Add ADC usage (for stm32f303 devices)

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Implement `InputPin` for `Output<OpenDrain>` pins ([#114](https://github.com/stm32-rs/stm32f3xx-hal/pull/114))
 - Support for safe one-shot DMA transfers ([#86](https://github.com/stm32-rs/stm32f3xx-hal/pull/86))
 - DMA support for serial reception and transmission ([#86](https://github.com/stm32-rs/stm32f3xx-hal/pull/86))
+- ADC support for `stm32f303` devices.
 
 ### Fixed
 

Cargo.toml

@@ -49,6 +49,7 @@ default-features = false
 panic-semihosting = "0.5"
 usb-device = "0.2"
 usbd-serial = "0.1"
+cortex-m-semihosting = "0.3"
 
 [features]
 default = ["unproven"]
@@ -110,3 +111,7 @@ required-features = ["stm32f303"]
 [[example]]
 name = "serial_dma"
 required-features = ["stm32f303"]
+
+[[example]]
+name = "adc"
+required-features = ["stm32f303"]

examples/adc.rs

@@ -0,0 +1,59 @@
+#![no_std]
+#![no_main]
+
+//! Example usage for ADC on STM32F303
+
+extern crate panic_semihosting;
+
+use cortex_m_rt::entry;
+use cortex_m_semihosting::hprintln;
+
+use stm32f3xx_hal::{adc, pac, prelude::*};
+
+#[entry]
+/// Main Thread
+fn main() -> ! {
+    // Get peripherals, clocks and freeze them
+    let mut dp = pac::Peripherals::take().unwrap();
+    let mut rcc = dp.RCC.constrain();
+    let clocks = rcc.cfgr.freeze(&mut dp.FLASH.constrain().acr);
+
+    // set up adc1
+    let mut adc1 = adc::Adc::adc1(
+        dp.ADC1, // The ADC we are going to control
+        // The following is only needed to make sure the clock signal for the ADC is set up
+        // correctly.
+        &mut dp.ADC1_2,
+        &mut rcc.ahb,
+        adc::CkMode::default(),
+        clocks,
+    );
+
+    // Set up pin PA0 as analog pin.
+    // This pin is connected to the user button on the stm32f3discovery board.
+    let mut gpio_a = dp.GPIOA.split(&mut rcc.ahb);
+    let mut adc1_in1_pin = gpio_a.pa0.into_analog(&mut gpio_a.moder, &mut gpio_a.pupdr);
+
+    // Be aware that the values in the table below depend on the input of VREF.
+    // To have a stable VREF input, put a condensator and a volt limiting diode in front of it.
+    //
+    // Also know that integer division and the ADC hardware unit always round down.
+    // To make up for those errors, see this forum entry:
+    // [https://forum.allaboutcircuits.com/threads/why-adc-1024-is-correct-and-adc-1023-is-just-plain-wrong.80018/]
+    hprintln!("
+    The ADC has a 12 bit resolution, i.e. if your reference Value is 3V:
+        approx. ADC value | approx. volt value
+        ==================+===================
+                        0 |        0 mV
+                     2048 |     1500 mV
+                     4095 |     3000 mV
+
+    If you are using a STM32F3Discovery, PA0 is connected to the User Button.
+    Pressing it should connect the user Button to to HIGH and the value should change from 0 to 4095.
+    ").expect("Error using hprintln.");
+
+    loop {
+        let adc1_in1_data: u16 = adc1.read(&mut adc1_in1_pin).expect("Error reading adc1.");
+        hprintln!("PA0 reads {}", adc1_in1_data).ok();
+    }
+}