rp: add new pio spi program

This commit adds a new PIO program which implements SPI. This allows
you to drive more than 2 SPI buses by using PIO state machines as
additional duplex SPI interfaces.

The driver supports both blocking and async modes of operation and
exclusively uses the DMA for async IO.

2 files changed, 434 insertions, 0 deletions

diff --git a/embassy-rp/src/pio_programs/mod.rs b/embassy-rp/src/pio_programs/mod.rs
index 8eac328b3..d05ba3884 100644
--- a/embassy-rp/src/pio_programs/mod.rs
+++ b/embassy-rp/src/pio_programs/mod.rs
@@ -6,6 +6,7 @@ pub mod i2s;
 pub mod onewire;
 pub mod pwm;
 pub mod rotary_encoder;
+pub mod spi;
 pub mod stepper;
 pub mod uart;
 pub mod ws2812;
diff --git a/embassy-rp/src/pio_programs/spi.rs b/embassy-rp/src/pio_programs/spi.rs
new file mode 100644
index 000000000..27d401fc9
--- /dev/null
+++ b/embassy-rp/src/pio_programs/spi.rs
@@ -0,0 +1,433 @@
+//! PIO backed SPi drivers
+
+use core::marker::PhantomData;
+
+use embassy_futures::join::join;
+use embassy_hal_internal::Peri;
+use embedded_hal_02::spi::{Phase, Polarity};
+use fixed::{traits::ToFixed, types::extra::U8};
+
+use crate::{
+    clocks::clk_sys_freq,
+    dma::{AnyChannel, Channel},
+    gpio::Level,
+    pio::{Common, Direction, Instance, LoadedProgram, PioPin, ShiftDirection, StateMachine},
+    spi::{Async, Blocking, Mode},
+};
+
+/// This struct represents a uart tx program loaded into pio instruction memory.
+pub struct PioSpiProgram<'d, PIO: crate::pio::Instance> {
+    prg: LoadedProgram<'d, PIO>,
+}
+
+impl<'d, PIO: crate::pio::Instance> PioSpiProgram<'d, PIO> {
+    /// Load the spi program into the given pio
+    pub fn new(common: &mut crate::pio::Common<'d, PIO>, phase: Phase) -> Self {
+        // These PIO programs are taken straight from the datasheet (3.6.1 in
+        // RP2040 datasheet, 11.6.1 in RP2350 datasheet)
+
+        // Pin assignments:
+        // - SCK is side-set pin 0
+        // - MOSI is OUT pin 0
+        // - MISO is IN pin 0
+        //
+        // Autopush and autopull must be enabled, and the serial frame size is set by
+        // configuring the push/pull threshold. Shift left/right is fine, but you must
+        // justify the data yourself. This is done most conveniently for frame sizes of
+        // 8 or 16 bits by using the narrow store replication and narrow load byte
+        // picking behaviour of RP2040's IO fabric.
+
+        let prg = match phase {
+            Phase::CaptureOnFirstTransition => {
+                let prg = pio::pio_asm!(
+                    r#"
+                        .side_set 1
+
+                        ; Clock phase = 0: data is captured on the leading edge of each SCK pulse, and
+                        ; transitions on the trailing edge, or some time before the first leading edge.
+
+                        out pins, 1 side 0 [1] ; Stall here on empty (sideset proceeds even if
+                        in pins, 1  side 1 [1] ; instruction stalls, so we stall with SCK low)
+                    "#
+                );
+
+                common.load_program(&prg.program)
+            }
+            Phase::CaptureOnSecondTransition => {
+                let prg = pio::pio_asm!(
+                    r#"
+                        .side_set 1
+
+                        ; Clock phase = 1: data transitions on the leading edge of each SCK pulse, and
+                        ; is captured on the trailing edge.
+
+                        out x, 1    side 0     ; Stall here on empty (keep SCK deasserted)
+                        mov pins, x side 1 [1] ; Output data, assert SCK (mov pins uses OUT mapping)
+                        in pins, 1  side 0     ; Input data, deassert SCK
+                    "#
+                );
+
+                common.load_program(&prg.program)
+            }
+        };
+
+        Self { prg }
+    }
+}
+
+/// PIO SPI errors.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+#[non_exhaustive]
+pub enum Error {
+    // No errors for now
+}
+
+/// PIO based Spi driver.
+///
+/// This driver is less flexible than the hardware backed one. Configuration can
+/// not be changed at runtime.
+pub struct Spi<'d, PIO: Instance, const SM: usize, M: Mode> {
+    sm: StateMachine<'d, PIO, SM>,
+    tx_dma: Option<Peri<'d, AnyChannel>>,
+    rx_dma: Option<Peri<'d, AnyChannel>>,
+    phantom: PhantomData<M>,
+}
+
+/// PIO SPI configuration.
+#[non_exhaustive]
+#[derive(Clone)]
+pub struct Config {
+    /// Frequency (Hz).
+    pub frequency: u32,
+    /// Polarity.
+    pub polarity: Polarity,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            frequency: 1_000_000,
+            polarity: Polarity::IdleLow,
+        }
+    }
+}
+
+impl<'d, PIO: Instance, const SM: usize, M: Mode> Spi<'d, PIO, SM, M> {
+    #[allow(clippy::too_many_arguments)]
+    fn new_inner(
+        pio: &mut Common<'d, PIO>,
+        mut sm: StateMachine<'d, PIO, SM>,
+        clk_pin: Peri<'d, impl PioPin>,
+        mosi_pin: Peri<'d, impl PioPin>,
+        miso_pin: Peri<'d, impl PioPin>,
+        tx_dma: Option<Peri<'d, AnyChannel>>,
+        rx_dma: Option<Peri<'d, AnyChannel>>,
+        program: &PioSpiProgram<'d, PIO>,
+        config: Config,
+    ) -> Self {
+        let mut clk_pin = pio.make_pio_pin(clk_pin);
+        let mosi_pin = pio.make_pio_pin(mosi_pin);
+        let miso_pin = pio.make_pio_pin(miso_pin);
+
+        if let Polarity::IdleHigh = config.polarity {
+            clk_pin.set_output_inversion(true);
+        } else {
+            clk_pin.set_output_inversion(false);
+        }
+
+        sm.set_pins(Level::Low, &[&clk_pin, &mosi_pin]);
+        sm.set_pin_dirs(Direction::Out, &[&clk_pin, &mosi_pin]);
+        sm.set_pin_dirs(Direction::In, &[&miso_pin]);
+
+        let mut cfg = crate::pio::Config::default();
+
+        cfg.use_program(&program.prg, &[&clk_pin]);
+        cfg.set_out_pins(&[&mosi_pin]);
+        cfg.set_in_pins(&[&miso_pin]);
+
+        cfg.shift_in.auto_fill = true;
+        cfg.shift_in.direction = ShiftDirection::Left;
+        cfg.shift_in.threshold = 8;
+
+        cfg.shift_out.auto_fill = true;
+        cfg.shift_out.direction = ShiftDirection::Left;
+        cfg.shift_out.threshold = 8;
+
+        let sys_freq = clk_sys_freq().to_fixed::<fixed::FixedU64<U8>>();
+        let target_freq = (config.frequency * 4).to_fixed::<fixed::FixedU64<U8>>();
+        cfg.clock_divider = (sys_freq / target_freq).to_fixed();
+
+        sm.set_config(&cfg);
+        sm.set_enable(true);
+
+        Self {
+            sm,
+            tx_dma,
+            rx_dma,
+            phantom: PhantomData,
+        }
+    }
+
+    fn blocking_read_u8(&mut self) -> Result<u8, Error> {
+        while self.sm.rx().empty() {}
+        let value = self.sm.rx().pull() as u8;
+
+        Ok(value)
+    }
+
+    fn blocking_write_u8(&mut self, v: u8) -> Result<(), Error> {
+        let value = u32::from_be_bytes([v, 0, 0, 0]);
+
+        while !self.sm.tx().try_push(value) {}
+
+        // need to clear here for flush to work correctly
+        self.sm.tx().stalled();
+
+        Ok(())
+    }
+
+    /// Read data from SPI blocking execution until done.
+    pub fn blocking_read(&mut self, data: &mut [u8]) -> Result<(), Error> {
+        for v in data {
+            self.blocking_write_u8(0)?;
+            *v = self.blocking_read_u8()?;
+        }
+        self.flush()?;
+        Ok(())
+    }
+
+    /// Write data to SPI blocking execution until done.
+    pub fn blocking_write(&mut self, data: &[u8]) -> Result<(), Error> {
+        for v in data {
+            self.blocking_write_u8(*v)?;
+            let _ = self.blocking_read_u8()?;
+        }
+        self.flush()?;
+        Ok(())
+    }
+
+    /// Transfer data to SPI blocking execution until done.
+    pub fn blocking_transfer(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Error> {
+        let len = read.len().max(write.len());
+        for i in 0..len {
+            let wb = write.get(i).copied().unwrap_or(0);
+            self.blocking_write_u8(wb)?;
+
+            let rb = self.blocking_read_u8()?;
+            if let Some(r) = read.get_mut(i) {
+                *r = rb;
+            }
+        }
+        self.flush()?;
+        Ok(())
+    }
+
+    /// Transfer data in place to SPI blocking execution until done.
+    pub fn blocking_transfer_in_place(&mut self, data: &mut [u8]) -> Result<(), Error> {
+        for v in data {
+            self.blocking_write_u8(*v)?;
+            *v = self.blocking_read_u8()?;
+        }
+        self.flush()?;
+        Ok(())
+    }
+
+    /// Block execution until SPI is done.
+    pub fn flush(&mut self) -> Result<(), Error> {
+        // Wait for all words in the FIFO to have been pulled by the SM
+        while !self.sm.tx().empty() {}
+
+        // Wait for last value to be written out to the wire
+        while !self.sm.tx().stalled() {}
+
+        Ok(())
+    }
+}
+
+impl<'d, PIO: Instance, const SM: usize> Spi<'d, PIO, SM, Blocking> {
+    /// Create an SPI driver in blocking mode.
+    pub fn new_blocking(
+        pio: &mut Common<'d, PIO>,
+        sm: StateMachine<'d, PIO, SM>,
+        clk: Peri<'d, impl PioPin>,
+        mosi: Peri<'d, impl PioPin>,
+        miso: Peri<'d, impl PioPin>,
+        program: &PioSpiProgram<'d, PIO>,
+        config: Config,
+    ) -> Self {
+        Self::new_inner(pio, sm, clk, mosi, miso, None, None, program, config)
+    }
+}
+
+impl<'d, PIO: Instance, const SM: usize> Spi<'d, PIO, SM, Async> {
+    /// Create an SPI driver in async mode supporting DMA operations.
+    #[allow(clippy::too_many_arguments)]
+    pub fn new(
+        pio: &mut Common<'d, PIO>,
+        sm: StateMachine<'d, PIO, SM>,
+        clk: Peri<'d, impl PioPin>,
+        mosi: Peri<'d, impl PioPin>,
+        miso: Peri<'d, impl PioPin>,
+        tx_dma: Peri<'d, impl Channel>,
+        rx_dma: Peri<'d, impl Channel>,
+        program: &PioSpiProgram<'d, PIO>,
+        config: Config,
+    ) -> Self {
+        Self::new_inner(
+            pio,
+            sm,
+            clk,
+            mosi,
+            miso,
+            Some(tx_dma.into()),
+            Some(rx_dma.into()),
+            program,
+            config,
+        )
+    }
+
+    /// Read data from SPI using DMA.
+    pub async fn read(&mut self, buffer: &mut [u8]) -> Result<(), Error> {
+        let (rx, tx) = self.sm.rx_tx();
+
+        let len = buffer.len();
+
+        let rx_ch = self.rx_dma.as_mut().unwrap().reborrow();
+        let rx_transfer = rx.dma_pull(rx_ch, buffer, false);
+
+        let tx_ch = self.tx_dma.as_mut().unwrap().reborrow();
+        let tx_transfer = tx.dma_push_repeated::<_, u8>(tx_ch, len);
+
+        join(tx_transfer, rx_transfer).await;
+
+        Ok(())
+    }
+
+    /// Write data to SPI using DMA.
+    pub async fn write(&mut self, buffer: &[u8]) -> Result<(), Error> {
+        let (rx, tx) = self.sm.rx_tx();
+
+        let rx_ch = self.rx_dma.as_mut().unwrap().reborrow();
+        let rx_transfer = rx.dma_pull_repeated::<_, u8>(rx_ch, buffer.len());
+
+        let tx_ch = self.tx_dma.as_mut().unwrap().reborrow();
+        let tx_transfer = tx.dma_push(tx_ch, buffer, false);
+
+        join(tx_transfer, rx_transfer).await;
+
+        Ok(())
+    }
+
+    /// Transfer data to SPI using DMA.
+    pub async fn transfer(&mut self, rx_buffer: &mut [u8], tx_buffer: &[u8]) -> Result<(), Error> {
+        self.transfer_inner(rx_buffer, tx_buffer).await
+    }
+
+    /// Transfer data in place to SPI using DMA.
+    pub async fn transfer_in_place(&mut self, words: &mut [u8]) -> Result<(), Error> {
+        self.transfer_inner(words, words).await
+    }
+
+    async fn transfer_inner(&mut self, rx_buffer: *mut [u8], tx_buffer: *const [u8]) -> Result<(), Error> {
+        let (rx, tx) = self.sm.rx_tx();
+
+        let mut rx_ch = self.rx_dma.as_mut().unwrap().reborrow();
+        let rx_transfer = async {
+            rx.dma_pull(rx_ch.reborrow(), unsafe { &mut *rx_buffer }, false).await;
+
+            if tx_buffer.len() > rx_buffer.len() {
+                let read_bytes_len = tx_buffer.len() - rx_buffer.len();
+
+                rx.dma_pull_repeated::<_, u8>(rx_ch, read_bytes_len).await;
+            }
+        };
+
+        let mut tx_ch = self.tx_dma.as_mut().unwrap().reborrow();
+        let tx_transfer = async {
+            tx.dma_push(tx_ch.reborrow(), unsafe { &*tx_buffer }, false).await;
+
+            if rx_buffer.len() > tx_buffer.len() {
+                let write_bytes_len = rx_buffer.len() - tx_buffer.len();
+
+                tx.dma_push_repeated::<_, u8>(tx_ch, write_bytes_len).await;
+            }
+        };
+
+        join(tx_transfer, rx_transfer).await;
+
+        Ok(())
+    }
+}
+
+// ====================
+
+impl<'d, PIO: Instance, const SM: usize, M: Mode> embedded_hal_02::blocking::spi::Transfer<u8> for Spi<'d, PIO, SM, M> {
+    type Error = Error;
+    fn transfer<'w>(&mut self, words: &'w mut [u8]) -> Result<&'w [u8], Self::Error> {
+        self.blocking_transfer_in_place(words)?;
+        Ok(words)
+    }
+}
+
+impl<'d, PIO: Instance, const SM: usize, M: Mode> embedded_hal_02::blocking::spi::Write<u8> for Spi<'d, PIO, SM, M> {
+    type Error = Error;
+
+    fn write(&mut self, words: &[u8]) -> Result<(), Self::Error> {
+        self.blocking_write(words)
+    }
+}
+
+impl embedded_hal_1::spi::Error for Error {
+    fn kind(&self) -> embedded_hal_1::spi::ErrorKind {
+        match *self {}
+    }
+}
+
+impl<'d, PIO: Instance, const SM: usize, M: Mode> embedded_hal_1::spi::ErrorType for Spi<'d, PIO, SM, M> {
+    type Error = Error;
+}
+
+impl<'d, PIO: Instance, const SM: usize, M: Mode> embedded_hal_1::spi::SpiBus<u8> for Spi<'d, PIO, SM, M> {
+    fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    fn read(&mut self, words: &mut [u8]) -> Result<(), Self::Error> {
+        self.blocking_transfer(words, &[])
+    }
+
+    fn write(&mut self, words: &[u8]) -> Result<(), Self::Error> {
+        self.blocking_write(words)
+    }
+
+    fn transfer(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Self::Error> {
+        self.blocking_transfer(read, write)
+    }
+
+    fn transfer_in_place(&mut self, words: &mut [u8]) -> Result<(), Self::Error> {
+        self.blocking_transfer_in_place(words)
+    }
+}
+
+impl<'d, PIO: Instance, const SM: usize> embedded_hal_async::spi::SpiBus<u8> for Spi<'d, PIO, SM, Async> {
+    async fn flush(&mut self) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn write(&mut self, words: &[u8]) -> Result<(), Self::Error> {
+        self.write(words).await
+    }
+
+    async fn read(&mut self, words: &mut [u8]) -> Result<(), Self::Error> {
+        self.read(words).await
+    }
+
+    async fn transfer(&mut self, read: &mut [u8], write: &[u8]) -> Result<(), Self::Error> {
+        self.transfer(read, write).await
+    }
+
+    async fn transfer_in_place(&mut self, words: &mut [u8]) -> Result<(), Self::Error> {
+        self.transfer_in_place(words).await
+    }
+}