Added support for SPI Alternate<OpenDrain> configuration on Mosi and Sck pins (#291)

* Added support for OpenDrain configuration on Sck and Mosi SPI pins.

Author: johnnyegel

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- Support for OpenDrain pin configuration on SPI CLK and MOSI pins
 - LSB/MSB bit format selection for `SPI`
 
 ### Fixed

src/spi.rs

@@ -3,6 +3,8 @@
   To construct the SPI instances, use the `Spi::spiX` functions.
 
   The pin parameter is a tuple containing `(sck, miso, mosi)` which should be configured as `(Alternate<PushPull>, Input<Floating>, Alternate<PushPull>)`.
+  As some STM32F1xx chips have 5V tolerant SPI pins, it is also possible to configure Sck and Mosi outputs as `Alternate<PushPull>`. Then
+  a simple Pull-Up to 5V can be used to use SPI on a 5V bus without a level shifter.
 
   You can also use `NoSck`, `NoMiso` or `NoMosi` if you don't want to use the pins
 
@@ -48,7 +50,7 @@ use crate::gpio::gpioa::{PA5, PA6, PA7};
 use crate::gpio::gpiob::{PB13, PB14, PB15, PB3, PB4, PB5};
 #[cfg(feature = "connectivity")]
 use crate::gpio::gpioc::{PC10, PC11, PC12};
-use crate::gpio::{Alternate, Floating, Input, PushPull};
+use crate::gpio::{Alternate, Floating, Input, OpenDrain, PushPull};
 use crate::rcc::{Clocks, Enable, GetBusFreq, Reset, APB1, APB2};
 use crate::time::Hertz;
 
@@ -144,8 +146,10 @@ macro_rules! remap {
             const REMAP: bool = $state;
         }
         impl Sck<$name> for $SCK<Alternate<PushPull>> {}
+        impl Sck<$name> for $SCK<Alternate<OpenDrain>> {}
         impl Miso<$name> for $MISO<Input<Floating>> {}
         impl Mosi<$name> for $MOSI<Alternate<PushPull>> {}
+        impl Mosi<$name> for $MOSI<Alternate<OpenDrain>> {}
     };
 }