Date:2011-05-18 22:49:58 (12 years 10 months ago)
Author:Werner Almesberger
Commit:d2fda376d4a1b7522cccb3e9e3062ab2e70550d4
Message:prod/doc/analysis.html: added precision clock measurement for atben

Files: prod/doc/analysis.html (1 diff)

Change Details

prod/doc/analysis.html
8989
9090<H3>Precision measurements</H3>
9191
92The clock frequency of <B>atben</B> can be measured with an accuracy
93of about +/- 100 ppm using the program <B>atrf-xtal</B>. <B>atrf-xtal</B>
94runs directly on the Ben and measures the duration of packet transmissions.
95The transmission time depends on the bit clock which is in turn derived
96from the oscillator.
97<P>
98<B>atrf-xtal</B> requires exclusive access to the <B>atben</B>. If a
99proxy is running, it has to be removed first.
100<PRE>
101killall atrf-proxy
102atrf-xtal 100
103</PRE>
104The number reported is the number of poll loops the CPU counted. This
105value should be compared to a reference count obtained with a known to
106be good <B>atben</B> board and the same Ben at a comparable temperature.
107<P>
108<TABLE>
109<TR><TH align="left">Difference<TH align="left">Action
110<TR><TD>&gt; +/- 50 ppm<TD>Correct operation
111<TR><TD>&lt; -80 ppm<TD>Check soldering of capacitors;
112  check for contamination around crystal
113<TR><TD>&gt; +120 ppm<TD>idem
114<TR><TD>Other<TD>Divergence can be compensated by adjusting trim value
115</TABLE>
116
92117<P>
93118<HR>
94119Up: <A href="index.html">Production and testing</A>&nbsp;

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