Comment APIs for current task.

src/task/current.rs

@@ -1,9 +1,18 @@
 use crate::{config, interrupt::svc, schedule::current};
 
+/// Switch the current task out of the CPU and let the scheduler pick the next
+/// task to run.
 pub fn yield_current() {
     svc::svc_yield_current_task();
 }
 
+/// Change the priority of the currently running task. Return `Ok(())` if the
+/// priority is successfully changed. Return `Err(())` if the given new
+/// priority is not allowed by the configuration settings.
+/// 
+/// If successful, the new priority will have taken effect when the function
+/// returns. If the priority is reduced, any ready task that becomes having a
+/// higher priority than the current task will have preempted the current task.
 pub fn change_current_priority(prio: u8) -> Result<(), ()> {
     if prio >= config::TASK_PRIORITY_LEVELS - 1 {
         return Err(());
@@ -13,6 +22,8 @@ pub fn change_current_priority(prio: u8) -> Result<(), ()> {
     Ok(())
 }
 
+/// Return the ID of the current task. The ID is only for diagnostic purpose
+/// and does not have any functional purpose.
 pub fn get_current_id() -> u8 {
     current::with_current_task(|cur_task| cur_task.get_id())
 }