Merge #1345

1345: Added a neopixel constructor to spi, with an example in the stm32g0 d… r=Dirbaio a=smeenka

For Spi I added the possibility to use the Spi device as a Neopixel driver, with very precise timing, and not dependent on software during the transfer. Even without the --release flag, the timing is perfect.
Note that between the bursts of data the Mosi line should stay on low level. A resistor of 10k can guarantee that, as it seems the the pin is floating between the bursts (on the nucleo-G070RB platform I use).
I created an example for the STM32G0 family.
This example  does contain a very simple Neopixel driver, only for one type. But this Neopixel driver can easy be adapted to different types (for example RGBW types).


Co-authored-by: Dario Nieuwenhuis <dirbaio@dirbaio.net>
Co-authored-by: anton smeenk <asmeenk@planet.nl>

embassy-stm32/src/dma/bdma.rs

@@ -9,7 +9,8 @@ use embassy_cortex_m::interrupt::Priority;
 use embassy_hal_common::{into_ref, Peripheral, PeripheralRef};
 use embassy_sync::waitqueue::AtomicWaker;
 
-use super::{Dir, Word, WordSize};
+use super::word::{Word, WordSize};
+use super::Dir;
 use crate::_generated::BDMA_CHANNEL_COUNT;
 use crate::interrupt::{Interrupt, InterruptExt};
 use crate::pac;
@@ -167,7 +168,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             ptr as *mut u32,
             len,
             true,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -202,7 +203,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             ptr as *mut u32,
             len,
             true,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -225,7 +226,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             repeated as *const W as *mut u32,
             count,
             false,
-            W::bits(),
+            W::size(),
             options,
         )
     }

embassy-stm32/src/dma/dma.rs

@@ -9,7 +9,8 @@ use embassy_hal_common::{into_ref, Peripheral, PeripheralRef};
 use embassy_sync::waitqueue::AtomicWaker;
 use pac::dma::regs;
 
-use super::{Dir, Word, WordSize};
+use super::word::{Word, WordSize};
+use super::Dir;
 use crate::_generated::DMA_CHANNEL_COUNT;
 use crate::interrupt::{Interrupt, InterruptExt};
 use crate::pac::dma::vals;
@@ -246,7 +247,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             ptr as *mut u32,
             len,
             true,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -281,7 +282,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             ptr as *mut u32,
             len,
             true,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -304,7 +305,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             repeated as *const W as *mut u32,
             count,
             false,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -464,7 +465,7 @@ impl<'a, C: Channel, W: Word> DoubleBuffered<'a, C, W> {
         assert!(len > 0 && len <= 0xFFFF);
 
         let dir = Dir::PeripheralToMemory;
-        let data_size = W::bits();
+        let data_size = W::size();
 
         let channel_number = channel.num();
         let dma = channel.regs();

embassy-stm32/src/dma/gpdma.rs

@@ -9,7 +9,8 @@ use embassy_cortex_m::interrupt::Priority;
 use embassy_hal_common::{into_ref, Peripheral, PeripheralRef};
 use embassy_sync::waitqueue::AtomicWaker;
 
-use super::{Dir, Word, WordSize};
+use super::word::{Word, WordSize};
+use super::Dir;
 use crate::_generated::GPDMA_CHANNEL_COUNT;
 use crate::interrupt::{Interrupt, InterruptExt};
 use crate::pac;
@@ -165,7 +166,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             ptr as *mut u32,
             len,
             true,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -200,7 +201,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             ptr as *mut u32,
             len,
             true,
-            W::bits(),
+            W::size(),
             options,
         )
     }
@@ -223,7 +224,7 @@ impl<'a, C: Channel> Transfer<'a, C> {
             repeated as *const W as *mut u32,
             count,
             false,
-            W::bits(),
+            W::size(),
             options,
         )
     }

embassy-stm32/src/dma/mod.rs

@@ -21,6 +21,8 @@ pub use gpdma::*;
 #[cfg(dmamux)]
 mod dmamux;
 
+pub mod word;
+
 use core::mem;
 
 use embassy_cortex_m::interrupt::Priority;
@@ -36,53 +38,6 @@ enum Dir {
     PeripheralToMemory,
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq)]
-#[cfg_attr(feature = "defmt", derive(defmt::Format))]
-pub enum WordSize {
-    OneByte,
-    TwoBytes,
-    FourBytes,
-}
-
-impl WordSize {
-    pub fn bytes(&self) -> usize {
-        match self {
-            Self::OneByte => 1,
-            Self::TwoBytes => 2,
-            Self::FourBytes => 4,
-        }
-    }
-}
-
-mod word_sealed {
-    pub trait Word {}
-}
-
-pub trait Word: word_sealed::Word {
-    fn bits() -> WordSize;
-}
-
-impl word_sealed::Word for u8 {}
-impl Word for u8 {
-    fn bits() -> WordSize {
-        WordSize::OneByte
-    }
-}
-
-impl word_sealed::Word for u16 {}
-impl Word for u16 {
-    fn bits() -> WordSize {
-        WordSize::TwoBytes
-    }
-}
-
-impl word_sealed::Word for u32 {}
-impl Word for u32 {
-    fn bits() -> WordSize {
-        WordSize::FourBytes
-    }
-}
-
 pub struct NoDma;
 
 impl_peripheral!(NoDma);

embassy-stm32/src/dma/word.rs

@@ -0,0 +1,79 @@
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum WordSize {
+    OneByte,
+    TwoBytes,
+    FourBytes,
+}
+
+impl WordSize {
+    pub fn bytes(&self) -> usize {
+        match self {
+            Self::OneByte => 1,
+            Self::TwoBytes => 2,
+            Self::FourBytes => 4,
+        }
+    }
+}
+
+mod sealed {
+    pub trait Word {}
+}
+
+pub trait Word: sealed::Word + Default + Copy + 'static {
+    fn size() -> WordSize;
+    fn bits() -> usize;
+}
+
+macro_rules! impl_word {
+    (_, $T:ident, $bits:literal, $size:ident) => {
+        impl sealed::Word for $T {}
+        impl Word for $T {
+            fn bits() -> usize {
+                $bits
+            }
+            fn size() -> WordSize {
+                WordSize::$size
+            }
+        }
+    };
+    ($T:ident, $uX:ident, $bits:literal, $size:ident) => {
+        #[repr(transparent)]
+        #[derive(Copy, Clone, Default)]
+        pub struct $T(pub $uX);
+        impl_word!(_, $T, $bits, $size);
+    };
+}
+
+impl_word!(U1, u8, 1, OneByte);
+impl_word!(U2, u8, 2, OneByte);
+impl_word!(U3, u8, 3, OneByte);
+impl_word!(U4, u8, 4, OneByte);
+impl_word!(U5, u8, 5, OneByte);
+impl_word!(U6, u8, 6, OneByte);
+impl_word!(U7, u8, 7, OneByte);
+impl_word!(_, u8, 8, OneByte);
+impl_word!(U9, u16, 9, TwoBytes);
+impl_word!(U10, u16, 10, TwoBytes);
+impl_word!(U11, u16, 11, TwoBytes);
+impl_word!(U12, u16, 12, TwoBytes);
+impl_word!(U13, u16, 13, TwoBytes);
+impl_word!(U14, u16, 14, TwoBytes);
+impl_word!(U15, u16, 15, TwoBytes);
+impl_word!(_, u16, 16, TwoBytes);
+impl_word!(U17, u32, 17, FourBytes);
+impl_word!(U18, u32, 18, FourBytes);
+impl_word!(U19, u32, 19, FourBytes);
+impl_word!(U20, u32, 20, FourBytes);
+impl_word!(U21, u32, 21, FourBytes);
+impl_word!(U22, u32, 22, FourBytes);
+impl_word!(U23, u32, 23, FourBytes);
+impl_word!(U24, u32, 24, FourBytes);
+impl_word!(U25, u32, 25, FourBytes);
+impl_word!(U26, u32, 26, FourBytes);
+impl_word!(U27, u32, 27, FourBytes);
+impl_word!(U28, u32, 28, FourBytes);
+impl_word!(U29, u32, 29, FourBytes);
+impl_word!(U30, u32, 30, FourBytes);
+impl_word!(U31, u32, 31, FourBytes);
+impl_word!(_, u32, 32, FourBytes);

embassy-stm32/src/spi/mod.rs

@@ -7,8 +7,7 @@ use embassy_futures::join::join;
 use embassy_hal_common::{into_ref, PeripheralRef};
 pub use embedded_hal_02::spi::{Mode, Phase, Polarity, MODE_0, MODE_1, MODE_2, MODE_3};
 
-use self::sealed::WordSize;
+use crate::dma::{slice_ptr_parts, word, Transfer};
-use crate::dma::{slice_ptr_parts, Transfer};
 use crate::gpio::sealed::{AFType, Pin as _};
 use crate::gpio::{AnyPin, Pull};
 use crate::pac::spi::{regs, vals, Spi as Regs};
@@ -78,7 +77,7 @@ pub struct Spi<'d, T: Instance, Tx, Rx> {
     miso: Option<PeripheralRef<'d, AnyPin>>,
     txdma: PeripheralRef<'d, Tx>,
     rxdma: PeripheralRef<'d, Rx>,
-    current_word_size: WordSize,
+    current_word_size: word_impl::Config,
 }
 
 impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
@@ -178,6 +177,23 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
         )
     }
 
+    pub fn new_txonly_nosck(
+        peri: impl Peripheral<P = T> + 'd,
+        mosi: impl Peripheral<P = impl MosiPin<T>> + 'd,
+        txdma: impl Peripheral<P = Tx> + 'd,
+        rxdma: impl Peripheral<P = Rx> + 'd, // TODO: remove
+        freq: Hertz,
+        config: Config,
+    ) -> Self {
+        into_ref!(mosi);
+        unsafe {
+            mosi.set_as_af_pull(mosi.af_num(), AFType::OutputPushPull, Pull::Down);
+            mosi.set_speed(crate::gpio::Speed::Medium);
+        }
+
+        Self::new_inner(peri, None, Some(mosi.map_into()), None, txdma, rxdma, freq, config)
+    }
+
     /// Useful for on chip peripherals like SUBGHZ which are hardwired.
     /// The bus can optionally be exposed externally with `Spi::new()` still.
     #[allow(dead_code)]
@@ -234,14 +250,15 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
                 if mosi.is_none() {
                     w.set_rxonly(vals::Rxonly::OUTPUTDISABLED);
                 }
-                w.set_dff(WordSize::EightBit.dff())
+                w.set_dff(<u8 as sealed::Word>::CONFIG)
             });
         }
         #[cfg(spi_v2)]
         unsafe {
             T::REGS.cr2().modify(|w| {
-                w.set_frxth(WordSize::EightBit.frxth());
+                let (ds, frxth) = <u8 as sealed::Word>::CONFIG;
-                w.set_ds(WordSize::EightBit.ds());
+                w.set_frxth(frxth);
+                w.set_ds(ds);
                 w.set_ssoe(false);
             });
             T::REGS.cr1().modify(|w| {
@@ -279,7 +296,8 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
             T::REGS.cfg1().modify(|w| {
                 w.set_crcen(false);
                 w.set_mbr(br);
-                w.set_dsize(WordSize::EightBit.dsize());
+                w.set_dsize(<u8 as sealed::Word>::CONFIG);
+                w.set_fthlv(vals::Fthlv::ONEFRAME);
             });
             T::REGS.cr2().modify(|w| {
                 w.set_tsize(0);
@@ -297,7 +315,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
             miso,
             txdma,
             rxdma,
-            current_word_size: WordSize::EightBit,
+            current_word_size: <u8 as sealed::Word>::CONFIG,
         }
     }
 
@@ -355,7 +373,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
         }
     }
 
-    fn set_word_size(&mut self, word_size: WordSize) {
+    fn set_word_size(&mut self, word_size: word_impl::Config) {
         if self.current_word_size == word_size {
             return;
         }
@@ -364,7 +382,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
         unsafe {
             T::REGS.cr1().modify(|reg| {
                 reg.set_spe(false);
-                reg.set_dff(word_size.dff())
+                reg.set_dff(word_size)
             });
             T::REGS.cr1().modify(|reg| {
                 reg.set_spe(true);
@@ -376,8 +394,8 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
                 w.set_spe(false);
             });
             T::REGS.cr2().modify(|w| {
-                w.set_frxth(word_size.frxth());
+                w.set_frxth(word_size.1);
-                w.set_ds(word_size.ds());
+                w.set_ds(word_size.0);
             });
             T::REGS.cr1().modify(|w| {
                 w.set_spe(true);
@@ -393,7 +411,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
                 w.set_spe(false);
             });
             T::REGS.cfg1().modify(|w| {
-                w.set_dsize(word_size.dsize());
+                w.set_dsize(word_size);
             });
             T::REGS.cr1().modify(|w| {
                 w.set_csusp(false);
@@ -412,7 +430,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
             return Ok(());
         }
 
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         unsafe {
             T::REGS.cr1().modify(|w| {
                 w.set_spe(false);
@@ -450,7 +468,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
             return Ok(());
         }
 
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         unsafe {
             T::REGS.cr1().modify(|w| {
                 w.set_spe(false);
@@ -513,7 +531,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
             return Ok(());
         }
 
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         unsafe {
             T::REGS.cr1().modify(|w| {
                 w.set_spe(false);
@@ -571,7 +589,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
     pub fn blocking_write<W: Word>(&mut self, words: &[W]) -> Result<(), Error> {
         unsafe { T::REGS.cr1().modify(|w| w.set_spe(true)) }
         flush_rx_fifo(T::REGS);
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         for word in words.iter() {
             let _ = transfer_word(T::REGS, *word)?;
         }
@@ -581,7 +599,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
     pub fn blocking_read<W: Word>(&mut self, words: &mut [W]) -> Result<(), Error> {
         unsafe { T::REGS.cr1().modify(|w| w.set_spe(true)) }
         flush_rx_fifo(T::REGS);
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         for word in words.iter_mut() {
             *word = transfer_word(T::REGS, W::default())?;
         }
@@ -591,7 +609,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
     pub fn blocking_transfer_in_place<W: Word>(&mut self, words: &mut [W]) -> Result<(), Error> {
         unsafe { T::REGS.cr1().modify(|w| w.set_spe(true)) }
         flush_rx_fifo(T::REGS);
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         for word in words.iter_mut() {
             *word = transfer_word(T::REGS, *word)?;
         }
@@ -601,7 +619,7 @@ impl<'d, T: Instance, Tx, Rx> Spi<'d, T, Tx, Rx> {
     pub fn blocking_transfer<W: Word>(&mut self, read: &mut [W], write: &[W]) -> Result<(), Error> {
         unsafe { T::REGS.cr1().modify(|w| w.set_spe(true)) }
         flush_rx_fifo(T::REGS);
-        self.set_word_size(W::WORDSIZE);
+        self.set_word_size(W::CONFIG);
         let len = read.len().max(write.len());
         for i in 0..len {
             let wb = write.get(i).copied().unwrap_or_default();
@@ -933,70 +951,89 @@ pub(crate) mod sealed {
         const REGS: Regs;
     }
 
-    pub trait Word: Copy + 'static {
+    pub trait Word {
-        const WORDSIZE: WordSize;
+        const CONFIG: word_impl::Config;
-    }
-
-    impl Word for u8 {
-        const WORDSIZE: WordSize = WordSize::EightBit;
-    }
-    impl Word for u16 {
-        const WORDSIZE: WordSize = WordSize::SixteenBit;
-    }
-
-    #[derive(Copy, Clone, PartialOrd, PartialEq)]
-    pub enum WordSize {
-        EightBit,
-        SixteenBit,
-    }
-
-    impl WordSize {
-        #[cfg(any(spi_v1, spi_f1))]
-        pub fn dff(&self) -> vals::Dff {
-            match self {
-                WordSize::EightBit => vals::Dff::EIGHTBIT,
-                WordSize::SixteenBit => vals::Dff::SIXTEENBIT,
-            }
-        }
-
-        #[cfg(spi_v2)]
-        pub fn ds(&self) -> vals::Ds {
-            match self {
-                WordSize::EightBit => vals::Ds::EIGHTBIT,
-                WordSize::SixteenBit => vals::Ds::SIXTEENBIT,
-            }
-        }
-
-        #[cfg(spi_v2)]
-        pub fn frxth(&self) -> vals::Frxth {
-            match self {
-                WordSize::EightBit => vals::Frxth::QUARTER,
-                WordSize::SixteenBit => vals::Frxth::HALF,
-            }
-        }
-
-        #[cfg(any(spi_v3, spi_v4, spi_v5))]
-        pub fn dsize(&self) -> u8 {
-            match self {
-                WordSize::EightBit => 0b0111,
-                WordSize::SixteenBit => 0b1111,
-            }
-        }
-
-        #[cfg(any(spi_v3, spi_v4, spi_v5))]
-        pub fn _frxth(&self) -> vals::Fthlv {
-            match self {
-                WordSize::EightBit => vals::Fthlv::ONEFRAME,
-                WordSize::SixteenBit => vals::Fthlv::ONEFRAME,
-            }
-        }
     }
 }
 
-pub trait Word: Copy + 'static + sealed::Word + Default + crate::dma::Word {}
+pub trait Word: word::Word + sealed::Word {}
 
-impl Word for u8 {}
+macro_rules! impl_word {
-impl Word for u16 {}
+    ($T:ty, $config:expr) => {
+        impl sealed::Word for $T {
+            const CONFIG: Config = $config;
+        }
+        impl Word for $T {}
+    };
+}
+
+#[cfg(any(spi_v1, spi_f1))]
+mod word_impl {
+    use super::*;
+
+    pub type Config = vals::Dff;
+
+    impl_word!(u8, vals::Dff::EIGHTBIT);
+    impl_word!(u16, vals::Dff::SIXTEENBIT);
+}
+
+#[cfg(any(spi_v2))]
+mod word_impl {
+    use super::*;
+
+    pub type Config = (vals::Ds, vals::Frxth);
+
+    impl_word!(word::U4, (vals::Ds::FOURBIT, vals::Frxth::QUARTER));
+    impl_word!(word::U5, (vals::Ds::FIVEBIT, vals::Frxth::QUARTER));
+    impl_word!(word::U6, (vals::Ds::SIXBIT, vals::Frxth::QUARTER));
+    impl_word!(word::U7, (vals::Ds::SEVENBIT, vals::Frxth::QUARTER));
+    impl_word!(u8, (vals::Ds::EIGHTBIT, vals::Frxth::QUARTER));
+    impl_word!(word::U9, (vals::Ds::NINEBIT, vals::Frxth::HALF));
+    impl_word!(word::U10, (vals::Ds::TENBIT, vals::Frxth::HALF));
+    impl_word!(word::U11, (vals::Ds::ELEVENBIT, vals::Frxth::HALF));
+    impl_word!(word::U12, (vals::Ds::TWELVEBIT, vals::Frxth::HALF));
+    impl_word!(word::U13, (vals::Ds::THIRTEENBIT, vals::Frxth::HALF));
+    impl_word!(word::U14, (vals::Ds::FOURTEENBIT, vals::Frxth::HALF));
+    impl_word!(word::U15, (vals::Ds::FIFTEENBIT, vals::Frxth::HALF));
+    impl_word!(u16, (vals::Ds::SIXTEENBIT, vals::Frxth::HALF));
+}
+
+#[cfg(any(spi_v3, spi_v4, spi_v5))]
+mod word_impl {
+    use super::*;
+
+    pub type Config = u8;
+
+    impl_word!(word::U4, 4 - 1);
+    impl_word!(word::U5, 5 - 1);
+    impl_word!(word::U6, 6 - 1);
+    impl_word!(word::U7, 7 - 1);
+    impl_word!(u8, 8 - 1);
+    impl_word!(word::U9, 9 - 1);
+    impl_word!(word::U10, 10 - 1);
+    impl_word!(word::U11, 11 - 1);
+    impl_word!(word::U12, 12 - 1);
+    impl_word!(word::U13, 13 - 1);
+    impl_word!(word::U14, 14 - 1);
+    impl_word!(word::U15, 15 - 1);
+    impl_word!(u16, 16 - 1);
+    impl_word!(word::U17, 17 - 1);
+    impl_word!(word::U18, 18 - 1);
+    impl_word!(word::U19, 19 - 1);
+    impl_word!(word::U20, 20 - 1);
+    impl_word!(word::U21, 21 - 1);
+    impl_word!(word::U22, 22 - 1);
+    impl_word!(word::U23, 23 - 1);
+    impl_word!(word::U24, 24 - 1);
+    impl_word!(word::U25, 25 - 1);
+    impl_word!(word::U26, 26 - 1);
+    impl_word!(word::U27, 27 - 1);
+    impl_word!(word::U28, 28 - 1);
+    impl_word!(word::U29, 29 - 1);
+    impl_word!(word::U30, 30 - 1);
+    impl_word!(word::U31, 31 - 1);
+    impl_word!(u32, 32 - 1);
+}
 
 pub trait Instance: Peripheral<P = Self> + sealed::Instance + RccPeripheral {}
 pin_trait!(SckPin, Instance);

examples/stm32g0/src/bin/spi_neopixel.rs

@@ -0,0 +1,101 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_stm32::dma::word::U5;
+use embassy_stm32::dma::NoDma;
+use embassy_stm32::spi::{Config, Spi};
+use embassy_stm32::time::Hertz;
+use embassy_time::{Duration, Timer};
+use {defmt_rtt as _, panic_probe as _};
+
+const NR_PIXELS: usize = 15;
+const BITS_PER_PIXEL: usize = 24; // 24 for rgb, 32 for rgbw
+const TOTAL_BITS: usize = NR_PIXELS * BITS_PER_PIXEL;
+
+struct RGB {
+    r: u8,
+    g: u8,
+    b: u8,
+}
+impl Default for RGB {
+    fn default() -> RGB {
+        RGB { r: 0, g: 0, b: 0 }
+    }
+}
+pub struct Ws2812 {
+    // Note that the U5 type controls the selection of 5 bits to output
+    bitbuffer: [U5; TOTAL_BITS],
+}
+
+impl Ws2812 {
+    pub fn new() -> Ws2812 {
+        Ws2812 {
+            bitbuffer: [U5(0); TOTAL_BITS],
+        }
+    }
+    fn len(&self) -> usize {
+        return NR_PIXELS;
+    }
+    fn set(&mut self, idx: usize, rgb: RGB) {
+        self.render_color(idx, 0, rgb.g);
+        self.render_color(idx, 8, rgb.r);
+        self.render_color(idx, 16, rgb.b);
+    }
+    // transform one color byte into an array of 8 byte. Each byte in the array does represent 1 neopixel bit pattern
+    fn render_color(&mut self, pixel_idx: usize, offset: usize, color: u8) {
+        let mut bits = color as usize;
+        let mut idx = pixel_idx * BITS_PER_PIXEL + offset;
+
+        // render one bit in one spi byte. High time first, then the low time
+        // clock should be 4 Mhz, 5 bits, each bit is 0.25 us.
+        // a one bit is send as a pulse of 0.75 high -- 0.50 low
+        // a zero bit is send as a pulse of 0.50 high -- 0.75 low
+        // clock frequency for the neopixel is exact 800 khz
+        // note that the mosi output should have a resistor to ground of 10k,
+        // to assure that between the bursts the line is low
+        for _i in 0..8 {
+            if idx >= TOTAL_BITS {
+                return;
+            }
+            let pattern = match bits & 0x80 {
+                0x80 => 0b0000_1110,
+                _ => 0b000_1100,
+            };
+            bits = bits << 1;
+            self.bitbuffer[idx] = U5(pattern);
+            idx += 1;
+        }
+    }
+}
+
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
+    let p = embassy_stm32::init(Default::default());
+    info!("Start test using spi as neopixel driver");
+
+    let mut spi = Spi::new_txonly_nosck(p.SPI1, p.PB5, p.DMA1_CH3, NoDma, Hertz(4_000_000), Config::default());
+
+    let mut neopixels = Ws2812::new();
+
+    loop {
+        let mut cnt: usize = 0;
+        for _i in 0..10 {
+            for idx in 0..neopixels.len() {
+                let color = match (cnt + idx) % 3 {
+                    0 => RGB { r: 0x21, g: 0, b: 0 },
+                    1 => RGB { r: 0, g: 0x31, b: 0 },
+                    _ => RGB { r: 0, g: 0, b: 0x41 },
+                };
+                neopixels.set(idx, color);
+            }
+            cnt += 1;
+            // start sending the neopixel bit patters over spi to the neopixel string
+            spi.write(&neopixels.bitbuffer).await.ok();
+            Timer::after(Duration::from_millis(500)).await;
+        }
+        Timer::after(Duration::from_millis(1000)).await;
+    }
+}