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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>All<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>I wonder if I could tap in to the groups experience
with writing ISRs within a typical RTEMS driver model.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>We have written a number of drivers for various low
level UART styled devices. These devices can work in either polled or interrupt
mode. In interrupt mode we use the SIMPLE BINARY SEMAPHORE to synchronise
events between our ISRs and the Read and Write routines of driver e.g. within
the ISR we use rtems_semaphore_release and within the read and write routines
block until rtems_semaphore_obtain is successful. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>What we have observed so far is that the ISR takes a
relatively long time to be serviced, 10us [200 clock cycles] up to 40us [800 clock
cycles], and that the time between releasing the semaphore within the ISR and
the Read or Write Routines being released varies considerably, 20us [400 clock
cycles] up to 80us [1600 clock cycles]. We also have noted that the time
between releasing the semaphore within the ISR and the Read or Write Routines being
released on the first time of execution always appears to be significantly
longer than subsequent times. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Our devices are attached directly to the interrupt
lines on a SPARC Leon 2 processor. The processor runs at 20 MHz and we are
using rtems 4.8.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>My first question would be are these delays typical
of an RTEMS based system?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Secondly is there a way of improving the performance
by reducing these latencies in some way? <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Lastly is the SIMPLE BINARY SEMAPHORE the correct
synchronisation mechanism to use in this instance?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>Thank you for in advance for your assistance.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'>
Jamie<o:p></o:p></span></font></p>
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