Rework reset_single_transaction feature to handle the reset correctly

If the feature is used, the reset needs to be added to the data before
sending it out. Otherwise, the reset is sent after the data is sent.

Also
- Always add mosi_idle_high reset to buffer
- Update comments
- Avoid constructing an additional array just to add the zeroes (will
probably result in the same binary)

Author: david-sawatzke

src/prerendered.rs

@@ -44,16 +44,19 @@ impl<'a, SPI, E> Ws2812<'a, SPI>
 where
     SPI: SpiBus<u8, Error = E>,
 {
-    /// Use ws2812 devices via spi
+    /// Use WS2812 devices via SPI
     ///
     /// The SPI bus should run within 2 MHz to 3.8 MHz
     ///
-    /// You may need to look at the datasheet and your own hal to verify this.
+    /// You may need to look at the datasheet and your own HAL to verify this.
     ///
-    /// You need to provide a buffer `data`, whoose length is at least 12 * the
-    /// length of the led strip + 140 bytes (or 280, if using the `mosi_idle_high` feature)
+    /// You need to provide a buffer `data`, whose length is at least 12 * the
+    /// length of the led strip
+    /// - + 140 bytes if using the `reset_single_transaction` feature
+    /// - + 140 bytes if using the `mosi_idle_high` feature
+    /// - + 280 bytes if using the `mosi_idle_high` and `reset_single_transaction` features
     ///
-    /// Please ensure that the mcu is pretty fast, otherwise weird timing
+    /// Please ensure that the MCU is pretty fast, otherwise weird timing
     /// issues will occur
     pub fn new(spi: SPI, data: &'a mut [u8]) -> Self {
         Self {
@@ -69,18 +72,21 @@ impl<'a, SPI, E> Ws2812<'a, SPI, devices::Sk6812w>
 where
     SPI: SpiBus<u8, Error = E>,
 {
-    /// Use sk6812w devices via spi
+    /// Use SK6812W devices via SPI
     ///
     /// The SPI bus should run within 2.3 MHz to 3.8 MHz at least.
     ///
-    /// You may need to look at the datasheet and your own hal to verify this.
+    /// You may need to look at the datasheet and your own HAL to verify this.
     ///
-    /// You need to provide a buffer `data`, whoose length is at least 16 * the
-    /// length of the led strip + 140 bytes (or 280, if using the `mosi_idle_high` feature)
+    /// You need to provide a buffer `data`, whose length is at least 16 * the
+    /// length of the led strip
+    /// - + 140 bytes if using the `reset_single_transaction` feature
+    /// - + 140 bytes if using the `mosi_idle_high` feature
+    /// - + 280 bytes if using the `mosi_idle_high` and `reset_single_transaction` features
     ///
-    /// Please ensure that the mcu is pretty fast, otherwise weird timing
+    /// Please ensure that the MCU is pretty fast, otherwise weird timing
     /// issues will occur
-    // The spi frequencies are just the limits, the available timing data isn't
+    // The SPI frequencies are just the limits, the available timing data isn't
     // complete
     pub fn new_sk6812w(spi: SPI, data: &'a mut [u8]) -> Self {
         Self {
@@ -96,7 +102,7 @@ impl<'a, SPI, D, E> Ws2812<'a, SPI, D>
 where
     SPI: SpiBus<u8, Error = E>,
 {
-    /// Write a single byte for ws2812 devices
+    /// Write a single byte for WS2812-like devices
     fn write_byte(&mut self, mut data: u8) -> Result<(), Error<E>> {
         // Send two bits in one spi byte. High time first, then the low time
         // The maximum for T0H is 500ns, the minimum for one bit 1063 ns.
@@ -116,21 +122,20 @@ where
     }
 
     /// Add a reset sequence (140 zeroes) to the data buffer
-    #[cfg(feature = "reset_single_transaction")]
-    fn flush(&mut self) -> Result<(), Error<E>> {
-        let flush_data = [(); FLUSH_DATA_LEN].map(|_| 0);
-
+    // Is always used for `mosi_idle_high`, as otherwise the time required to fill the buffer can lead to idle cycles on the SPI bus
+    fn write_reset(&mut self) -> Result<(), Error<E>> {
         if self.index + FLUSH_DATA_LEN > self.data.len() {
             return Err(Error::OutOfBounds);
         }
-        self.data[self.index..(self.index + FLUSH_DATA_LEN)].copy_from_slice(&flush_data);
-        self.index += FLUSH_DATA_LEN;
+        for _ in 0..FLUSH_DATA_LEN {
+            self.data[self.index] = 0;
+            self.index += 1;
+        }
         Ok(())
     }
 
     /// Send a reset sequence (140 zeroes) on the bus
-    #[cfg(not(feature = "reset_single_transaction"))]
-    fn flush(&mut self) -> Result<(), Error<E>> {
+    fn send_reset(&mut self) -> Result<(), Error<E>> {
         for _ in 0..FLUSH_DATA_LEN {
             self.spi.write(&[0]).map_err(Error::Spi)?;
         }
@@ -149,7 +154,7 @@ where
 {
     type Error = Error<E>;
     type Color = RGB8;
-    /// Write all the items of an iterator to a ws2812 strip
+    /// Write all the items of an iterator to a WS2812 strip
     fn write<T, I>(&mut self, iterator: T) -> Result<(), Error<E>>
     where
         T: IntoIterator<Item = I>,
@@ -158,7 +163,7 @@ where
         self.index = 0;
 
         if cfg!(feature = "mosi_idle_high") {
-            self.flush()?;
+            self.write_reset()?;
         }
 
         for item in iterator {
@@ -168,8 +173,16 @@ where
             self.write_byte(item.b)?;
         }
 
-        self.flush()?;
-        self.send_data().map_err(Error::Spi)
+        if cfg!(feature = "reset_single_transaction") {
+            self.write_reset()?;
+        }
+
+        self.send_data().map_err(Error::Spi)?;
+
+        if !cfg!(feature = "reset_single_transaction") {
+            self.send_reset()?;
+        }
+        Ok(())
     }
 }
 
@@ -179,7 +192,7 @@ where
 {
     type Error = Error<E>;
     type Color = RGBW<u8, u8>;
-    /// Write all the items of an iterator to a ws2812 strip
+    /// Write all the items of an iterator to a SK6812W strip
     fn write<T, I>(&mut self, iterator: T) -> Result<(), Error<E>>
     where
         T: IntoIterator<Item = I>,
@@ -188,7 +201,7 @@ where
         self.index = 0;
 
         if cfg!(feature = "mosi_idle_high") {
-            self.flush()?;
+            self.write_reset()?;
         }
 
         for item in iterator {
@@ -199,7 +212,15 @@ where
             self.write_byte(item.a.0)?;
         }
 
-        self.flush()?;
-        self.send_data().map_err(Error::Spi)
+        if cfg!(feature = "reset_single_transaction") {
+            self.write_reset()?;
+        }
+
+        self.send_data().map_err(Error::Spi)?;
+
+        if !cfg!(feature = "reset_single_transaction") {
+            self.send_reset()?;
+        }
+        Ok(())
     }
 }