message: Clarify "driver_check" doc since it only checks for presence
diff: @@ -21,9 +21,11 @@ use libtock_platform::Syscalls;
  pub struct LowLevelDebug<S: Syscalls>(S);
  impl<S: Syscalls> LowLevelDebug<S> {
  - /// Run a check against the low-level debug capsule to ensure it is working.
  + /// Run a check against the low-level debug capsule to ensure it is present.
  ///
  - /// Returns `true` if the driver was present and functional.
  + /// Returns `true` if the driver was present. This does not necessarily mean
  + /// that the driver is working, as it may still fail to allocate grant
  + /// memory.
  #[inline(always)]
  pub fn driver_check() -> bool {
  S::command(DRIVER_ID, DRIVER_CHECK, 0, 0).is_success()
  