Refactor spi modules to improve structure

Make several improvements to the `sercom::v2::spi` module:
- Introduce a `Registers` type that acts as a task-focused API for the
  registers, as opposed to the register-focused API of the PAC. This
  abstraction also serves to remove interior mutability of the PAC
  struct and lets us implement `Sync` for `Registers`
- Add a `Capability` trait and three corresponding types: `Rx`, `Tx` and
  `Duplex`. Add a `Capability` type parameter to the `Spi` struct and
  use it to differentiate the various embedded HAL trait
  implementations. This is a better solution than the previous approach,
  which was a set of marker traits implemented on `Pads` types.
- Combine the `thumbv6m` and `thumbv7em` modules to reuse more code. The
  major differences between the two chips come in the `Pads` type, and
  the `Length` and `CharSize` types. Introduce a `Size` trait that
  essentially acts a trait alias for either `Length` or `CharSize`.
  Split up the modules and use conditional imports to handle everything
  correctly for the three different chips.

Because the `spi` module is no longer split between the two
chip-specific modules, also consolidate the `impl_pad` modules as well.

Finally, improve the documentation for the `spi` module itself, as well
as for the embedded HAL trait implementations.

boards/feather_m0/src/lib.rs

@@ -214,7 +214,7 @@ pub type SpiPads = spi::Pads<Sercom4, Miso, Mosi, Sclk>;
 /// SPI master for the labelled SPI peripheral
 ///
 /// This type implements [`FullDuplex<u8>`](ehal::spi::FullDuplex).
-pub type Spi = spi::Spi<spi::Config<SpiPads>>;
+pub type Spi = spi::Spi<spi::Config<SpiPads>, spi::Duplex>;
 
 /// Convenience for setting up the labelled SPI peripheral.
 /// This powers up SERCOM4 and configures it for use as an

boards/p1am_100/src/lib.rs

@@ -203,7 +203,7 @@ const BASE_CONTROLLER_SPI_MODE: embedded_hal::spi::Mode = spi::MODE_2;
 
 pub type Spi0Pads = spi::Pads<Sercom1, Spi0Miso, Spi0Mosi, Spi0Sck>;
 
-pub type Spi0 = spi::Spi<spi::Config<Spi0Pads>>;
+pub type Spi0 = spi::Spi<spi::Config<Spi0Pads>, spi::Duplex>;
 
 /// Convenience for setting up the labeled SPI0 peripheral.
 /// SPI0 has the P1AM base controller connected.
@@ -228,7 +228,7 @@ pub fn base_controller_spi(
 
 type SdPads = spi::Pads<Sercom2, SdMiso, SdMosi, SdSck>;
 
-pub type SdSpi = spi::Spi<spi::Config<SdPads>>;
+pub type SdSpi = spi::Spi<spi::Config<SdPads>, spi::Duplex>;
 
 /// Convenience for setting up the labeled SPI2 peripheral.
 /// SPI2 has the microSD card slot connected.

boards/pygamer/src/pins.rs

@@ -582,7 +582,7 @@ pub struct Display {
 }
 
 pub type TftPads = spi::Pads<Sercom4, IoSet1, NoneT, TftMosi, TftSclk>;
-pub type TftSpi = spi::Spi<spi::Config<TftPads>>;
+pub type TftSpi = spi::Spi<spi::Config<TftPads>, spi::Tx>;
 
 #[cfg(feature = "unproven")]
 impl Display {
@@ -658,7 +658,7 @@ pub struct SPI {
 pub type SpiPads = spi::Pads<Sercom1, UndocIoSet1, SpiMiso, SpiMosi, SpiSclk>;
 
 /// SPI master for the labelled pins
-pub type Spi = spi::Spi<spi::Config<SpiPads>>;
+pub type Spi = spi::Spi<spi::Config<SpiPads>, spi::Duplex>;
 
 impl SPI {
     /// Convenience for setting up the labelled pins to operate

boards/wio_terminal/src/display.rs

@@ -4,7 +4,7 @@ use atsamd_hal::gpio::*;
 use atsamd_hal::hal::blocking::delay::DelayMs;
 use atsamd_hal::hal::spi::{Phase, Polarity};
 use atsamd_hal::prelude::*;
-use atsamd_hal::sercom::v2::spi::{self, Spi};
+use atsamd_hal::sercom::v2::spi;
 use atsamd_hal::sercom::v2::{IoSet4, Sercom7};
 use atsamd_hal::target_device::{MCLK, SERCOM7};
 use atsamd_hal::time::Hertz;
@@ -36,11 +36,12 @@ pub struct Display {
     pub backlight: Pc5<Input<Floating>>,
 }
 
-pub type SpiPads = spi::PadsFromIds<Sercom7, IoSet4, NoneT, PB19, PB20>;
+pub type LcdPads = spi::PadsFromIds<Sercom7, IoSet4, NoneT, PB19, PB20>;
+pub type LcdSpi = spi::Spi<spi::Config<LcdPads>, spi::Tx>;
 
 /// Type alias for the ILI9341 LCD display.
 pub type LCD = Ili9341<
-    SPIInterface<Spi<spi::Config<SpiPads>>, Pc6<Output<PushPull>>, Pb21<Output<PushPull>>>,
+    SPIInterface<LcdSpi, Pc6<Output<PushPull>>, Pb21<Output<PushPull>>>,
     Pc7<Output<PushPull>>,
 >;
 

hal/src/sercom/v2.rs

@@ -24,19 +24,16 @@ use pac::{SERCOM4, SERCOM5};
 #[cfg(feature = "min-samd51n")]
 use pac::{SERCOM6, SERCOM7};
 
-#[cfg(any(feature = "samd11", feature = "samd21"))]
-pub use crate::common::thumbv6m::sercom::v2::*;
-
-#[cfg(feature = "min-samd51g")]
-pub use crate::common::thumbv7em::sercom::v2::*;
-
 #[cfg(feature = "dma")]
 use crate::common::dmac::TriggerSource;
+
 use crate::typelevel::Sealed;
 
 pub mod pad;
 pub use pad::*;
 
+pub mod spi;
+
 pub mod spi_future;
 
 //==============================================================================

hal/src/sercom/v2/pad.rs

@@ -1,4 +1,4 @@
-//! Define a SERCOM pad type
+//! Type-level tools to configure SERCOM pads
 //!
 //! This module helps configure [`Pin`]s as SERCOM pads. It provides type-level
 //! tools to convert `Pin`s to the correct [`PinMode`] and to enforce type-level
@@ -48,6 +48,14 @@ use crate::gpio::v2::OptionalPinId;
 use crate::gpio::v2::{AnyPin, OptionalPin, Pin, PinId, PinMode};
 use crate::typelevel::{NoneT, Sealed};
 
+#[cfg(any(feature = "samd11", feature = "samd21"))]
+#[path = "pad/impl_pad_thumbv6m.rs"]
+mod impl_pad;
+
+#[cfg(feature = "min-samd51g")]
+#[path = "pad/impl_pad_thumbv7em.rs"]
+mod impl_pad;
+
 //==============================================================================
 // PadNum
 //==============================================================================
@@ -252,53 +260,57 @@ where
 // IoSet
 //==============================================================================
 
-/// Type-level enum representing a SERCOM IOSET
-///
-/// See the [type-level enum] documentation for more details on the pattern.
-///
-/// [type-level enum]: crate::typelevel#type-level-enum
-#[cfg(feature = "min-samd51g")]
-pub trait IoSet: Sealed {}
-
 #[cfg(feature = "min-samd51g")]
-seq!(N in 1..=6 {
-    paste! {
-        #[doc = "Type-level variant of [`IoSet`] representing SERCOM IOSET " N]
-        ///
-        /// See the [type-level enum] documentation for more details on the
-        /// pattern.
-        ///
-        /// [type-level enum]: crate::typelevel#type-level-enum
-        pub enum IoSet#N {}
-        impl Sealed for IoSet#N {}
-        impl IoSet for IoSet#N {}
+mod ioset {
+
+    use super::*;
+
+    /// Type-level enum representing a SERCOM IOSET
+    ///
+    /// See the [type-level enum] documentation for more details on the pattern.
+    ///
+    /// [type-level enum]: crate::typelevel#type-level-enum
+    pub trait IoSet: Sealed {}
+
+    seq!(N in 1..=6 {
+        paste! {
+            #[doc = "Type-level variant of [`IoSet`] representing SERCOM IOSET " N]
+            ///
+            /// See the [type-level enum] documentation for more details on the
+            /// pattern.
+            ///
+            /// [type-level enum]: crate::typelevel#type-level-enum
+            pub enum IoSet#N {}
+            impl Sealed for IoSet#N {}
+            impl IoSet for IoSet#N {}
+        }
+    });
+
+    /// Type-level variant of [`IoSet`] representing an undocumented SERCOM
+    /// IOSET
+    ///
+    /// See the [type-level enum] documentation for more details on the pattern.
+    ///
+    /// [type-level enum]: crate::typelevel#type-level-enum
+    pub enum UndocIoSet1 {}
+    impl Sealed for UndocIoSet1 {}
+    impl IoSet for UndocIoSet1 {}
+
+    /// Type class for SERCOM pads in a given [`IoSet`]
+    ///
+    /// This trait is used to label each [`Pin`] implementing [`IsPad`] with its
+    /// corresponding [`IoSet`]\(s). Downstream types can use this trait as a
+    /// [type class] to restrict [`Pin`]s to a given [`IoSet`]. See the [type
+    /// class] documentation for more details on the pattern.
+    ///
+    /// [type class]: crate::typelevel#type-classes
+    pub trait InIoSet<I>
+    where
+        Self: IsPad,
+        I: IoSet,
+    {
     }
-});
-
-/// Type-level variant of [`IoSet`] representing an undocumented SERCOM IOSET
-///
-/// See the [type-level enum] documentation for more details on the pattern.
-///
-/// [type-level enum]: crate::typelevel#type-level-enum
-#[cfg(feature = "min-samd51g")]
-pub enum UndocIoSet1 {}
-#[cfg(feature = "min-samd51g")]
-impl Sealed for UndocIoSet1 {}
-#[cfg(feature = "min-samd51g")]
-impl IoSet for UndocIoSet1 {}
+}
 
-/// Type class for SERCOM pads in a given [`IoSet`]
-///
-/// This trait is used to label each [`Pin`] implementing [`IsPad`] with its
-/// corresponding [`IoSet`]\(s). Downstream types can use this trait as a
-/// [type class] to restrict [`Pin`]s to a given [`IoSet`]. See the [type class]
-/// documentation for more details on the pattern.
-///
-/// [type class]: crate::typelevel#type-classes
 #[cfg(feature = "min-samd51g")]
-pub trait InIoSet<I>
-where
-    Self: IsPad,
-    I: IoSet,
-{
-}
+pub use ioset::*;