Implement power-efficient sleep after boot-up

* arch-based crates, inspired by Redox
* Do not burn cpu uselessly.
* Start using cortex-a registers.
* Important: initialise stack pointer!

Cargo.lock

@@ -26,6 +26,14 @@ dependencies = [
  "rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "cortex-a"
+version = "3.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "register 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "nodrop"
 version = "0.1.14"
@@ -44,6 +52,14 @@ name = "r0"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "register"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "tock-registers 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "rlibc"
 version = "1.0.0"
@@ -70,6 +86,11 @@ name = "semver-parser"
 version = "0.7.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "tock-registers"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "ux"
 version = "0.1.3"
@@ -79,6 +100,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "vesper"
 version = "0.0.1"
 dependencies = [
+ "cortex-a 3.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "qemu-exit 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "r0 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rlibc 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -101,12 +123,15 @@ dependencies = [
 "checksum bit_field 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ed8765909f9009617974ab6b7d332625b320b33c326b1e9321382ef1999b5d56"
 "checksum bitflags 1.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 "checksum cast 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "4b9434b9a5aa1450faa3f9cb14ea0e8c53bb5d2b3c1bfd1ab4fc03e9f33fbfb0"
+"checksum cortex-a 3.0.4 (registry+https://github.com/rust-lang/crates.io-index)" = "6922a40af4d1a2deac8c963b9f3e57311b8912490740234f1ad182425c547f80"
 "checksum nodrop 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
 "checksum qemu-exit 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "95533662c327a4b3be4203123662b7eca1c39d73d66020c52280e4ff0e9c9a41"
 "checksum r0 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e2a38df5b15c8d5c7e8654189744d8e396bddc18ad48041a500ce52d6948941f"
+"checksum register 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "deaba5b0e477d21f61a57504bb5cef4a1e86de30300b457d38971c1cfc98b815"
 "checksum rlibc 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc874b127765f014d792f16763a81245ab80500e2ad921ed4ee9e82481ee08fe"
 "checksum rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
+"checksum tock-registers 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "70323afdb8082186c0986da0e10f6e4ed103d681c921c00597e98d9806dac20f"
 "checksum ux 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "88dfeb711b61ce620c0cb6fd9f8e3e678622f0c971da2a63c4b3e25e88ed012f"
 "checksum x86_64 0.7.7 (registry+https://github.com/rust-lang/crates.io-index)" = "1f27d9168654aee1b0c1b73746caeb4aa33248f8b8c8f6e100e697fcc2a794b2"

linker/aarch64.ld

@@ -4,7 +4,7 @@
  * Original code distributed under MIT, additional changes are under BlueOak-1.0.0
  */
 
-ENTRY(_boot_cores);
+ENTRY(karch_start);
 
 /* Symbols between __boot_start and __boot_end should be dropped after init is complete.
    Symbols between __ro_start and __ro_end are the kernel code.

nucleus/Cargo.toml

@@ -23,3 +23,4 @@ qemu = ["qemu-exit"]
 r0 = "0.2"
 rlibc = "1.0"
 qemu-exit = { version = "0.1", optional = true }
+cortex-a = "3.0"

nucleus/src/arch/README.md

@@ -0,0 +1,5 @@
+# Architecture-specific code
+
+This directory contains code specific to a certain architecture.
+
+Implementations of arch-specific kernel calls are also placed here.

nucleus/src/arch/aarch64/mod.rs

@@ -0,0 +1,36 @@
+use {
+    crate::kmain,
+    cortex_a::{
+        asm,
+        regs::{RegisterReadOnly, RegisterReadWrite, MPIDR_EL1, SP},
+    },
+};
+
+/// The entry to Rust, all things must be initialized
+/// This is invoked from the linker script, does arch-specific init
+/// and passes control to the kernel boot function kmain().
+#[no_mangle]
+pub unsafe extern "C" fn karch_start() -> ! {
+    // Set sp to 0x80000 (just before kernel start)
+    const STACK_START: u64 = 0x8_0000;
+
+    SP.set(STACK_START);
+
+    match read_cpu_id() {
+        0 => kmain(),
+        _ => endless_sleep(), // if not core0, indefinitely wait for events
+    }
+}
+
+#[inline]
+pub fn read_cpu_id() -> u64 {
+    const CORE_MASK: u64 = 0x3;
+    MPIDR_EL1.get() & CORE_MASK
+}
+
+#[inline]
+pub fn endless_sleep() -> ! {
+    loop {
+        asm::wfe();
+    }
+}

nucleus/src/arch/mod.rs

@@ -0,0 +1,5 @@
+#[cfg(target_arch = "aarch64")]
+#[macro_use]
+pub mod aarch64;
+#[cfg(target_arch = "aarch64")]
+pub use self::aarch64::*;

nucleus/src/main.rs

@@ -1,12 +1,20 @@
 #![no_std]
 #![no_main]
 
-#[no_mangle]
+#[cfg(not(target_arch = "aarch64"))]
-pub extern "C" fn _boot_cores() -> ! {
+use architecture_not_supported_sorry;
-    loop {}
+
+#[macro_use]
+pub mod arch;
+pub use arch::*;
+
+// Kernel entry point
+// arch crate is responsible for calling this
+pub fn kmain() -> ! {
+    endless_sleep()
 }
 
 #[panic_handler]
 fn panicked(_info: &core::panic::PanicInfo) -> ! {
-    loop {}
+    endless_sleep()
 }