Time (#11)

* WIP: Time syscalls

* Count time from PIT using low tickrate

* Implement realtime

* Implement nanosleep with a tight loop

kernel/syscall/time.rs

@@ -0,0 +1,50 @@
+use arch;
+use context;
+use syscall::data::TimeSpec;
+use syscall::error::*;
+use syscall::flag::{CLOCK_REALTIME, CLOCK_MONOTONIC};
+
+pub fn clock_gettime(clock: usize, time: &mut TimeSpec) -> Result<usize> {
+    match clock {
+        CLOCK_REALTIME => {
+            let arch_time = arch::time::realtime();
+            time.tv_sec = arch_time.0 as i64;
+            time.tv_nsec = arch_time.1 as i32;
+            Ok(0)
+        },
+        CLOCK_MONOTONIC => {
+            let arch_time = arch::time::monotonic();
+            time.tv_sec = arch_time.0 as i64;
+            time.tv_nsec = arch_time.1 as i32;
+            Ok(0)
+        },
+        _ => Err(Error::new(EINVAL))
+    }
+}
+
+pub fn nanosleep(req: &TimeSpec, rem_opt: Option<&mut TimeSpec>) -> Result<usize> {
+    let start = arch::time::monotonic();
+    let sum = start.1 + req.tv_nsec as u64;
+    let end = (start.0 + req.tv_sec as u64 + sum / 1000000000, sum % 1000000000);
+    
+    loop {
+        unsafe { context::switch(); }
+
+        let current = arch::time::monotonic();
+        if current.0 > end.0 || (current.0 == end.0 && current.1 >= end.1) {
+            break;
+        }
+    }
+
+    if let Some(mut rem) = rem_opt {
+        rem.tv_sec = 0;
+        rem.tv_nsec = 0;
+    }
+
+    Ok(0)
+}
+
+pub fn sched_yield() -> Result<usize> {
+    unsafe { context::switch(); }
+    Ok(0)
+}