Merge pull request #10 from ian-h-chamberlain/gettime/monotonic

Impl `clock_gettime` for `CLOCK_MONOTONIC`

src/lib.rs

@@ -1,10 +1,15 @@
 #![no_std]
 
+use core::convert::TryFrom;
 use core::mem::MaybeUninit;
 use core::ptr;
 
 extern crate libc;
 
+// avoid conflicting a real POSIX errno by using a value < 0
+// should we define this in ctru-sys somewhere or something?
+const ECTRU: libc::c_int = -1;
+
 /// Call this somewhere to force Rust to link this module.
 /// The call doesn't need to execute, just exist.
 ///
@@ -51,6 +56,7 @@ unsafe extern "C" fn clock_gettime(
     tp: *mut libc::timespec,
 ) -> libc::c_int {
     let mut retval = -1;
+
     match clock_id {
         libc::CLOCK_REALTIME => {
             let mut tv = MaybeUninit::uninit();
@@ -62,6 +68,24 @@ unsafe extern "C" fn clock_gettime(
                 (*tp).tv_sec = tv.tv_sec;
             }
         }
+        libc::CLOCK_MONOTONIC => {
+            if let Ok(tick) = i64::try_from(ctru_sys::svcGetSystemTick()) {
+                retval = 0;
+
+                let sysclock_rate = i64::from(ctru_sys::SYSCLOCK_ARM11);
+                (*tp).tv_sec = tick / sysclock_rate;
+
+                // this should always fit in an f64 easily, since it's < sysclock_rate
+                let remainder = (tick % sysclock_rate) as f64;
+
+                // cast to i32 rounds toward zero, which should be fine for this use case
+                (*tp).tv_nsec = (1000.0 * (remainder / ctru_sys::CPU_TICKS_PER_USEC)) as i32;
+            } else {
+                // Too many ticks, this device has been on for >1000 years!
+                // We would have otherwise given a negative result back to caller
+                *__errno() = ECTRU
+            }
+        }
         _ => *__errno() = libc::EINVAL,
     }