Add basic atmega-hal crate

Start with the new unified HAL crate for all ATmega MCUs.  Start with
support for ATmega328P's GPIO pins and USART peripheral.

Instead of, like the previous HAL, exposing `pac::Peripherals`, the HAL
now defines its own `Peripherals` struct.  This allows us to more
cleanly implement more complex peripheral support.  For example, instead
of individual fields for each port (PORTB, PORTC, PORTD, ...), the
`hal::Peripherals` only has a single field `pins`, wrapping all of the
above.

Ref: #94

Cargo.toml

@@ -25,6 +25,9 @@ members = [
     "chips/attiny85-hal",
     "chips/attiny88-hal",
 
+    # MCU HAL crates
+    "mcu/atmega-hal",
+
     # The board crates
     "boards/arduino-diecimila",
     "boards/arduino-leonardo",

mcu/atmega-hal/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "atmega-hal"
+version = "0.1.0"
+authors = ["Rahix <rahix@rahix.de>"]
+edition = "2018"
+
+[features]
+rt = ["avr-device/rt"]
+device-selected = []
+atmega328p = ["avr-device/atmega328p", "device-selected"]
+atmega328pb = ["avr-device/atmega328pb", "device-selected"]
+
+# Allow certain downstream crates to overwrite the device selection error by themselves.
+disable-device-selection-error = []
+
+[dependencies]
+avr-hal-generic = { path = "../../avr-hal-generic/" }
+
+[dependencies.avr-device]
+version = "0.3"
+
+# Because this crate has its own check that at least one device is selected, we
+# can safely "circumvent" the check in `avr-device`.
+#
+# Why would we want that?  Otherwise, as `avr-device` is compiled first, its
+# error will be shown and ours won't which leads to a degraded user experience
+# as the displayed error message does not really tell what needs to be done...
+features = ["device-selected"]

mcu/atmega-hal/src/lib.rs

@@ -0,0 +1,61 @@
+#![no_std]
+
+#[cfg(all(
+    not(feature = "device-selected"),
+    not(feature = "disable-device-selection-error")
+))]
+compile_error!(
+    "This crate requires you to specify your target chip as a feature.
+
+    Please select one of the following
+
+    * atmega328p
+    "
+);
+
+/// Reexport of `atmega328p` from `avr-device`
+#[cfg(feature = "atmega328p")]
+pub use avr_device::atmega328p as pac;
+
+/// See [`avr_device::entry`](https://docs.rs/avr-device/latest/avr_device/attr.entry.html).
+#[cfg(feature = "rt")]
+pub use avr_device::entry;
+
+pub use avr_hal_generic::clock;
+pub use avr_hal_generic::delay;
+
+#[cfg(feature = "device-selected")]
+pub mod port;
+#[cfg(feature = "device-selected")]
+pub use port::Pins;
+
+#[cfg(feature = "device-selected")]
+pub mod usart;
+#[cfg(feature = "device-selected")]
+pub use usart::Usart;
+
+pub struct RawPeripheral<P>(pub(crate) P);
+
+#[allow(non_snake_case)]
+#[cfg(feature = "device-selected")]
+pub struct Peripherals {
+    pub pins: Pins,
+    #[cfg(feature = "atmega328p")]
+    pub USART0: RawPeripheral<pac::USART0>,
+}
+
+#[cfg(feature = "device-selected")]
+impl Peripherals {
+    fn new(dp: pac::Peripherals) -> Self {
+        Self {
+            #[cfg(feature = "atmega328p")]
+            pins: Pins::new(dp.PORTB, dp.PORTC, dp.PORTD),
+            #[cfg(feature = "atmega328p")]
+            USART0: RawPeripheral(dp.USART0),
+        }
+    }
+
+    pub fn take() -> Option<Self> {
+        pac::Peripherals::take().map(Self::new)
+    }
+}

mcu/atmega-hal/src/port.rs

@@ -0,0 +1,34 @@
+#[cfg(feature = "atmega328p")]
+avr_hal_generic::impl_port_traditional! {
+    enum Ports {
+        PORTB: (crate::pac::PORTB, portb, pinb, ddrb),
+        PORTC: (crate::pac::PORTC, portc, pinc, ddrc),
+        PORTD: (crate::pac::PORTD, portd, pind, ddrd),
+    }
+
+    pub struct Pins {
+        pb0: PB0 = (crate::pac::PORTB, PORTB, 0, portb, pinb, ddrb),
+        pb1: PB1 = (crate::pac::PORTB, PORTB, 1, portb, pinb, ddrb),
+        pb2: PB2 = (crate::pac::PORTB, PORTB, 2, portb, pinb, ddrb),
+        pb3: PB3 = (crate::pac::PORTB, PORTB, 3, portb, pinb, ddrb),
+        pb4: PB4 = (crate::pac::PORTB, PORTB, 4, portb, pinb, ddrb),
+        pb5: PB5 = (crate::pac::PORTB, PORTB, 5, portb, pinb, ddrb),
+        pb6: PB6 = (crate::pac::PORTB, PORTB, 6, portb, pinb, ddrb),
+        pb7: PB7 = (crate::pac::PORTB, PORTB, 7, portb, pinb, ddrb),
+        pc0: PC0 = (crate::pac::PORTC, PORTC, 0, portc, pinc, ddrc),
+        pc1: PC1 = (crate::pac::PORTC, PORTC, 1, portc, pinc, ddrc),
+        pc2: PC2 = (crate::pac::PORTC, PORTC, 2, portc, pinc, ddrc),
+        pc3: PC3 = (crate::pac::PORTC, PORTC, 3, portc, pinc, ddrc),
+        pc4: PC4 = (crate::pac::PORTC, PORTC, 4, portc, pinc, ddrc),
+        pc5: PC5 = (crate::pac::PORTC, PORTC, 5, portc, pinc, ddrc),
+        pc6: PC6 = (crate::pac::PORTC, PORTC, 6, portc, pinc, ddrc),
+        pd0: PD0 = (crate::pac::PORTD, PORTD, 0, portd, pind, ddrd),
+        pd1: PD1 = (crate::pac::PORTD, PORTD, 1, portd, pind, ddrd),
+        pd2: PD2 = (crate::pac::PORTD, PORTD, 2, portd, pind, ddrd),
+        pd3: PD3 = (crate::pac::PORTD, PORTD, 3, portd, pind, ddrd),
+        pd4: PD4 = (crate::pac::PORTD, PORTD, 4, portd, pind, ddrd),
+        pd5: PD5 = (crate::pac::PORTD, PORTD, 5, portd, pind, ddrd),
+        pd6: PD6 = (crate::pac::PORTD, PORTD, 6, portd, pind, ddrd),
+        pd7: PD7 = (crate::pac::PORTD, PORTD, 7, portd, pind, ddrd),
+    }
+}

mcu/atmega-hal/src/usart.rs

@@ -0,0 +1,18 @@
+pub use avr_hal_generic::usart::*;
+#[allow(unused_imports)]
+use crate::port;
+
+#[cfg(feature = "atmega328p")]
+pub type Usart0<CLOCK, IMODE> = Usart<
+    crate::RawPeripheral<crate::pac::USART0>,
+    port::Pin<port::mode::Input<IMODE>, port::PD0>,
+    port::Pin<port::mode::Output, port::PD1>,
+    CLOCK,
+>;
+#[cfg(feature = "atmega328p")]
+avr_hal_generic::impl_usart_traditional! {
+    peripheral: crate::RawPeripheral<crate::pac::USART0>,
+    register_suffix: 0,
+    rx: port::PD0,
+    tx: port::PD1,
+}