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Diffstat (limited to 'task.c')
| -rw-r--r-- | task.c | 318 |
1 files changed, 318 insertions, 0 deletions
@@ -0,0 +1,318 @@ +/* + * 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; + tail = 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). + */ +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; + + /* 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; +} |