into();
+        sm.set_config(&cfg);
+        sm.set_enable(true);
+        Self { sm }
+    }
+
+    /// Write bytes over the wire
+    async fn write_bytes(&mut self, bytes: &[u8]) {
+        self.sm.tx().wait_push(250).await;
+        self.sm.tx().wait_push(bytes.len() as u32 - 1).await;
+        for b in bytes {
+            self.sm.tx().wait_push(*b as u32).await;
+        }
+    }
+
+    /// Read bytes from the wire
+    async fn read_bytes(&mut self, bytes: &mut [u8]) {
+        self.sm.tx().wait_push(0).await;
+        self.sm.tx().wait_push(bytes.len() as u32 - 1).await;
+        for b in bytes.iter_mut() {
+            *b = (self.sm.rx().wait_pull().await >> 24) as u8;
+        }
+    }
+
+    /// Calculate CRC8 of the data
+    fn crc8(data: &[u8]) -> u8 {
+        let mut temp;
+        let mut data_byte;
+        let mut crc = 0;
+        for b in data {
+            data_byte = *b;
+            for _ in 0..8 {
+                temp = (crc ^ data_byte) & 0x01;
+                crc >>= 1;
+                if temp != 0 {
+                    crc ^= 0x8C;
+                }
+                data_byte >>= 1;
+            }
+        }
+        crc
+    }
+
+    /// Start a new measurement. Allow at least 1000ms before getting `temperature`.
+    pub async fn start(&mut self) {
+        self.write_bytes(&[0xCC, 0x44]).await;
+    }
+
+    /// Read the temperature. Ensure >1000ms has passed since `start` before calling this.
+    pub async fn temperature(&mut self) -> Result<f32, ()> {
+        self.write_bytes(&[0xCC, 0xBE]).await;
+        let mut data = [0; 9];
+        self.read_bytes(&mut data).await;
+        match Self::crc8(&data) == 0 {
+            true => Ok(((data[1] as u32) << 8 | data[0] as u32) as f32 / 16.),
+            false => Err(()),
+        }
+    }
+}