Date:2011-05-31 01:21:22 (12 years 9 months ago)
Author:Werner Almesberger
Commit:8c25bc2b63b28c891fd640b3b7b41e6008371eaf
Message:prod/doc/analysis.hmac: added atrf-xtal measurement on atusb; clarifictions

Files: prod/doc/analysis.hmac (3 diffs)

Change Details

prod/doc/analysis.hmac
289289<!-- ---------------------------------------------------------------------- -->
290290
291291
292<SUBSECTION title="Precision measurements">
292<SUBSECTION title="Precision measurements (atben)">
293293
294294The clock frequency of <B>atben</B> can be measured with an accuracy
295295of about +/&minus; 100 ppm using the program atrf-xtal. atrf-xtal
...... 
297297The transmission time depends on the bit clock which is in turn derived
298298from the oscillator.
299299<PRE>
300atrf-xtal 100
300ben# atrf-xtal 100
301301</PRE>
302302The number reported is the number of poll loops the CPU counted. This
303303value should be compared to a reference count obtained with a known to
...... 
305305<P>
306306<TABLE frame="border" cellpadding="2">
307307<TR><TH align="left">Difference<TH align="left">Action
308<TR><TD>&gt; +/&minus; 50 ppm<TD>Correct operation
308<TR><TD>&lt; +/&minus; 50 ppm<TD>Correct operation
309309<TR><TD>&lt; &minus;80 ppm<TD>Check soldering of capacitors;
310310  check for contamination around crystal
311311<TR><TD>&gt; +120 ppm<TD>idem
312312<TR><TD>Other<TD>Deviation can be compensated by adjusting trim value
313313</TABLE>
314314
315
316<!-- ---------------------------------------------------------------------- -->
317
318
319<SUBSECTION title="Precision measurements (atusb)">
320
321The clock frequency of <B>atusb</B> can be measured with an accuracy
322of about +/&minus; 1 ppm relative to the PC's NTP-disciplined clock.
323<PRE>
324pc# atrf-xtal 10000
325</PRE>
326This measurement runs for 10&minus;60 seconds, depending on system load.
327Note that, in order to reach such a high precision, it is imperative
328that the PC clock be disciplined by NTP.
329<P>
330<TABLE frame="border" cellpadding="2">
331<TR><TH align="left">Difference<TH align="left">Action
332<TR><TD>&lt; +/&minus; 30 ppm<TD>Correct operation
333<TR><TD>Other<TD>See the <B>atben</B> section above
334</TABLE>
335
336
315337<END author="Werner Almesberger" date="<GEN_DATE>">
316338</BODY>
317339</HTML>

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