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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I’m not sure that the
isClockInterruptPending() is a function that can be available to all BSPs. Some
CPU might not support this. I don’t know :(. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>In either case, here’s the function for
the ERC32 board (I know, the names can be improved):<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>#define INTERRUPT_PENDING_ADDRESS
0x01F80048<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>/**<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> * RTC interrupt level<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> **/<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>#define RTC_ISR_INTERRUPT_LEVEL 13<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>#define RTC_INTERRUPT_PENDING_MASK (1
<< RTC_ISR_INTERRUPT_LEVEL)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>uint32_t isClockInterruptPending() {<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> uint32_t *pointer_pending = (uint32_t
*) INTERRUPT_PENDING_ADDRESS;<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> return pending (*pointer_pending ) &
RTC_INTERRUPT_PENDING_MASK;<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>}<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
aitorvs@googlemail.com [mailto:aitorvs@googlemail.com] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Aitor Viana<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, March 31, 2009 10:09
AM<br>
<b><span style='font-weight:bold'>To:</span></b> Manuel Coutinho<br>
<b><span style='font-weight:bold'>Cc:</span></b> Joel Sherrill;
rtems-users@rtems.com<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: Bug with clock
nanoseconds</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Yep,<o:p></o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>crystal clear. BTW, isClockInterruptPending() is not present in the
RTEMS distribution, it should be implemented for all BSPs I guess.<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Best regards,<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Aitor<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>On Tue, Mar 31, 2009 at 10:30 AM, Manuel Coutinho <<a
href="mailto:manuel.coutinho@edisoft.pt">manuel.coutinho@edisoft.pt</a>>
wrote:<o:p></o:p></span></font></p>
<div link=blue vlink=blue>
<div>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Hi. Thanks for testing in leon2…was just about to do that :)!</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Basically, the test aims to see that the clock is always
increasing. But the result is that, sometimes, it decreases.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>This happens when a clock tick occurs.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>The RTEMS algorithm to read the time consists of:</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>1. Disabling interrupts</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>2. Read how many clock interrupts occurred</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>3. Read nanoseconds elapsed</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>4. Enable interrupts</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>The problem occurs if an interrupt occurs between the 1 and 3
steps: -> the number of clock ticks is NOT updated (because interrupts are
disabled) and the nanoseconds field (which is read directly from the CPU
registers) is restarted.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>For example, the clock is 2 clock ticks and 99999 us (a clock
tick is just about to occur). Suppose you disable interrupts, read 2 clock
ticks, then the CPU clock counter overflows and the nanoseconds is reset to 0
and you read 0 nanoseconds. </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>You end up reading 2 clock ticks and 0 nanoseconds when in
fact you should read 3 clock ticks and 0 nanoseconds - you cannot stop the
clock counter (nor do you wish to!).</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Hope this explains the problem a little bit better :)</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>By the way, by glancing at the code of the remaining BSPs,
specifically at the Clock_driver_nanoseconds_since_last_tick macro, I don’t
believe this is a problem just with SPARC. I don’t see this problem address in
any board. But, of course, I might be wrong since it was just a very brief
look.</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Kind regards</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'>Manuel Coutinho</span></font><o:p></o:p></p>
<p><font size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:
Arial;color:navy'> </span></font><o:p></o:p></p>
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<div>
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<p><b><font size=2 face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
font-weight:bold'>From:</span></font></b><font size=2 face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma'> <a
href="mailto:aitorvs@googlemail.com" target="_blank">aitorvs@googlemail.com</a>
[mailto:<a href="mailto:aitorvs@googlemail.com" target="_blank">aitorvs@googlemail.com</a>]
<b><span style='font-weight:bold'>On Behalf Of </span></b>Aitor Viana<br>
<b><span style='font-weight:bold'>Sent:</span></b> Tuesday, March 31, 2009 8:31
AM<br>
<b><span style='font-weight:bold'>To:</span></b> Joel Sherrill<br>
<b><span style='font-weight:bold'>Cc:</span></b> Manuel Coutinho; <a
href="mailto:rtems-users@rtems.com" target="_blank">rtems-users@rtems.com</a><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: Bug with clock
nanoseconds</span></font><o:p></o:p></p>
</div>
<div>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Just
tried in tsim-leon and happens the same.<o:p></o:p></span></font></p>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>I didn't
completely understand what's the problem Manuel could you explain to me again?
is early in the morning :D<o:p></o:p></span></font></p>
</div>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Best
regards,<o:p></o:p></span></font></p>
</div>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Aitor<o:p></o:p></span></font></p>
</div>
<div>
<p style='margin-bottom:12.0pt'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'> <o:p></o:p></span></font></p>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>On Mon,
Mar 30, 2009 at 6:49 PM, Joel Sherrill <<a
href="mailto:joel.sherrill@oarcorp.com" target="_blank">joel.sherrill@oarcorp.com</a>>
wrote:<o:p></o:p></span></font></p>
<div>
<p style='margin-bottom:12.0pt'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>Manuel Coutinho wrote:<br>
><br>
> Hi<br>
><br>
><br>
><br>
> We have discovered a bug of RTEMS relating to the clock. Even though<br>
> we only tested it for the ERC32 board (for now), we believe it is<br>
> common throughout all the targets.<br>
><o:p></o:p></span></font></p>
</div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>No you
have discovered a bug in the ERC32's get nanoseconds since last<br>
tick handler.<br>
Apparently it doesn't recognize that is has been longer than a tick<br>
since the last clock<br>
tick. It should determine that is has overflowed and return 1 clock<br>
tick + partial clock<br>
tick.<br>
<br>
It is returning the wrong answer.<o:p></o:p></span></font></p>
<div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'><br>
><br>
><br>
> The test consists in checking if the time given by rtems_clock_get is<br>
> always increasing. The code is as follows:<br>
><br>
><br>
><o:p></o:p></span></font></p>
</div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>>
.....<br>
<br>
<br>
....<o:p></o:p></span></font></p>
<div>
<div>
<p style='margin-bottom:12.0pt'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>><br>
> As you can see, the problem is raised when a clock tick occurs: the<br>
> time read in “new” is older than “old”. This cannot happen since “new”<br>
> is updated AFTER “old”! This problem occurs if a clock interrupt is<br>
> triggered after the number of clock ticks have been read but BEFORE<br>
> the nanosecond field has been read. The resulting number of clock<br>
> ticks is “small” (should be plus one).<br>
><br>
><br>
><br>
> We can use the interrupt pending CPU registers info to determine if,<br>
> while we are reading the number of clock ticks that occurred and the<br>
> nanoseconds, a clock interrupt could be pending.<br>
><br>
><br>
><br>
> We do not have enough knowledge to say that this solution can be used<br>
> for all boards (determining if an interrupt is pending). In the SPARC<br>
> architecture, at least, it is possible. If it is possible in all<br>
> architectures, then a solution to RTEMS would be to change the code of<br>
> the _TOD_Get_uptime function to:<br>
><br>
><br>
><br>
><br>
><br>
> void _TOD_Get_uptime(struct timespec *uptime) {<br>
><br>
> ISR_Level level;<br>
><br>
> struct timespec offset;<br>
><br>
> volatile uint32_t pending;<br>
><br>
><br>
><br>
> /* assume uptime checked by caller */<br>
><br>
><br>
><br>
> offset.tv_sec = 0;<br>
><br>
> offset.tv_nsec = 0;<br>
><br>
><br>
><br>
> _ISR_Disable(level);<br>
><br>
> *uptime = _TOD_Uptime;<br>
><br>
> if (_Watchdog_Nanoseconds_since_tick_handler)<br>
><br>
> offset.tv_nsec =
(*_Watchdog_Nanoseconds_since_tick_handler)();<br>
><br>
><br>
><br>
> /* code added: */<br>
><br>
> pending = isClockInterruptPending();<br>
><br>
><br>
><br>
> _ISR_Enable(level);<br>
><br>
><br>
><br>
> /* code added */<br>
><br>
> /* if an interrupt occurred while interrupts were disabled
and the<br>
> nanoseconds is too little */<br>
><br>
> /* means that a clock interrupt occurred BEFORE the
nanoseconds<br>
> were read */<br>
><br>
> if (pending && offset.tv_nsec <<br>
> rtems_configuration_get_microseconds_per_tick() / 2) {<br>
><br>
> struct timespec clockTick = {0,<br>
> rtems_configuration_get_microseconds_per_tick()*1000};<br>
><br>
> _Timespec_Add_to(&offset, &clockTick);
/* so add one clock<br>
> tick to the offset */<br>
><br>
> }<br>
><br>
><br>
><br>
> /* else, the clock tick occurred AFTER the nanoseconds were
read,<br>
> so no problem */<br>
><br>
><br>
><br>
> _Timespec_Add_to(uptime, &offset);<br>
><br>
> }<br>
><br>
><br>
><br>
><br>
><br>
> At least, with these modifications, the test passes :)!<br>
><br>
><br>
><br>
> Kind regards<br>
><br>
> Manuel Coutinho<br>
><o:p></o:p></span></font></p>
</div>
</div>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>--<br>
Joel Sherrill, Ph.D. Director of
Research & Development<br>
joel.sherrill@OARcorp.com On-Line Applications Research<br>
Ask me about RTEMS: a free RTOS Huntsville AL 35805<br>
Support Available (256)
722-9985<br>
<br>
<br>
_______________________________________________<br>
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<a href="http://rtems.rtems.org/mailman/listinfo/rtems-users" target="_blank">http://rtems.rtems.org/mailman/listinfo/rtems-users</a><o:p></o:p></span></font></p>
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<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> <o:p></o:p></span></font></p>
</div>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
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