implement embedded-io v0.6 Read & Write

with `embedded-hal` v1 the USART traits have been removed in favour of the new `embedded-io` crate. this adds a (very basic) implementation for `Read` and `Write`. other traits (such as the `*Ready` or `BufRead` traits) have not (yet) been implemented and some (like `Seek`) probably can't be implemented for this HAL. a better implementation might use a buffer in the background to receive more than one byte at once. see also #249 for a related PR. this is part of #468
Rahix · Dec 28, 2023 · 3679a64 · 3679a64
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diff --git a/avr-hal-generic/Cargo.toml b/avr-hal-generic/Cargo.toml
@@ -12,6 +12,7 @@ paste = "1.0.0"
 avr-device = "0.5.3"
 embedded-storage = "0.2"
 embedded-hal = "1.0.0-rc.3"
+embedded-io = "0.6.1"
 
 [dependencies.embedded-hal-v0]
 version = "0.2.3"

diff --git a/avr-hal-generic/src/usart.rs b/avr-hal-generic/src/usart.rs
@@ -3,8 +3,11 @@
 //! Check the documentation of [`Usart`] for details.
 
 use core::cmp::Ordering;
+use core::convert::Infallible;
 use core::marker;
 
+use embedded_io::ErrorType;
+
 use crate::port;
 
 /// Representation of a USART baudrate
@@ -183,21 +186,21 @@ pub trait UsartOps<H, RX, TX> {
     /// was flushed yet.
     ///
     /// **Warning**: This is a low-level method and should not be called directly from user code.
-    fn raw_flush(&mut self) -> nb::Result<(), core::convert::Infallible>;
+    fn raw_flush(&mut self) -> nb::Result<(), Infallible>;
     /// Write a byte to the TX buffer.
     ///
     /// This operation must be non-blocking and return [`nb::Error::WouldBlock`] until the byte is
     /// enqueued.  The operation should not wait for the byte to have actually been sent.
     ///
     /// **Warning**: This is a low-level method and should not be called directly from user code.
-    fn raw_write(&mut self, byte: u8) -> nb::Result<(), core::convert::Infallible>;
+    fn raw_write(&mut self, byte: u8) -> nb::Result<(), Infallible>;
     /// Read a byte from the RX buffer.
     ///
     /// This operation must be non-blocking and return [`nb::Error::WouldBlock`] if no incoming
     /// byte is available.
     ///
     /// **Warning**: This is a low-level method and should not be called directly from user code.
-    fn raw_read(&mut self) -> nb::Result<u8, core::convert::Infallible>;
+    fn raw_read(&mut self) -> nb::Result<u8, Infallible>;
 
     /// Enable/Disable a certain interrupt.
     ///
@@ -335,7 +338,7 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> Usart<H, USART, RX, TX, CLOCK
 }
 
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ufmt::uWrite for Usart<H, USART, RX, TX, CLOCK> {
-    type Error = core::convert::Infallible;
+    type Error = Infallible;
 
     fn write_str(&mut self, s: &str) -> Result<(), Self::Error> {
         for b in s.as_bytes().iter() {
@@ -348,7 +351,7 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ufmt::uWrite for Usart<H, USA
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> hal::serial::Write<u8>
     for Usart<H, USART, RX, TX, CLOCK>
 {
-    type Error = core::convert::Infallible;
+    type Error = Infallible;
 
     fn write(&mut self, byte: u8) -> nb::Result<(), Self::Error> {
         self.p.raw_write(byte)
@@ -359,16 +362,78 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> hal::serial::Write<u8>
     }
 }
 
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ErrorType for Usart<H, USART, RX, TX, CLOCK> { type Error = Infallible; }
+
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> embedded_io::Write for Usart<H, USART, RX, TX, CLOCK> {
+    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
+        // block for first byte
+        self.write_byte(buf[0]);
+        let mut i = 1;
+
+        // write more bytes if it's possible
+        for byte in buf[1..].iter() {
+            match self.p.raw_write(*byte) {
+                Ok(_) => {
+                    i += 1;
+                }
+                Err(nb::Error::WouldBlock) => {
+                    return Ok(i);
+                }
+                Err(_) => {
+                    unreachable!(); // `raw_write` is `Infallible`
+                }
+            }
+        }
+        Ok(i)
+    }
+
+    fn flush(&mut self) -> Result<(), Self::Error> {
+        self.p.raw_flush().unwrap(); // `raw_write` is `Infallible`
+        Ok(())
+    }
+}
+
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> hal::serial::Read<u8>
     for Usart<H, USART, RX, TX, CLOCK>
 {
-    type Error = core::convert::Infallible;
+    type Error = Infallible;
 
     fn read(&mut self) -> nb::Result<u8, Self::Error> {
         self.p.raw_read()
     }
 }
 
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> embedded_io::Read for Usart<H, USART, RX, TX, CLOCK> {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
+        // block for first byte
+        buf[0] = self.read_byte();
+        let mut i = 1;
+
+        // grab more bytes if available
+        loop {
+            match self.p.raw_read() {
+                Ok(byte) => {
+                    buf[i] = byte;
+                    i += 1;
+
+                    if i == buf.len() {
+                        return Ok(i);
+                    }
+                }
+                Err(nb::Error::WouldBlock) => {
+                    return Ok(i);
+                }
+                Err(_) => {
+                    unreachable!(); // `raw_read` is `Infallible`
+                }
+            }
+        }
+    }
+}
+
 /// Writer half of a [`Usart`] peripheral.
 ///
 /// Created by calling [`Usart::split`].  Splitting a peripheral into reader and writer allows
@@ -412,6 +477,14 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> UsartWriter<H, USART, RX, TX,
             _h: marker::PhantomData,
         }
     }
+
+    /// Transmit a byte.
+    ///
+    /// This method will block until the byte has been enqueued for transmission but **not** until
+    /// it was entirely sent.
+    fn write_byte(&mut self, byte: u8) {
+        nb::block!(self.p.raw_write(byte)).unwrap()
+    }
 }
 
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> UsartReader<H, USART, RX, TX, CLOCK> {
@@ -433,7 +506,7 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> UsartReader<H, USART, RX, TX,
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ufmt::uWrite
     for UsartWriter<H, USART, RX, TX, CLOCK>
 {
-    type Error = core::convert::Infallible;
+    type Error = Infallible;
 
     fn write_str(&mut self, s: &str) -> Result<(), Self::Error> {
         for b in s.as_bytes().iter() {
@@ -446,7 +519,7 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ufmt::uWrite
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> hal::serial::Write<u8>
     for UsartWriter<H, USART, RX, TX, CLOCK>
 {
-    type Error = core::convert::Infallible;
+    type Error = Infallible;
 
     fn write(&mut self, byte: u8) -> nb::Result<(), Self::Error> {
         self.p.raw_write(byte)
@@ -457,16 +530,77 @@ impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> hal::serial::Write<u8>
     }
 }
 
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ErrorType for UsartWriter<H, USART, RX, TX, CLOCK> { type Error = Infallible; }
+
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> embedded_io::Write for UsartWriter<H, USART, RX, TX, CLOCK> {
+    fn write(&mut self, buf: &[u8]) -> Result<usize, Self::Error> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
+        // block for first byte
+        self.write_byte(buf[0]);
+        let mut i = 1;
+
+        // write more bytes if it's possible
+        for byte in buf[1..].iter() {
+            match self.p.raw_write(*byte) {
+                Ok(_) => {
+                    i += 1;
+                }
+                Err(nb::Error::WouldBlock) => {
+                    return Ok(i);
+                }
+                Err(_) => {
+                    unreachable!(); // `raw_write` is `Infallible`
+                }
+            }
+        }
+        Ok(i)
+    }
+
+    fn flush(&mut self) -> Result<(), Self::Error> {
+        self.p.raw_flush().unwrap(); // `raw_flush` is `Infallible`
+        Ok(())
+    }
+}
+
 impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> hal::serial::Read<u8>
     for UsartReader<H, USART, RX, TX, CLOCK>
 {
-    type Error = core::convert::Infallible;
+    type Error = Infallible;
 
     fn read(&mut self) -> nb::Result<u8, Self::Error> {
         self.p.raw_read()
     }
 }
 
+
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> ErrorType for UsartReader<H, USART, RX, TX, CLOCK> { type Error = Infallible; }
+
+impl<H, USART: UsartOps<H, RX, TX>, RX, TX, CLOCK> embedded_io::Read for UsartReader<H, USART, RX, TX, CLOCK> {
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
+        let mut i = 0;
+        loop {
+            match self.p.raw_read() {
+                Ok(byte) => {
+                    buf[i] = byte;
+                    i += 1;
+
+                    if i == buf.len() {
+                        return Ok(i);
+                    }
+                }
+                Err(nb::Error::WouldBlock) => {
+                    return Ok(i);
+                }
+                Err(_) => {
+                    unreachable!(); // `raw_read` is `Infallible`
+                }
+            }
+        }
+    }
+}
+
 #[macro_export]
 macro_rules! impl_usart_traditional {
     (

diff --git a/examples/arduino-uno/Cargo.toml b/examples/arduino-uno/Cargo.toml
@@ -13,6 +13,7 @@ embedded-hal = "1.0.0-rc.3"
 pwm-pca9685 = "0.3.1"
 infrared = "0.14.1"
 embedded-storage = "0.2"
+embedded-io = "0.6.1"
 
 [dependencies.embedded-hal-v0]
 version = "0.2.3"

diff --git a/examples/arduino-uno/src/bin/uno-usart-embedded-io.rs b/examples/arduino-uno/src/bin/uno-usart-embedded-io.rs
@@ -0,0 +1,29 @@
+/*!
+ * Demonstration of writing to and reading from the serial console.
+ */
+#![no_std]
+#![no_main]
+
+use panic_halt as _;
+
+use embedded_io::{Read, Write};
+
+fn usart_handler(serial: &mut (impl Read + Write)) -> ! {
+    serial.write_all("Hello from Arduino!\r\n".as_bytes()).unwrap();
+
+    loop {
+        let mut rx_buf: [u8; 16] = [0; 16];
+        let len = serial.read(&mut rx_buf).unwrap();
+
+        writeln!(serial, "Got {:?} (which is {} bytes long)", &rx_buf[..len], len).unwrap();
+    }
+}
+
+#[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);
+
+    usart_handler(&mut serial);
+}