add feature gate for nightly and no_std

Cargo.toml

@@ -13,6 +13,12 @@ license = "MIT/Apache-2.0"
 edition = '2021'
 exclude = ["/.gitlab-ci.yml", ".gitignore", ".gitattributes", "/.github/*"]
 
+[features]
+default = ["nightly", "no_std"]
+nightly = ["asm_const"]
+asm_const = []
+no_std = []
+
 [dependencies]
 aarch64-cpu = { version = "9.3" }
 tock-registers = { version = "0.8.x", default-features = false }

src/instructions.rs

@@ -6,6 +6,7 @@ pub fn halt() {
     unsafe { asm!("wfi", options(nomem, nostack)) }
 }
 
+#[cfg(asm_const)]
 mod exceptions {
     use core::arch::asm;
 

src/lib.rs

@@ -7,7 +7,7 @@
 
 #![allow(dead_code)]
 #![allow(stable_features)]
-#![feature(asm_const, core_intrinsics)]
+#![cfg_attr(feature = "asm_const", feature(asm_const))]
 #![no_std]
 
 pub mod instructions;

src/paging.rs

@@ -1,3 +1,4 @@
+#[cfg(no_std)]
 use core::convert::{From, Into};
 use core::fmt;
 use core::ops;