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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'>This solution is actually very robust. Only
if the number of microseconds per tick is very small (~10 us) should you get
problems. This is, if two clock interrupts can occur while interrupts are
disabled. But we consider this to be impossible.<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'>Remember that the clock ticks and nanoseconds
are read while interrupts are disabled. So after the disabling of interrupts at
most only one clock tick could occur.<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'>The _<i><span style='font-style:italic'>TOD</span></i>_Tickle_ticks
only states that one more clock tick occurred. The nanoseconds field is not
updated. Haven’t tested, but don’t believe that just by commenting those lines
the problem will be solved.<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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face="Times New Roman"><span style='font-size:12.0pt'>
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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
10:57 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'>The current solucion also gets a problem because really depends on the
CONFIGURE_MICROSECONDS_PER_TICK parameter. If this value is small enough it is
possible to get another overrun of tv_nsec while executing<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><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> /*
code added */</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>
/* if an interrupt occurred while interrupts were disabled and the nanoseconds
is too little */</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>
/* means that a clock interrupt occurred BEFORE the nanoseconds were read */</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>
if (pending && offset.tv_nsec <
rtems_configuration_get_microseconds_per_tick() / 2) {</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>
struct timespec clockTick = {0,
rtems_configuration_get_microseconds_per_tick()*1000};</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>
_Timespec_Add_to(&offset, &clockTick); /* so add one clock tick to the
offset */</span></font><o:p></o:p></p>
<p><font size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>
}</span></font><o:p></o:p></p>
<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'>I see
that _TOD_Uptime is updated every clock tick
in cpukit/score/src/coretodtickle.c (see bellow) with microseconds
precision. It is not enough with the next patch?<o:p></o:p></span></font></p>
<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'>===
modified file 'cpukit/score/src/coretodgetuptime.c'<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>---
cpukit/score/src/coretodgetuptime.c 2009-03-31 07:56:38 +0000<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>+++
cpukit/score/src/coretodgetuptime.c 2009-03-31 09:49:25 +0000<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>@@ -20,6
+20,7 @@<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> #include
<rtems/score/isr.h><o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> #include
<rtems/score/timespec.h><o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> #include
<rtems/score/tod.h><o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>+#include
<rtems/config.h><o:p></o:p></span></font></p>
<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'> /*<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'> *
_TOD_Get_uptime<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>@@ -46,8
+47,8 @@<o:p></o:p></span></font></p>
<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'>
_ISR_Disable( level );<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>
*uptime = _TOD_Uptime;<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>-
if ( _Watchdog_Nanoseconds_since_tick_handler )<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>-
offset.tv_nsec = (*_Watchdog_Nanoseconds_since_tick_handler)();<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>+//
if ( _Watchdog_Nanoseconds_since_tick_handler )<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>+//
offset.tv_nsec = (*_Watchdog_Nanoseconds_since_tick_handler)();<o:p></o:p></span></font></p>
<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'>
_ISR_Enable( level );<o:p></o:p></span></font></p>
<p><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'><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 11:22 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'>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 :(. </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'>In either case, here’s the function for the ERC32 board (I
know, the names can be improved):</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'>#define INTERRUPT_PENDING_ADDRESS 0x01F80048</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'>/**</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'> * RTC interrupt level</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'>#define RTC_ISR_INTERRUPT_LEVEL 13</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'>#define RTC_INTERRUPT_PENDING_MASK (1 <<
RTC_ISR_INTERRUPT_LEVEL)</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'>uint32_t isClockInterruptPending() {</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'> uint32_t *pointer_pending = (uint32_t *)
INTERRUPT_PENDING_ADDRESS;</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'> return pending (*pointer_pending ) &
RTC_INTERRUPT_PENDING_MASK;</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'> </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>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
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<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center>
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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
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; <a
href="mailto:rtems-users@rtems.com" target="_blank">rtems-users@rtems.com</a><o:p></o:p></span></font></p>
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<div>
<p class=MsoNormal><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma'><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: Bug with clock
nanoseconds<o:p></o:p></span></font></p>
</div>
</div>
</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'>Yep,<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'>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><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 Tue,
Mar 31, 2009 at 10:30 AM, Manuel Coutinho <<a
href="mailto:manuel.coutinho@edisoft.pt" target="_blank">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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<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>
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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>
<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>
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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>
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<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>
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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>
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<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Best
regards,<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>
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<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Aitor<o:p></o:p></span></font></p>
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<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>
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<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>
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<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>
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<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>
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<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>
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<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>>
.....<br>
<br>
<br>
....<o:p></o:p></span></font></p>
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<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>
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<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>
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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>
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