Change Details
prod/doc/analysis.html |
89 | 89 | |
90 | 90 | <H3>Precision measurements</H3> |
91 | 91 | |
| 92 | The clock frequency of <B>atben</B> can be measured with an accuracy |
| 93 | of about +/- 100 ppm using the program <B>atrf-xtal</B>. <B>atrf-xtal</B> |
| 94 | runs directly on the Ben and measures the duration of packet transmissions. |
| 95 | The transmission time depends on the bit clock which is in turn derived |
| 96 | from the oscillator. |
| 97 | <P> |
| 98 | <B>atrf-xtal</B> requires exclusive access to the <B>atben</B>. If a |
| 99 | proxy is running, it has to be removed first. |
| 100 | <PRE> |
| 101 | killall atrf-proxy |
| 102 | atrf-xtal 100 |
| 103 | </PRE> |
| 104 | The number reported is the number of poll loops the CPU counted. This |
| 105 | value should be compared to a reference count obtained with a known to |
| 106 | be 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>> +/- 50 ppm<TD>Correct operation |
| 111 | <TR><TD>< -80 ppm<TD>Check soldering of capacitors; |
| 112 | check for contamination around crystal |
| 113 | <TR><TD>> +120 ppm<TD>idem |
| 114 | <TR><TD>Other<TD>Divergence can be compensated by adjusting trim value |
| 115 | </TABLE> |
| 116 | |
92 | 117 | <P> |
93 | 118 | <HR> |
94 | 119 | Up: <A href="index.html">Production and testing</A> |
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