/* Einkornix, a tiny, primitive cooperative-multitasking operating
   system for the ARM EABI, which consists of 34 instructions of
   Thumb-2 code (84 bytes) and 4 bytes of data, plus 8 bytes per
   thread, plus the thread stacks.  The implementation is in
   einkornix.S.  Documentation is below, or see einkornix-test.c for
   example usage.  Relatedly, monokokko.S is a cut-down all-assembly
   version not compatible with the standard ABI. */

/* An Einkornix thread is called a task.  This struct stores its
   state: */
typedef struct eintask {
  void *stack;
  struct eintask *next;
} eintask;

/* Call einstart initially to create a task list consisting of a
   single task, the current one, initializing an uninitialized
   eintask in the process: */
void einstart(eintask *me);

/* Call to start a new task; first you must allocate kid and
   initialize kid->stack to point to an 8-byte-aligned location at the
   end of its stack space (which you must also allocate).  start is
   the function to invoke initially in the new task, passing it
   argument userdata.  start must not return. */
void einspawn(eintask *kid, void (*start)(void *userdata), void *userdata);

/* Call from a task to yield the CPU to other tasks. */
void einyield(void);

/* Call from a task to terminate it.  Does not return.  If you want to
   reclaim the task's eintask struct or stack space for reuse, you'll
   need to keep track of it in your own code. */
void einexit(void);