/*
* task.c
* ----------------
* Simple cooperative tasking system.
*
* Copyright (c) 2017, NORDUnet A/S All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
* - Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of the NORDUnet nor the names of its contributors may
* be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
* PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
* TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
/* Dead-simple fully-cooperative tasker. There are no priorities; tasks
* are run in a strictly round-robin fashion. There is no preemption;
* tasks explicitly yield control. Tasks are created at system init time,
* and are expected to run an infinite loop; tasks do not return, nor are
* tasks deleted.
*/
#include "stm-init.h"
#include "task.h"
/* Task Control Block. The structure is private, in case we want to change
* it later without having to change the API. In any case, external code
* shouldn't poke its fingers in the internal details.
*/
struct task_cb {
struct task_cb *next;
task_state_t state;
char *name;
funcp_t func;
void *cookie;
void *stack_base;
size_t stack_len;
void *stack_ptr;
};
/* Number of tasks. Default is number of RPC dispatch tasks, plus CLI task. */
#ifndef MAX_TASK
#ifdef NUM_RPC_TASK
#define MAX_TASK (NUM_RPC_TASK + 2)
#else
#define MAX_TASK 6
#endif
#endif
static tcb_t tcbs[MAX_TASK];
static size_t num_task = 0;
/* We have a circular list of tasks. New tasks are added at the tail, and
* tail->next is the head.
*/
static tcb_t *tail = NULL;
/* Currently running task */
static tcb_t *cur_task = NULL;
#define STACK_GUARD_WORD 0x55AA5A5A
/* Add a task.
*/
tcb_t *task_add(char *name, funcp_t func, void *cookie, void *stack, size_t stack_len)
{
if (num_task >= MAX_TASK)
return NULL;
if (name == NULL || func == NULL || stack == NULL)
return NULL;
tcb_t *t = &tcbs[num_task++];
t->state = TASK_INIT;
t->name = name;
t->func = func;
t->cookie = cookie;
t->stack_base = stack;
t->stack_len = stack_len;
t->stack_ptr = stack + stack_len;
for (uint32_t *p = (uint32_t *)t->stack_base; p < (uint32_t *)t->stack_ptr; ++p)
*p = STACK_GUARD_WORD;
if (tail == NULL) {
/* Empty list; initialize it to this task. */
t->next = t;
}
else {
/* Otherwise insert at the end of the list. */
t->next = tail->next;
tail->next = t;
}
tail = t;
return t;
}
/* Set the idle hook function pointer.
*
* This function is called repeatedly when the system is idle (there are
* no runnable tasks).
*
* The idle function should NOT call task_delay or HAL_Delay, because that
* will cause fatal recursion. We could add a recursion guard to
* task_yield, but we're not currently using the idle hook, and I'm
* thinking about removing it entirely.
*/
static void default_idle_hook(void) { }
static funcp_t idle_hook = default_idle_hook;
void task_set_idle_hook(funcp_t func)
{
idle_hook = (func == NULL) ? default_idle_hook : func;
}
/* Find the next runnable task.
*/
static tcb_t *next_task(void)
{
tcb_t *t;
/* If the tasker isn't running yet, return the first task. */
if (cur_task == NULL)
return (tail == NULL) ? NULL : tail->next;
// XXX critical section?
/* find the next runnable task */
for (t = cur_task->next; t != cur_task; t = t->next) {
if (t->state != TASK_WAITING)
return t;
}
/* searched all the way back to cur_task - is it runnable? */
return (cur_task->state == TASK_WAITING) ? NULL : cur_task;
}
/* Check for stack overruns.
*/
static void check_stack(tcb_t *t)
{
if (t->stack_ptr < t->stack_base ||
t->stack_ptr >= t->stack_base + t->stack_len ||
*(uint32_t *)t->stack_base != STACK_GUARD_WORD)
Error_Handler();
}
/* Yield control to the next runnable task.
*/
void task_yield(void)
{
tcb_t *next;
/* If there are no defined tasks, exit immediately so we don't get
* caught in the idle loop.
*/
if (tail == NULL)
return;
/* Find the next runnable task. Loop if every task is waiting. */
while (1) {
next = next_task();
if (next == NULL)
idle_hook();
else
break;
}
/* If we decide we don't need the idle hook, the preceding loop could
* devolve to something like this:
*
* do {
* next = next_task();
* } while (next == NULL);
*/
/* If there are no other runnable tasks (and cur_task is runnable),
* we don't need to context-switch.
*/
if (next == cur_task)
return;
/* Save current context, if there is one. */
if (cur_task != NULL) {
__asm("push {r0-r12, lr}");
cur_task->stack_ptr = (void *)__get_MSP();
/* Check for stack overruns. */
check_stack(cur_task);
}
cur_task = next;
/* If task is in init state, call its entry point. */
if (cur_task->state == TASK_INIT) {
__set_MSP((uint32_t)cur_task->stack_ptr);
cur_task->state = TASK_READY;
cur_task->func();
/*NOTREACHED*/
}
/* Otherwise, restore the task's context. */
else {
__set_MSP((uint32_t)cur_task->stack_ptr);
__asm("pop {r0-r12, lr}");
return;
}
}
/* Put the current task to sleep (make it non-runnable).
*/
void task_sleep(void)
{
if (cur_task != NULL)
cur_task->state = TASK_WAITING;
task_yield();
}
/* Wake a task (make it runnable).
*/
void task_wake(tcb_t *t)
{
if (t != NULL)
t->state = TASK_READY;
}
/* Accessor functions */
tcb_t *task_get_tcb(void)
{
return cur_task;
}
char *task_get_name(tcb_t *t)
{
if (t == NULL)
t = cur_task;
return t->name;
}
funcp_t task_get_func(tcb_t *t)
{
if (t == NULL)
t = cur_task;
return t->func;
}
void *task_get_cookie(tcb_t *t)
{
if (t == NULL)
t = cur_task;
return t->cookie;
}
task_state_t task_get_state(tcb_t *t)
{
if (t == NULL)
t = cur_task;
return t->state;
}
void *task_get_stack(tcb_t *t)
{
if (t == NULL)
t = cur_task;
return t->stack_ptr;
}
/* stupid linear search for first non guard word */
size_t task_get_stack_highwater(tcb_t *t)
{
if (t == NULL)
t = cur_task;
const uint32_t * const b = (uint32_t *)t->stack_base;
for (size_t i = 0; i < t->stack_len/4; ++i) {
if (b[i] != STACK_GUARD_WORD) {
return (t->stack_len - (i * 4));
}
}
return 0;
}
/* Iterate through tasks.
*
* Returns the next task control block, or NULL at the end of the list.
*/
tcb_t *task_iterate(tcb_t *t)
{
if (t == NULL)
return (tail == NULL) ? NULL : tail->next;
if (t == tail)
return NULL;
return t->next;
}
/* Delay a number of 1ms ticks.
*/
void task_delay(uint32_t delay)
{
uint32_t tickstart = HAL_GetTick();
while ((HAL_GetTick() - tickstart) < delay)
task_yield();
}
void HAL_Delay(uint32_t delay) __attribute__((alias("task_delay")));
/* Simple mutex-like locks. A real mutex would require the unlocker to be
* the current owner, but then we have to define and return errors, when
* all we want at the moment is simple mutual exclusion.
*/
void task_mutex_lock(task_mutex_t *mutex)
{
while (mutex->locked)
task_yield();
mutex->locked = 1;
}
void task_mutex_unlock(task_mutex_t *mutex)
{
if (mutex != NULL)
mutex->locked = 0;
}
