Add embassy-std crate with glue to run embassy on std.

2 files changed, 105 insertions, 0 deletions

diff --git a/embassy-std/Cargo.toml b/embassy-std/Cargo.toml
new file mode 100644
index 000000000..2a8028137
--- /dev/null
+++ b/embassy-std/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "embassy-std"
+version = "0.1.0"
+authors = ["Dario Nieuwenhuis <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+embassy     = { version = "0.1.0", path = "../embassy", features = ["std"] }
+lazy_static = "1.4.0"
+rand_core   = { version = "0.6.0", features = ["std"] }
diff --git a/embassy-std/src/lib.rs b/embassy-std/src/lib.rs
new file mode 100644
index 000000000..2fb814b4d
--- /dev/null
+++ b/embassy-std/src/lib.rs
@@ -0,0 +1,95 @@
+use embassy::executor::Executor;
+use embassy::time::TICKS_PER_SECOND;
+use embassy::time::{Alarm, Clock};
+use embassy::util::Forever;
+use rand_core::{OsRng, RngCore};
+use std::mem::MaybeUninit;
+use std::sync::{Condvar, Mutex};
+use std::time::{Duration as StdDuration, Instant as StdInstant};
+
+static mut CLOCK_ZERO: MaybeUninit<StdInstant> = MaybeUninit::uninit();
+struct StdClock;
+impl Clock for StdClock {
+    fn now(&self) -> u64 {
+        let zero = unsafe { CLOCK_ZERO.as_ptr().read() };
+        let dur = StdInstant::now().duration_since(zero);
+        dur.as_secs() * (TICKS_PER_SECOND as u64)
+            + (dur.subsec_nanos() as u64) * (TICKS_PER_SECOND as u64) / 1_000_000_000
+    }
+}
+
+struct StdRand;
+impl embassy::rand::Rand for StdRand {
+    fn rand(&self, buf: &mut [u8]) {
+        OsRng.fill_bytes(buf);
+    }
+}
+
+static mut ALARM_AT: u64 = u64::MAX;
+
+pub struct StdAlarm;
+impl Alarm for StdAlarm {
+    fn set_callback(&self, _callback: fn()) {}
+    fn set(&self, timestamp: u64) {
+        unsafe { ALARM_AT = timestamp }
+    }
+
+    fn clear(&self) {
+        unsafe { ALARM_AT = u64::MAX }
+    }
+}
+
+static EXECUTOR: Forever<Executor> = Forever::new();
+
+lazy_static::lazy_static! {
+    static ref MUTEX: Mutex<bool> = Mutex::new(false);
+    static ref CONDVAR: Condvar = Condvar::new();
+}
+
+pub fn init() -> &'static Executor {
+    unsafe {
+        CLOCK_ZERO.as_mut_ptr().write(StdInstant::now());
+        embassy::time::set_clock(&StdClock);
+        embassy::rand::set_rand(&StdRand);
+
+        EXECUTOR.put(Executor::new_with_alarm(&StdAlarm, || {
+            let mut signaled = MUTEX.lock().unwrap();
+            *signaled = true;
+            CONDVAR.notify_one();
+        }))
+    }
+}
+
+pub fn run(executor: &'static Executor) -> ! {
+    unsafe {
+        loop {
+            executor.run();
+
+            let mut signaled = MUTEX.lock().unwrap();
+            while !*signaled {
+                let alarm_at = ALARM_AT;
+                if alarm_at == u64::MAX {
+                    signaled = CONDVAR.wait(signaled).unwrap();
+                } else {
+                    let now = StdClock.now();
+                    if now >= alarm_at {
+                        break;
+                    }
+
+                    let left = alarm_at - now;
+                    let dur = StdDuration::new(
+                        left / (TICKS_PER_SECOND as u64),
+                        (left % (TICKS_PER_SECOND as u64) * 1_000_000_000
+                            / (TICKS_PER_SECOND as u64)) as u32,
+                    );
+                    let (signaled2, timeout) = CONDVAR.wait_timeout(signaled, dur).unwrap();
+                    signaled = signaled2;
+                    if timeout.timed_out() {
+                        break;
+                    }
+                }
+            }
+            *signaled = false;
+        }
+    }
+}