9 files changed, 218 insertions, 9 deletions

diff --git a/Cargo.example.toml b/Cargo.example.toml
index f072c2f96..0e9d1e32d 100644
--- a/Cargo.example.toml
+++ b/Cargo.example.toml
@@ -45,7 +45,6 @@ members = [
     #"examples/rp",
 
     # std
-    #"embassy-std",
     #"examples/std",
 ]
 
diff --git a/embassy/Cargo.toml b/embassy/Cargo.toml
index ec76299e1..0ff71ce1d 100644
--- a/embassy/Cargo.toml
+++ b/embassy/Cargo.toml
@@ -7,7 +7,7 @@ resolver = "2"
 
 [features]
 default = []
-std = ["futures/std", "embassy-traits/std"]
+std = ["futures/std", "embassy-traits/std", "time", "time-tick-1mhz"]
 
 # Enable `embassy::time` module. 
 # NOTE: This feature is only intended to be enabled by crates providing the time driver implementation.
diff --git a/embassy/src/executor/mod.rs b/embassy/src/executor/mod.rs
index e0ac566f1..5ffbe689e 100644
--- a/embassy/src/executor/mod.rs
+++ b/embassy/src/executor/mod.rs
@@ -1,4 +1,5 @@
-#[path = "arch/arm.rs"]
+#[cfg_attr(feature = "std", path = "arch/std.rs")]
+#[cfg_attr(not(feature = "std"), path = "arch/arm.rs")]
 mod arch;
 pub mod raw;
 mod spawner;
diff --git a/embassy/src/time/driver_std.rs b/embassy/src/time/driver_std.rs
new file mode 100644
index 000000000..29911c4d2
--- /dev/null
+++ b/embassy/src/time/driver_std.rs
@@ -0,0 +1,208 @@
+use atomic_polyfill::{AtomicU8, Ordering};
+use std::cell::UnsafeCell;
+use std::mem;
+use std::mem::MaybeUninit;
+use std::sync::{Condvar, Mutex, Once};
+use std::time::Duration as StdDuration;
+use std::time::Instant as StdInstant;
+use std::{ptr, thread};
+
+use crate::time::driver::{AlarmHandle, Driver};
+
+const ALARM_COUNT: usize = 4;
+
+struct AlarmState {
+    timestamp: u64,
+
+    // This is really a Option<(fn(*mut ()), *mut ())>
+    // but fn pointers aren't allowed in const yet
+    callback: *const (),
+    ctx: *mut (),
+}
+
+unsafe impl Send for AlarmState {}
+
+impl AlarmState {
+    const fn new() -> Self {
+        Self {
+            timestamp: u64::MAX,
+            callback: ptr::null(),
+            ctx: ptr::null_mut(),
+        }
+    }
+}
+
+struct TimeDriver {
+    alarm_count: AtomicU8,
+
+    once: Once,
+    alarms: UninitCell<Mutex<[AlarmState; ALARM_COUNT]>>,
+    zero_instant: UninitCell<StdInstant>,
+    signaler: UninitCell<Signaler>,
+}
+
+const ALARM_NEW: AlarmState = AlarmState::new();
+crate::time_driver_impl!(static DRIVER: TimeDriver = TimeDriver {
+    alarm_count: AtomicU8::new(0),
+
+    once: Once::new(),
+    alarms: UninitCell::uninit(),
+    zero_instant: UninitCell::uninit(),
+    signaler: UninitCell::uninit(),
+});
+
+impl TimeDriver {
+    fn init(&self) {
+        self.once.call_once(|| unsafe {
+            self.alarms.write(Mutex::new([ALARM_NEW; ALARM_COUNT]));
+            self.zero_instant.write(StdInstant::now());
+            self.signaler.write(Signaler::new());
+
+            thread::spawn(Self::alarm_thread);
+        });
+    }
+
+    fn alarm_thread() {
+        loop {
+            let now = DRIVER.now();
+
+            let mut next_alarm = u64::MAX;
+            {
+                let alarms = &mut *unsafe { DRIVER.alarms.as_ref() }.lock().unwrap();
+                for alarm in alarms {
+                    if alarm.timestamp <= now {
+                        alarm.timestamp = u64::MAX;
+
+                        // Call after clearing alarm, so the callback can set another alarm.
+
+                        // safety:
+                        // - we can ignore the possiblity of `f` being unset (null) because of the safety contract of `allocate_alarm`.
+                        // - other than that we only store valid function pointers into alarm.callback
+                        let f: fn(*mut ()) = unsafe { mem::transmute(alarm.callback) };
+                        f(alarm.ctx);
+                    } else {
+                        next_alarm = next_alarm.min(alarm.timestamp);
+                    }
+                }
+            }
+
+            let until =
+                unsafe { DRIVER.zero_instant.read() } + StdDuration::from_micros(next_alarm);
+
+            unsafe { DRIVER.signaler.as_ref() }.wait_until(until);
+        }
+    }
+}
+
+impl Driver for TimeDriver {
+    fn now(&self) -> u64 {
+        self.init();
+
+        let zero = unsafe { self.zero_instant.read() };
+        StdInstant::now().duration_since(zero).as_micros() as u64
+    }
+
+    unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
+        let id = self
+            .alarm_count
+            .fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
+                if x < ALARM_COUNT as u8 {
+                    Some(x + 1)
+                } else {
+                    None
+                }
+            });
+
+        match id {
+            Ok(id) => Some(AlarmHandle::new(id)),
+            Err(_) => None,
+        }
+    }
+
+    fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
+        self.init();
+        let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
+        let alarm = &mut alarms[alarm.id() as usize];
+        alarm.callback = callback as *const ();
+        alarm.ctx = ctx;
+    }
+
+    fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) {
+        self.init();
+        let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
+        let alarm = &mut alarms[alarm.id() as usize];
+        alarm.timestamp = timestamp;
+        unsafe { self.signaler.as_ref() }.signal();
+    }
+}
+
+struct Signaler {
+    mutex: Mutex<bool>,
+    condvar: Condvar,
+}
+
+impl Signaler {
+    fn new() -> Self {
+        Self {
+            mutex: Mutex::new(false),
+            condvar: Condvar::new(),
+        }
+    }
+
+    fn wait_until(&self, until: StdInstant) {
+        let mut signaled = self.mutex.lock().unwrap();
+        while !*signaled {
+            let now = StdInstant::now();
+
+            if now >= until {
+                break;
+            }
+
+            let dur = until - now;
+            let (signaled2, timeout) = self.condvar.wait_timeout(signaled, dur).unwrap();
+            signaled = signaled2;
+            if timeout.timed_out() {
+                break;
+            }
+        }
+        *signaled = false;
+    }
+
+    fn signal(&self) {
+        let mut signaled = self.mutex.lock().unwrap();
+        *signaled = true;
+        self.condvar.notify_one();
+    }
+}
+
+pub(crate) struct UninitCell<T>(MaybeUninit<UnsafeCell<T>>);
+unsafe impl<T> Send for UninitCell<T> {}
+unsafe impl<T> Sync for UninitCell<T> {}
+
+impl<T> UninitCell<T> {
+    pub const fn uninit() -> Self {
+        Self(MaybeUninit::uninit())
+    }
+
+    pub unsafe fn as_ptr(&self) -> *const T {
+        (*self.0.as_ptr()).get()
+    }
+
+    pub unsafe fn as_mut_ptr(&self) -> *mut T {
+        (*self.0.as_ptr()).get()
+    }
+
+    pub unsafe fn as_ref(&self) -> &T {
+        &*self.as_ptr()
+    }
+
+    pub unsafe fn write(&self, val: T) {
+        ptr::write(self.as_mut_ptr(), val)
+    }
+}
+
+impl<T: Copy> UninitCell<T> {
+    pub unsafe fn read(&self) -> T {
+        ptr::read(self.as_mut_ptr())
+    }
+}
diff --git a/embassy/src/time/mod.rs b/embassy/src/time/mod.rs
index db48fb3ec..e50742040 100644
--- a/embassy/src/time/mod.rs
+++ b/embassy/src/time/mod.rs
@@ -46,6 +46,9 @@ mod duration;
 mod instant;
 mod timer;
 
+#[cfg(feature = "std")]
+mod driver_std;
+
 pub use delay::{block_for, Delay};
 pub use duration::Duration;
 pub use instant::Instant;
diff --git a/examples/std/Cargo.toml b/examples/std/Cargo.toml
index 466814850..34b8ebb67 100644
--- a/examples/std/Cargo.toml
+++ b/examples/std/Cargo.toml
@@ -5,8 +5,7 @@ name = "embassy-std-examples"
 version = "0.1.0"
 
 [dependencies]
-embassy = { version = "0.1.0", path = "../../embassy", features = ["log"] }
-embassy-std = { version = "0.1.0", path = "../../embassy-std" }
+embassy = { version = "0.1.0", path = "../../embassy", features = ["log", "std", "time"] }
 embassy-net = { version = "0.1.0", path = "../../embassy-net", features=["std", "log", "medium-ethernet", "tcp", "dhcpv4"] }
 smoltcp = { git = "https://github.com/smoltcp-rs/smoltcp", rev="e4241510337e095b9d21136c5f58b2eaa1b78479", default-features = false }
 
diff --git a/examples/std/src/bin/net.rs b/examples/std/src/bin/net.rs
index 323d711a8..b98b97090 100644
--- a/examples/std/src/bin/net.rs
+++ b/examples/std/src/bin/net.rs
@@ -2,11 +2,10 @@
 #![allow(incomplete_features)]
 
 use clap::{AppSettings, Clap};
-use embassy::executor::Spawner;
+use embassy::executor::{Executor, Spawner};
 use embassy::io::AsyncWriteExt;
 use embassy::util::Forever;
 use embassy_net::*;
-use embassy_std::Executor;
 use heapless::Vec;
 use log::*;
 
diff --git a/examples/std/src/bin/serial.rs b/examples/std/src/bin/serial.rs
index ca596a34c..181c5dfaa 100644
--- a/examples/std/src/bin/serial.rs
+++ b/examples/std/src/bin/serial.rs
@@ -5,9 +5,9 @@
 mod serial_port;
 
 use async_io::Async;
+use embassy::executor::Executor;
 use embassy::io::AsyncBufReadExt;
 use embassy::util::Forever;
-use embassy_std::Executor;
 use log::*;
 use nix::sys::termios;
 
diff --git a/examples/std/src/bin/tick.rs b/examples/std/src/bin/tick.rs
index 16f54b2c6..385b317d4 100644
--- a/examples/std/src/bin/tick.rs
+++ b/examples/std/src/bin/tick.rs
@@ -1,9 +1,9 @@
 #![feature(type_alias_impl_trait)]
 #![allow(incomplete_features)]
 
+use embassy::executor::Executor;
 use embassy::time::{Duration, Timer};
 use embassy::util::Forever;
-use embassy_std::Executor;
 use log::*;
 
 #[embassy::task]