3 files changed, 100 insertions, 7 deletions

diff --git a/embassy-usb/src/lib.rs b/embassy-usb/src/lib.rs
index f2577d4fc..eba46b892 100644
--- a/embassy-usb/src/lib.rs
+++ b/embassy-usb/src/lib.rs
@@ -11,6 +11,7 @@ pub mod descriptor;
 mod descriptor_reader;
 pub mod driver;
 pub mod types;
+pub mod util;
 
 use embassy::util::{select, Either};
 use heapless::Vec;
diff --git a/embassy-usb/src/util.rs b/embassy-usb/src/util.rs
new file mode 100644
index 000000000..ac56691b8
--- /dev/null
+++ b/embassy-usb/src/util.rs
@@ -0,0 +1,68 @@
+use embassy::channel::signal::Signal;
+use embassy::util::{select, Either};
+
+use crate::driver::Driver;
+use crate::UsbDevice;
+
+/// Am enabled usb device is a device that further receives external notifications
+/// regarding whether it is enabled or not. A common example of where this is
+/// required is when receiving notifications from the POWER peripheral that
+/// USB has been connected to or removed. The device here wraps an existing
+/// USB device, keeping it publically available so that device-oriented operations
+/// may still be performed. A signal is also provided that enables/disables the
+/// USB device, taking care of suspension and resumption. In the case of the POWER
+/// peripheral, this signal can be used from within a POWER_CLOCK interrupt
+/// handler. Alternatively, for softdevice usage where the POWER peripheral is not
+/// available, similar USB power events can be leveraged.
+pub struct EnabledUsbDevice<'d, D: Driver<'d>> {
+    pub underlying: UsbDevice<'d, D>,
+    enable_usb_signal: &'d Signal<bool>,
+}
+
+impl<'d, D: Driver<'d>> EnabledUsbDevice<'d, D> {
+    /// Wrap an existing UsbDevice and take a signal that will be used
+    /// to enable/disable it, perhaps from an external POWER_CLOCK
+    /// interrupt, or the equivalent when dealing with softdevices.
+    pub fn new(underlying: UsbDevice<'d, D>, enable_usb_signal: &'d Signal<bool>) -> Self {
+        Self {
+            underlying,
+            enable_usb_signal,
+        }
+    }
+
+    /// Runs the underlying `UsbDevice` taking care of reacting to USB becoming
+    /// enabled/disabled.
+    ///
+    /// This future may leave the bus in an invalid state if it is dropped.
+    /// After dropping the future, [`UsbDevice::disable()`] should be called
+    /// before calling any other `UsbDevice` methods to fully reset the
+    /// peripheral.
+    pub async fn run(&mut self) -> ! {
+        while !self.enable_usb_signal.wait().await {}
+        loop {
+            match select(
+                self.underlying.run_until_suspend(),
+                self.enable_usb_signal.wait(),
+            )
+            .await
+            {
+                Either::First(_) => {}
+                Either::Second(enable) => {
+                    if !enable {
+                        self.underlying.disable().await;
+                        while !self.enable_usb_signal.wait().await {}
+                    }
+                }
+            }
+            match select(self.underlying.wait_resume(), self.enable_usb_signal.wait()).await {
+                Either::First(_) => {}
+                Either::Second(enable) => {
+                    if !enable {
+                        self.underlying.disable().await;
+                        while !self.enable_usb_signal.wait().await {}
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/examples/nrf/src/bin/usb_serial.rs b/examples/nrf/src/bin/usb_serial.rs
index f108db46d..377ae8c3a 100644
--- a/examples/nrf/src/bin/usb_serial.rs
+++ b/examples/nrf/src/bin/usb_serial.rs
@@ -6,28 +6,52 @@
 use core::mem;
 
 use defmt::{info, panic};
+use embassy::channel::signal::Signal;
 use embassy::executor::Spawner;
+use embassy::interrupt::InterruptExt;
 use embassy_nrf::usb::{Driver, Instance};
-use embassy_nrf::{interrupt, pac, Peripherals};
+use embassy_nrf::{interrupt, interrupt, pac, pac, Peripherals};
 use embassy_usb::driver::EndpointError;
+use embassy_usb::util::EnabledUsbDevice;
 use embassy_usb::{Builder, Config};
 use embassy_usb_serial::{CdcAcmClass, State};
 use futures::future::join;
-use {defmt_rtt as _, panic_probe as _};
+use {defmt_rtt as _, panic_probe as _}; // global logger
+
+static ENABLE_USB: Signal<bool> = Signal::new();
+
+fn on_power_interrupt(_: *mut ()) {
+    let regs = unsafe { &*pac::POWER::ptr() };
+
+    if regs.events_usbdetected.read().bits() != 0 {
+        regs.events_usbdetected.reset();
+        info!("Vbus detected, enabling USB...");
+        ENABLE_USB.signal(true);
+    }
+
+    if regs.events_usbremoved.read().bits() != 0 {
+        regs.events_usbremoved.reset();
+        info!("Vbus removed, disabling USB...");
+        ENABLE_USB.signal(false);
+    }
+}
 
 #[embassy::main]
 async fn main(_spawner: Spawner, p: Peripherals) {
     let clock: pac::CLOCK = unsafe { mem::transmute(()) };
     let power: pac::POWER = unsafe { mem::transmute(()) };
 
+    let power_irq = interrupt::take!(POWER_CLOCK);
+    power_irq.set_handler(on_power_interrupt);
+    power_irq.unpend();
+    power_irq.enable();
+
+    power.intenset.write(|w| w.usbdetected().set().usbremoved().set());
+
     info!("Enabling ext hfosc...");
     clock.tasks_hfclkstart.write(|w| unsafe { w.bits(1) });
     while clock.events_hfclkstarted.read().bits() != 1 {}
 
-    info!("Waiting for vbus...");
-    while !power.usbregstatus.read().vbusdetect().is_vbus_present() {}
-    info!("vbus OK");
-
     // Create the driver, from the HAL.
     let irq = interrupt::take!(USBD);
     let driver = Driver::new(p.USBD, irq);
@@ -70,7 +94,7 @@ async fn main(_spawner: Spawner, p: Peripherals) {
     let mut class = CdcAcmClass::new(&mut builder, &mut state, 64);
 
     // Build the builder.
-    let mut usb = builder.build();
+    let mut usb = EnabledUsbDevice::new(builder.build(), &ENABLE_USB);
 
     // Run the USB device.
     let usb_fut = usb.run();