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cnet's Timers

A total of 10 software timer queues are supported to provide a call-back mechanism for user code. For example, when a data frame is transmitted a timer is typically created which will expire sometime after that frame's acknowledgement is expected. Timers are referenced via unique values termed timers of datatype CnetTimer.

When a timer expires, the event handler for the corresponding event (one of EV_TIMER1..EV_TIMER10) is invoked with the event and unique timer as parameters.

Timers may be cancelled with CNET_stop_timer to prevent them expiring (for example, if the acknowledgement frame arrives before the timer expires). Timers are automatically cancelled as a result of their handler being invoked.

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There are an unlimited number of timers

It is important to understand that an unlimited number of timers may be started on each queue - there are not just 10 timers. For example, the following section of code: 


void timeouts(CnetEvent ev, CnetTimer timer, CnetData data)
{
    int i = (int)data;

    (void)printf("tick number %d\n", i);
}

void reboot_node(CnetEvent ev, CnetTimer timer, CnetData data)
{
    (void)CNET_set_handler(EV_TIMER3, timeouts, 0);
    for(i=1 ; i<=10 ; ++i)
      (void)CNET_start_timer(EV_TIMER3, i*1000L, (CnetData)i);
}

will produce output identical to that from: 


void timeouts(CnetEvent ev, CnetTimer timer, CnetData data)
{
    int i = (int)data;

    printf("tick number %d\n", i);
    if(i < 10)
	(void)CNET_start_timer(EV_TIMER3, 1000L, (CnetData)i+1);
}

void reboot_node(CnetEvent ev, CnetTimer timer, CnetData data)
{
    (void)CNET_set_handler(EV_TIMER3, timeouts, 0);
    (void)CNET_start_timer(EV_TIMER3, 1000L, (CnetData)1);
}

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Timer functions

CnetTimer CNET_start_timer(CnetEvent ev, long msec, CnetData data)

Requests that a new timer be created which will expire in the indicated number of milliseconds. One of the 10 timer queues may be requested by passing one of the event types EV_TIMER1..EV_TIMER10. A unique timer is returned to distinguish this newly created timer from all others. This timer should later be used in subsequent calls to CNET_stop_timer(). If a new timer cannot be created, NULLTIMER will be returned.

Possible errors: ER_BADARG.

int CNET_stop_timer(CnetTimer timer)

Requests that the indicated timer be cancelled (before it has expired).

Possible errors: ER_BADTIMER.

int CNET_timer_data(CnetTimer timer, CnetData *data)

Allows the CnetData value for the indicated CnetTimer value to be recovered. The timer is not cancelled.

Possible errors: ER_BADTIMER, ER_BADARG.

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cnet was written and is maintained by Chris McDonald (chris@cs.uwa.edu.au)