Implemented a InputPin for open-drain outputs

This is behind a flag for now, since it's incredibly hacky. Hopefully,
rust-embedded/embedded-hal#29 will eventually have a nicer
fix.

Author: nightkr

Cargo.toml

@@ -6,7 +6,7 @@ keywords = ["arm", "cortex-m", "stm32", "hal"]
 license = "MIT OR Apache-2.0"
 name = "stm32f0x0-hal"
 repository = "https://github.com/PicoNodes/stm32f0x0-hal"
-version = "0.1.2"
+version = "0.1.3"
 
 [dependencies]
 cortex-m = "0.4.0"
@@ -21,3 +21,4 @@ version = "0.2.2"
 [features]
 rt = ["stm32f0x0/rt"]
 unproven = ["embedded-hal/unproven"]
+unproven_opendrain_input = []

src/gpio.rs

@@ -497,6 +497,18 @@ macro_rules! gpio {
                     }
                 }
 
+                #[cfg(feature = "unproven_opendrain_input")]
+                impl InputPin for $PXi<Output<OpenDrain>> {
+                    fn is_high(&self) -> bool {
+                        !InputPin::is_low(self)
+                    }
+
+                    fn is_low(&self) -> bool {
+                        // NOTE(unsafe) atomic read with no side effects
+                        unsafe { (*$GPIOX::ptr()).idr.read().bits() & (1 << $i) == 0 }
+                    }
+                }
+
                 #[cfg(feature = "unproven")]
                 impl<MODE> InputPin for $PXi<Input<MODE>> {
                     fn is_high(&self) -> bool {