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

embassy/Cargo.toml

@@ -5,7 +5,7 @@ authors = ["Dario Nieuwenhuis <dirbaio@dirbaio.net>"]
 edition = "2018"
 
 [features]
-std = ["futures/std", "rand_core"]
+std = ["futures/std"]
 defmt-trace = []
 defmt-debug = []
 defmt-info = []
@@ -16,9 +16,6 @@ defmt-error = []
 defmt = { version = "0.1.3", optional = true }
 log = { version = "0.4.11", optional = true }
 
-# std-only
-rand_core = { version = "0.5.1", optional = true, features = ["std"] }
-
 cortex-m = "0.6.4"
 futures     = { version = "0.3.5", default-features = false }
 pin-project = { version = "1.0.2", default-features = false }

embassy/src/rand.rs

@@ -4,9 +4,6 @@ pub trait Rand {
     fn rand(&self, buf: &mut [u8]);
 }
 
-#[cfg(feature = "std")]
-static mut RAND: Option<&'static dyn Rand> = Some(&if_std::Rand);
-#[cfg(not(feature = "std"))]
 static mut RAND: Option<&'static dyn Rand> = None;
 
 pub unsafe fn set_rand(rand: &'static dyn Rand) {
@@ -16,15 +13,3 @@ pub unsafe fn set_rand(rand: &'static dyn Rand) {
 pub fn rand(buf: &mut [u8]) {
     unsafe { unwrap!(RAND, "No rand set").rand(buf) }
 }
-
-#[cfg(feature = "std")]
-mod if_std {
-    use rand_core::{OsRng, RngCore};
-
-    pub(crate) struct Rand;
-    impl super::Rand for Rand {
-        fn rand(&self, buf: &mut [u8]) {
-            OsRng.fill_bytes(buf)
-        }
-    }
-}