add os[1-8]-ref for os refereces, add guide, add README

os8-ref/src/timer.rs

@@ -0,0 +1,83 @@
+//! RISC-V timer-related functionality
+
+use crate::config::CLOCK_FREQ;
+use crate::sbi::set_timer;
+use crate::sync::UPSafeCell;
+use crate::task::{add_task, TaskControlBlock};
+use alloc::collections::BinaryHeap;
+use alloc::sync::Arc;
+use core::cmp::Ordering;
+use lazy_static::*;
+use riscv::register::time;
+
+const TICKS_PER_SEC: usize = 100;
+const MILLI_PER_SEC: usize = 1_000;
+const MICRO_PER_SEC: usize = 1_000_000;
+
+/// read the `mtime` register
+pub fn get_time() -> usize {
+    time::read()
+}
+
+/// get current time in microseconds
+pub fn get_time_us() -> usize {
+    time::read() / (CLOCK_FREQ / MICRO_PER_SEC)
+}
+
+/// get current time in milliseconds
+pub fn get_time_ms() -> usize {
+    time::read() / (CLOCK_FREQ / MILLI_PER_SEC)
+}
+
+/// set the next timer interrupt
+pub fn set_next_trigger() {
+    set_timer(get_time() + CLOCK_FREQ / TICKS_PER_SEC);
+}
+
+pub struct TimerCondVar {
+    pub expire_ms: usize,
+    pub task: Arc<TaskControlBlock>,
+}
+
+impl PartialEq for TimerCondVar {
+    fn eq(&self, other: &Self) -> bool {
+        self.expire_ms == other.expire_ms
+    }
+}
+impl Eq for TimerCondVar {}
+impl PartialOrd for TimerCondVar {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        let a = -(self.expire_ms as isize);
+        let b = -(other.expire_ms as isize);
+        Some(a.cmp(&b))
+    }
+}
+
+impl Ord for TimerCondVar {
+    fn cmp(&self, other: &Self) -> Ordering {
+        self.partial_cmp(other).unwrap()
+    }
+}
+
+lazy_static! {
+    static ref TIMERS: UPSafeCell<BinaryHeap<TimerCondVar>> =
+        unsafe { UPSafeCell::new(BinaryHeap::<TimerCondVar>::new()) };
+}
+
+pub fn add_timer(expire_ms: usize, task: Arc<TaskControlBlock>) {
+    let mut timers = TIMERS.exclusive_access();
+    timers.push(TimerCondVar { expire_ms, task });
+}
+
+pub fn check_timer() {
+    let current_ms = get_time_ms();
+    let mut timers = TIMERS.exclusive_access();
+    while let Some(timer) = timers.peek() {
+        if timer.expire_ms <= current_ms {
+            add_task(Arc::clone(&timer.task));
+            timers.pop();
+        } else {
+            break;
+        }
+    }
+}