alt_alarm_start.c

nios中自定义指令集实现三角函数的软件部分。

/******************************************************************************
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* License Agreement                                                           *
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* Copyright (c) 2004 Altera Corporation, San Jose, California, USA.           *
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/******************************************************************************
*                                                                             *
* THIS IS A LIBRARY READ-ONLY SOURCE FILE. DO NOT EDIT IT DIRECTLY.           *
*                                                                             *
* Overriding HAL Functions                                                    *
*                                                                             *
* To provide your own implementation of a HAL function, include the file in   *
* your Nios II IDE application project. When building the executable, the     *
* Nios II IDE finds your function first, and uses it in place of the HAL      *
* version.                                                                    *
*                                                                             *
******************************************************************************/

#include <errno.h>

#include "sys/alt_alarm.h"
#include "sys/alt_irq.h"

/*
 * alt_alarm_start is called to register an alarm with the system. The 
 * "alarm" structure passed as an input argument does not need to be 
 * initialised by the user. This is done within this function.
 *
 * The remaining input arguments are:
 *
 * nticks - The time to elapse until the alarm executes. This is specified in
 *          system clock ticks.
 * callback - The function to run when the indicated time has elapsed.
 * context  - An opaque value, passed to the callback function. 
*
 * Care should be taken when defining the callback function since it is 
 * likely to execute in interrupt context. In particular, this mean that 
 * library calls like printf() should not be made, since they can result in 
 * deadlock.
 *
 * The interval to be used for the next callback is the return
 * value from the callback function. A return value of zero indicates that the
 * alarm should be unregistered. 
 * 
 * alt_alarm_start() will fail if  the timer facility has not been enabled 
 * (i.e. there is no system clock). Failure is indicated by a negative return 
 * value.
 */ 

int alt_alarm_start (alt_alarm* alarm, alt_u32 nticks,
                     alt_u32 (*callback) (void* context),
                     void* context)
{
  alt_irq_context irq_context;
  alt_u32 current_nticks = 0;
  
  if (alt_ticks_per_second ())
  {
    if (alarm)
    {
      alarm->callback = callback;
      alarm->context  = context;
 
      irq_context = alt_irq_disable_all ();
      
      current_nticks = alt_nticks();
      
      alarm->time = nticks + current_nticks + 1; 
      
      /* 
       * If the desired alarm time causes a roll-over, set the rollover
       * flag. This will prevent the subsequent tick event from causing
       * an alarm too early.
       */
      if(alarm->time < current_nticks)
      {
        alarm->rollover = 1;
      }
      else
      {
        alarm->rollover = 0;
      }
    
      alt_llist_insert (&alt_alarm_list, &alarm->llist);
      alt_irq_enable_all (irq_context);

      return 0;
    }
    else
    {
      return -EINVAL;
    }
  }
  else
  {
    return -ENOTSUP;
  }
}