Make Channel trait apply to a specific ADC via type parameter

Author: Brandon Matthews

src/adc.rs

@@ -3,11 +3,6 @@
 #[cfg(feature = "unproven")]
 use nb;
 
-// TODO Channel should be made generic over ADCs, but cannot due to [this reported
-// issue](https://github.com/rust-lang/rust/issues/54973). Something about blanket impls combined
-// with `type ID; const CHANNEL: Self::ID;` causes problems. So, for now, Channel can only be
-// impl'd once for a given pin.
-
 /// A marker trait to identify MCU pins that can be used as inputs to an ADC channel.
 ///
 /// This marker trait denotes an object, i.e. a GPIO pin, that is ready for use as an input to the
@@ -41,16 +36,22 @@ use nb;
 /// }
 /// ```
 #[cfg(feature = "unproven")]
-pub trait Channel {
+pub trait Channel<ADC> {
     /// Channel ID type
     ///
     /// A type used to identify this ADC channel. For example, if the ADC has eight channels, this
     /// might be a `u8`. If the ADC has multiple banks of channels, it could be a tuple, like
     /// `(u8: bank_id, u8: channel_id)`.
     type ID;
 
-    /// The specific ID that identifies this channel, for example `0` for the first ADC channel.
-    const CHANNEL: Self::ID;
+    /// Get the specific ID that identifies this channel, for example `0_u8` for the first ADC
+    /// channel, if Self::ID is u8.
+    fn channel() -> Self::ID;
+
+    // `channel` is a function due to [this reported
+    // issue](https://github.com/rust-lang/rust/issues/54973). Something about blanket impls
+    // combined with `type ID; const CHANNEL: Self::ID;` causes problems.
+    //const CHANNEL: Self::ID;
 }
 
 /// ADCs that sample on single channels per request, and do so at the time of the request.
@@ -85,7 +86,7 @@ pub trait Channel {
 /// }
 /// ```
 #[cfg(feature = "unproven")]
-pub trait OneShot<ADC, Word, Pin: Channel> {
+pub trait OneShot<ADC, Word, Pin: Channel<ADC>> {
     /// Error type returned by ADC methods
     type Error;