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+/************************************************************
+ * sched_setparam.c
+ *
+ * Copyright (C) 2007 Gregory Nutt. All rights reserved.
+ * Author: Gregory Nutt <spudmonkey@racsa.co.cr>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. 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.
+ * 3. Neither the name Gregory Nutt 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 OWNER 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.
+ *
+ ************************************************************/
+
+/************************************************************
+ * Included Files
+ ************************************************************/
+
+#include <nuttx/config.h>
+#include <sys/types.h>
+#include <sched.h>
+#include <nuttx/arch.h>
+#include <nuttx/os_external.h>
+#include "os_internal.h"
+
+/************************************************************
+ * Definitions
+ ************************************************************/
+
+/************************************************************
+ * Private Type Declarations
+ ************************************************************/
+
+/************************************************************
+ * Global Variables
+ ************************************************************/
+
+/************************************************************
+ * Private Variables
+ ************************************************************/
+
+/************************************************************
+ * Private Function Prototypes
+ ************************************************************/
+
+/************************************************************
+ * Private Functions
+ ************************************************************/
+
+/************************************************************
+ * Public Functions
+ ************************************************************/
+
+/************************************************************
+ * Name: sched_setparam
+ *
+ * Description:
+ * This function sets the priority of a specified task.
+ *
+ * NOTE: Setting a task's priority to the same value has the
+ * similar effect to sched_yield() -- The task will be moved to
+ * after all other tasks with the same priority.
+ *
+ * Inputs:
+ * pid - the task ID of the task to reprioritize. If pid is
+ * zero, the priority of the calling task is changed.
+ * param - A structure whose member sched_priority is the integer
+ * priority. The range of valid priority numbers is from
+ * SCHED_PRIORITY_MIN through SCHED_PRIORITY_MAX.
+ *
+ * Return Value:
+ * OK if successful, otherwise ERROR. This function can
+ * fail for the following reasons:
+ *
+ * (1) parm is NULL or parm->sched_priority is out of
+ * range.
+ * (2) pid does not correspond to any task.
+ *
+ * (errno is not set).
+ *
+ * Assumptions:
+ *
+ ************************************************************/
+
+int sched_setparam(pid_t pid, const struct sched_param *param)
+{
+ _TCB *rtcb;
+ _TCB *tcb;
+ tstate_t task_state;
+ uint32 saved_state;
+ int sched_priority = param->sched_priority;
+ int ret = 0;
+
+ /* Verify that the requested priority is in the valid range */
+
+ if (!param ||
+ param->sched_priority < SCHED_PRIORITY_MIN ||
+ param->sched_priority > SCHED_PRIORITY_MAX)
+ {
+ return ERROR;
+ }
+
+ /* Prohibit modifications to the head of the ready-to-run task
+ * list while adjusting the priority
+ */
+
+ sched_lock();
+
+ /* Check if the task to reprioritize is the calling task */
+
+ rtcb = (_TCB*)g_readytorun.head;
+ if (pid == 0 || pid == rtcb->pid)
+ {
+ tcb = rtcb;
+ }
+
+ /* The pid is not the calling task, we will have to search for it */
+
+ else
+ {
+ tcb = sched_gettcb(pid);
+ if (!tcb)
+ {
+ /* No task with this pid was found */
+
+ sched_unlock();
+ return ERROR;
+ }
+ }
+
+ /* We need to assure that there there is no interrupt activity while
+ * performing the following.
+ */
+
+ saved_state = irqsave();
+
+ /* There are four cases that must be considered: */
+
+ task_state = tcb->task_state;
+ switch (task_state)
+ {
+ /* CASE 1. The task is running or ready-to-run and a context switch
+ * may be caused by the re-prioritization
+ */
+
+ case TSTATE_TASK_RUNNING:
+
+ /* A context switch will occur if the new priority of the running
+ * task becomes less than OR EQUAL TO the next highest priority
+ * ready to run task.
+ */
+
+ if (sched_priority <= tcb->flink->sched_priority)
+ {
+ /* A context switch will occur. */
+
+ up_reprioritize_rtr(tcb, (ubyte)sched_priority);
+ }
+
+ /* Otherwise, we can just change priority since it has no effect */
+
+ else
+ {
+ /* Change the task priority */
+
+ tcb->sched_priority = (ubyte)sched_priority;
+ }
+ break;
+
+ /* CASE 2. The task is running or ready-to-run and a context switch
+ * may be caused by the re-prioritization
+ */
+
+ case TSTATE_TASK_READYTORUN:
+
+ /* A context switch will occur if the new priority of the ready-to
+ * run task is (strictly) greater than the current running task
+ */
+
+ if (sched_priority > rtcb->sched_priority)
+ {
+ /* A context switch will occur. */
+
+ up_reprioritize_rtr(tcb, (ubyte)sched_priority);
+ }
+
+ /* Otherwise, we can just change priority and re-schedule (since it
+ * have no other effect).
+ */
+
+ else
+ {
+ /* Remove the TCB from the ready-to-run task list */
+
+ ASSERT(!sched_removereadytorun(tcb));
+
+ /* Change the task priority */
+
+ tcb->sched_priority = (ubyte)sched_priority;
+
+ /* Put it back into the ready-to-run task list */
+
+ ASSERT(!sched_addreadytorun(tcb));
+ }
+ break;
+
+ /* CASE 3. The task is not in the ready to run list. Changing its
+ * Priority cannot effect the currently executing task.
+ */
+
+ default:
+ /* CASE 3a. The task resides in a prioritized list. */
+
+ if (g_tasklisttable[task_state].prioritized)
+ {
+ /* Remove the TCB from the prioritized task list */
+
+ dq_rem((dq_entry_t*)tcb, g_tasklisttable[task_state].list);
+
+ /* Change the task priority */
+
+ tcb->sched_priority = (ubyte)sched_priority;
+
+ /* Put it back into the prioritized list at the correct
+ * position
+ */
+
+ sched_addprioritized(tcb, g_tasklisttable[task_state].list);
+ }
+
+ /* CASE 3b. The task resides in a non-prioritized list. */
+
+ else
+ {
+ /* Just change the task's priority */
+
+ tcb->sched_priority = (ubyte)sched_priority;
+ }
+ break;
+ }
+
+ irqrestore(saved_state);
+ sched_unlock();
+ return ret;
+}
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