Add USB driver

Cargo.toml

@@ -37,6 +37,7 @@ embedded-hal = { version = "0.2", features = ["unproven"] }
 stm32f0 = "0.8"
 nb = "0.1"
 void = { version = "1.0", default-features = false }
+stm32-usbd = { version = "0.5.0", features = ["ram_access_2x16"], optional = true }
 
 [dev-dependencies]
 panic-halt = "0.2"

src/lib.rs

@@ -69,5 +69,15 @@ pub mod timers;
     feature = "stm32f098",
 ))]
 pub mod tsc;
+#[cfg(all(
+    feature = "stm32-usbd",
+    any(
+        feature = "stm32f042",
+        feature = "stm32f048",
+        feature = "stm32f072",
+        feature = "stm32f078",
+    )
+))]
+pub mod usb;
 #[cfg(feature = "device-selected")]
 pub mod watchdog;

src/usb.rs

@@ -0,0 +1,44 @@
+//! USB peripheral
+
+use crate::stm32::{RCC, USB};
+use stm32_usbd::UsbPeripheral;
+
+use crate::gpio::gpioa::{PA11, PA12};
+use crate::gpio::{Floating, Input};
+pub use stm32_usbd::UsbBus;
+
+pub struct Peripheral {
+    pub usb: USB,
+    pub pin_dm: PA11<Input<Floating>>,
+    pub pin_dp: PA12<Input<Floating>>,
+}
+
+unsafe impl Sync for Peripheral {}
+
+unsafe impl UsbPeripheral for Peripheral {
+    const REGISTERS: *const () = USB::ptr() as *const ();
+    const DP_PULL_UP_FEATURE: bool = true;
+    const EP_MEMORY: *const () = 0x4000_6000 as _;
+    const EP_MEMORY_SIZE: usize = 1024;
+
+    fn enable() {
+        let rcc = unsafe { (&*RCC::ptr()) };
+
+        cortex_m::interrupt::free(|_| {
+            // Enable USB peripheral
+            rcc.apb1enr.modify(|_, w| w.usben().set_bit());
+
+            // Reset USB peripheral
+            rcc.apb1rstr.modify(|_, w| w.usbrst().set_bit());
+            rcc.apb1rstr.modify(|_, w| w.usbrst().clear_bit());
+        });
+    }
+
+    fn startup_delay() {
+        // There is a chip specific startup delay. For STM32F103xx it's 1µs and this should wait for
+        // at least that long.
+        cortex_m::asm::delay(72);
+    }
+}
+
+pub type UsbBusType = UsbBus<Peripheral>;