5.3.1.2.9. sys_lock

Pure userspace semaphore, as proposed in libstd.h, do not permit easy handling of variable shared between ISR and main threads. ISR treatments do not allow to sleep or wait for the main thread to release semaphores. The solution to this problem is to instruct Ewok not to schedule the ISR routine while the shared variable is in use in the main thread. Of course such a situation ought to be short.

Contents

• sys_lock
  • sys_lock()

5.3.1.2.9.1. sys_lock()

sys_lock: postpone the ISR while a lock is set by the main thread. This efficiently creates a critical section in the main thread with respect to the ISR thread.

Note

Synchronous syscall, executable in main thread mode only

In EwoK, all tasks main threads can lock one of their variables without requesting any specific permission.

The lock syscall has the following API:

e_syscall_ret sys_lock(LOCK_ENTER);
e_syscall_ret sys_lock(LOCK_EXIT);

Warning

Locking the task should be done for a very short amount of time, as associated ISR are postponed, which may generate big slowdown on the associated devices performance.