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        /* wait for preload to take effect here */ 
 
        intUnlock (lockKey);                    /* UNLOCK INTERRUPTS */ 
 
        return (OK); 
        } 
 
    /* connect interrupt handler for the correction timer */ 
 
    (void) intConnect (INUM_TO_IVEC (XXX), sysTimestampInt, NULL); 
 
    /* set the correction timer's interrupt vector to XXX (if necessary) */ 
 
    sysTimestampRunning = TRUE; 
 
    /* set the period of the correction timer (see sysTimestampPeriod()) */ 
    /* set the period of the  counting timer = reset count */ 
 
    /* enable the counting timer here */ 
    /* enable the correction timer here */ 
 
    /* wait for preload to take effect on both timers here */ 
 
    return (OK); 
    } 
 
/*************************************************************************** 
* 
* sysTimestampDisable - disable the timestamp timer 
* 
* This routine disables the timestamp timer.  Interrupts are not disabled. 
* However, the tick counter will not decrement after the timestamp timer 
* is disabled, ensuring that interrupts are no longer generated. 
* 
* RETURNS: OK, or ERROR if the timestamp timer cannot be disabled. 
*/ 
  
STATUS sysTimestampDisable (void) 
    { 
    if (sysTimestampRunning) 
        { 
        sysTimestampRunning = FALSE; 
 
        /* disable the correction timer here */ 
        /* disable the counting timer here */ 
        } 
  
    return (OK); 
    } 
 
/*************************************************************************** 
* sysTimestampPeriod - get the timestamp timer period 
* 
* This routine returns the period of the timer in timestamp ticks. 
* The period, or terminal count, is the number of ticks to which the 
* timestamp timer counts before rolling over and restarting the counting 
* process. 
* 
* RETURNS: The period of the timer in timestamp ticks. 
*/ 
  
UINT32 sysTimestampPeriod (void) 
    { 
    /* 
     * Return the correction timer period here. 
     * A reasonable correction period should be chosen.  A short period 
     * causes increased CPU overhead due to correction timer interrupts. 
     * A long period allows for a large accumulation of time skew 
     * due to sysTimestamp() calls stopping the counting timer. 
     */ 
 
    return (TS_CORRECTION_PERIOD); 
    } 
 
/*************************************************************************** 
* sysTimestampFreq - get the timestamp timer clock frequency 
* 
* This routine returns the frequency of the timer clock, in ticks per second. 
* The rate of the timestamp timer should be set explicitly in the BSP, 
* in the sysHwInit() routine. 
* 
* RETURNS: The timestamp timer clock frequency, in ticks per second. 
*/ 
  
UINT32 sysTimestampFreq (void) 
    { 
    UINT32 timerFreq; 
 
    /* 
     * Return the timestamp tick output frequency here. 
     * This value can be determined from the following equation: 
     *     timerFreq = clock input frequency / prescaler  
     *  
     * When possible, read the clock input frequency and prescaler values  
     * directly from chip registers.  
     */   
 
    return (timerFreq); 
    } 
 
/*************************************************************************** 
* 
* sysTimestamp - get the timestamp timer tick count 
* 
* This routine returns the current value of the timestamp timer tick counter. 
* The tick count can be converted to seconds by dividing by the return of 
* sysTimestampFreq(). 
* 
* Call this routine with interrupts locked.  If interrupts are 
* not already locked, use sysTimestampLock() instead. 
* 
* RETURNS: The current timestamp timer tick count. 
* 
* SEE ALSO: sysTimestampLock() 
*/ 
  
UINT32 sysTimestamp (void) 
    { 
    UINT32 tick = 0; 
    register UINT32 * pTick; 
    register UINT32 * pPreload; 
 
    if (sysTimestampRunning) 
        { 
        /* pTick = counter read register location */ 
        /* pPreload = counter preload register location */ 
 
        /* disable counting timer here */ 
 
        tick = *pTick;                  /* read counter value */ 
        *pPreload = tick - TS_SKEW;     /* set preload value  
                                           (with time-skew adjustment) */ 
 
        /* enable counting timer here */ 
 
        tick -= (0xfff...);             /* adjust to incrementing value */ 
        } 
 
    return (tick); 
    } 
 
/*************************************************************************** 
* sysTimestampLock - get the timestamp timer tick count 
* 
* This routine returns the current value of the timestamp timer tick counter. 
* The tick count can be converted to seconds by dividing by the return of 
* sysTimestampFreq(). 
* 
* This routine locks interrupts for cases where it is necessary to stop the 
* tick counter before reading it, or when two independent counters must 
* be read.  If interrupts are already locked, use sysTimestamp() instead. 
* 
* RETURNS: The current timestamp timer tick count. 
* SEE ALSO: sysTimestamp() 
*/ 
  
UINT32 sysTimestampLock (void) 
    { 
    UINT32 tick = 0; 
    register UINT32 * pTick; 
    register UINT32 * pPreload; 
    int lockKey; 
 
    if (sysTimestampRunning) 
        { 
        lockKey = intLock ();           /* LOCK INTERRUPTS */ 
 
        /* pTick = counter read register location */ 
        /* pPreload = counter preload register location */ 
 
        /* disable counting timer here */ 
 
        tick = *pTick;                  /* read counter value */ 
        *pPreload = tick - TS_SKEW;     /* set preload value */ 
                                          /* (with time-skew adjustment) */ 
 
        /* enable counting timer here */ 
 
        intUnlock (lockKey);            /* UNLOCK INTERRUPTS */ 
 
        tick -= (0xfff...);             /* adjust to incrementing value */ 
        } 
 
    return (tick); 
    } 
 
#endif  /* INCLUDE_TIMESTAMP */</a></b></pre>
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</dl>

<h4 class="EntityTitle"><a name="86024"><font face="Helvetica, sans-serif" size="-1" class="sans">Example G-3:&nbsp;&nbsp;Timestamp Drivers for the VxWorks System Clock Timer</font></a></h4>
<dl class="margin">

<dl class="margin">

<dd><p class="Body"><a name="86098"> </a>This example shows a skeleton timestamp driver for systems that have no suitable spare timers, so that timestamps must be derived from the VxWorks system clock timer. See <a href="x-timestamp4.html#85777"><i class="title">Using the VxWorks System Clock Timer</i></a>, for a discussion of the most important details involved in writing this kind of driver.</p>
</dl>

<dl class="margin">

<dd><pre class="Code"><b><a name="86284">/* sampleCTimer.c - sample C timer library */ 
 
/* Copyright 1994 Wind River Systems, Inc. */ 
#include "copyright_wrs.h" 
 
/* 
modification history 
-------------------- 
01a,23mar94,dzb  written. 
*/ 
 
/* 
DESCRIPTION 
This library contains sample routines to manipulate the timer functions on 
the sample C chip with a board-independent interface.  This library handles 
the timestamp timer facility. 
 
To include the timestamp timer facility, the macro INCLUDE_TIMESTAMP must be 
defined.</a></b><dd>
 
<b><a name="87767">NOTE:  This module provides an example of a VxWorks timestamp timer driver 
implemented by reading the system clock timer counter.  It illustrates the 
structures and routines discussed in the Appendix, "Creating a VxWorks 
Timestamp Driver."  This module is only a template. In its current form,  
it will not compile. 
*/ 
 
#ifdef  INCLUDE_TIMESTAMP 
 
#include "drv/timer/timestampDev.h" 
#include "drv/timer/sampleCTimer.h" 
 
/* Locals */  
 
LOCAL BOOL    sysTimestampRunning = FALSE;      /* running flag */ 
 
/*************************************************************************** 
* 
* sysTimestampConnect - connect a user routine to the timestamp timer 
*                        &nbsp;interrupt 
* 
* This routine specifies the user interrupt routine to be called at each 
* timestamp timer interrupt.  It does not enable the timestamp timer itself. 
* 
* RETURNS: OK, or ERROR if sysTimestampInt() interrupt handler is not used. 
*/ 
  
STATUS sysTimestampConnect 
    ( 
    FUNCPTR routine,    /* routine called at each timestamp timer interrupt */ 
    int arg             /* argument with which to call routine */ 
    ) 
    { 
    /* ERROR indicates that the system clock tick specifies a rollover event */ 
 
    return (ERROR); 
    } 
 
/*************************************************************************** 
* 
* sysTimestampEnable - initialize and enable the timestamp timer 
* 
* This routine connects the timestamp timer interrupt and initializes the 
* counter registers.  If the timestamp timer is already running, this routine 
* merely resets the timer counter. 
* 
* Set the rate of the timestamp timer input clock explicitly within the 
* BSP, in the sysHwInit() routine.  This routine does not initialize 
* the timer clock rate. 
* 
* RETURNS: OK, or ERROR if the timestamp timer cannot be enabled. 
*/</a></b><dd>
 
<b><a name="87768">STATUS sysTimestampEnable (void) 
    { 
    if (sysTimestampRunning) 
        return (OK); 
     
    sysTimestampRunning = TRUE; 
 
    sysClkEnable ();            /* ensure the system clock is running */ 
  
    return (OK); 
    } 
 
/*************************************************************************** 
* sysTimestampDisable - disable the timestamp timer 
* 
* This routine disables the timestamp timer.  Interrupts are not disabled. 
* However, the tick counter does not increment after the timestamp timer 
* is disabled, ensuring that interrupts are no longer generated. 
* 
* RETURNS: OK, or ERROR if the timestamp timer cannot be disabled. 
*/ 
  
STATUS sysTimestampDisable (void) 
    { 
    sysTimestampRunning = FALSE; 
 
    return (ERROR); 
    } 
 
/*************************************************************************** 
* 
* sysTimestampPeriod - get the timestamp timer period 
* 
* This routine returns the period of the timer in timestamp ticks. 
* The period, or terminal count, is the number of ticks to which the 
* timestamp timer counts before rolling over and restarting the counting 
* process. 
* 
* RETURNS: The period of the timer in timestamp ticks. 
*/ 
  
UINT32 sysTimestampPeriod (void) 
    { 
    /* return the system clock period in timestamp ticks */ 
 
    return (sysTimestampFreq ()/sysClkRateGet ())        
    } 
 
/*************************************************************************** 
* 
* sysTimestampFreq - get the timestamp timer clock frequency 
* 
* This routine returns the frequency of the timer clock, in ticks per second. 
* The rate of the timestamp timer should be set explicitly in the BSP, 
* in the sysHwInit() routine. 
* 
* RETURNS: The timestamp timer clock frequency, in ticks per second. 
*/ 
  
UINT32 sysTimestampFreq (void) 
    { 
    UINT32 timerFreq; 
 
    /* 
     * Return the timestamp tick output frequency here. 
     * This value can be determined from the following equation: 
     *     timerFreq = clock input frequency / prescaler 
     *  
     * When possible, read the clock input frequency and prescaler values 
     * directly from chip registers. 
     */ 
  
    return (timerFreq); 
    } 
 
/*************************************************************************** 
* 
* sysTimestamp - get the timestamp timer tick count 
* 
* This routine returns the current value of the timestamp timer tick counter. 
* The tick count can be converted to seconds by dividing by the return of 
* sysTimestampFreq(). 
* 
* Call this routine with interrupts locked.  If interrupts are 
* not already locked, use sysTimestampLock() instead. 
* 
* RETURNS: The current timestamp timer tick count. 
* SEE ALSO: sysTimestampLock() 
*/ 
  
UINT32 sysTimestamp (void) 
    { 
    /* return the system clock timer tick count here */ 
    } 
 
/*************************************************************************** 
* 
* sysTimestampLock - get the timestamp timer tick count 
* 
* This routine returns the current value of the timestamp timer tick counter. 
* The tick count can be converted to seconds by dividing by the return of 
* sysTimestampFreq(). 
* 
* This routine locks interrupts for cases where it is necessary to stop the 
* tick counter before reading it, or when two independent counters must 
* be read.  If interrupts are already locked, use sysTimestamp() instead. 
* 
* RETURNS: The current timestamp timer tick count. 
* 
* SEE ALSO: sysTimestamp() 
*/ 
  
UINT32 sysTimestampLock (void) 
    { 
    /* 
     * Return the system clock timer tick count here. 
     * Interrupts do *not* need to be locked in this routine if 
     * the counter does not need to be stopped to be read. 
     */ 
    } 
 
#endif  /* INCLUDE_TIMESTAMP */</a></b></pre>
</dl>

<dl class="margin">

<dd><p class="Body"><a name="86286"> </a></p>
<dd><p class="Body"><a name="85959"> </a></p>
</dl>

</dl>


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