Odd Time of Day Reported with Ticker

[Joel Sherrill]

On Jan 19, 2016 3:53 AM, "Sebastian Huber" <
sebastian.huber at embedded-brains.de> wrote:
>
> The problem is that you set the time via rtems_clock_set() in Init(). The
you wait via rtems_task_wake_after(5s in ticks). With a
rtems_task_wake_after(n) you wait to the n-th next tick, thus your wait
interval is slightly less than 5s in most cases.

That makes sense but it unfortunately makes the obvious explanation of
ticker a bit more complicated. :)

0: RTEMS starts
0+t1: clock_set to TIME
0+t[234]: three wake afters

500th clock tick is now exactly five seconds from time 0 but TIME+5 seconds
minus t1 clock time.

The thing that surprised me was that when I hacked in changes to use
rtems_clock_get_tod_timeval(), the times do not indicate that 5 seconds of
delay actually occurred.

TA1 599562000:1088
TA2 599562000:2143
TA3 599562000:3199
TA1 599562004:997954
TA2 599562009:977896
TA1 599562009:978937
TA3 599562014:957903
TA1 599562014:958944
TA2 599562019:957907
The tasks are delaying 500, 1000, and 1500 ticks with nanoseconds_per_tick
= 10000000. Delay operations are guaranteed to be a minimum of the
requested amount and this is not being honored.

I know this is a duration specified in clock ticks but it is really (ticks
* nanoseconds per tick) long in real time.

I have not checked delays like sleep() and nanosleep() but tick based ones
are 1 tick too short.

--joel


> On 18/01/16 00:19, Joel Sherrill wrote:
>>
>> Hi
>>
>> With the recent clock changes, I am noticing that on some BSPs
>> ticker is reporting times 4, 9, 14, ... instead of 5, 10, 15.
>>
>> It looks like the time is 4.9999999 when it should simply be 5 so
>> ticker just reports 4.
>>
>> Given this is a visible change in behavior, I would like to know
>> what causes it and how it can be resolved?
>>
>> Thanks.
>>
>> --joel
>>
>>
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>> devel at rtems.org
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>
>
> --
> Sebastian Huber, embedded brains GmbH
>
> Address : Dornierstr. 4, D-82178 Puchheim, Germany
> Phone   : +49 89 189 47 41-16
> Fax     : +49 89 189 47 41-09
> E-Mail  : sebastian.huber at embedded-brains.de
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>
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>
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