prod/doc/analysis.hmac |
289 | 289 | <!-- ---------------------------------------------------------------------- --> |
290 | 290 | |
291 | 291 | |
292 | | <SUBSECTION title="Precision measurements"> |
| 292 | <SUBSECTION title="Precision measurements (atben)"> |
293 | 293 | |
294 | 294 | The clock frequency of <B>atben</B> can be measured with an accuracy |
295 | 295 | of about +/− 100 ppm using the program atrf-xtal. atrf-xtal |
... | ... | |
297 | 297 | The transmission time depends on the bit clock which is in turn derived |
298 | 298 | from the oscillator. |
299 | 299 | <PRE> |
300 | | atrf-xtal 100 |
| 300 | ben# atrf-xtal 100 |
301 | 301 | </PRE> |
302 | 302 | The number reported is the number of poll loops the CPU counted. This |
303 | 303 | value should be compared to a reference count obtained with a known to |
... | ... | |
305 | 305 | <P> |
306 | 306 | <TABLE frame="border" cellpadding="2"> |
307 | 307 | <TR><TH align="left">Difference<TH align="left">Action |
308 | | <TR><TD>> +/− 50 ppm<TD>Correct operation |
| 308 | <TR><TD>< +/− 50 ppm<TD>Correct operation |
309 | 309 | <TR><TD>< −80 ppm<TD>Check soldering of capacitors; |
310 | 310 | check for contamination around crystal |
311 | 311 | <TR><TD>> +120 ppm<TD>idem |
312 | 312 | <TR><TD>Other<TD>Deviation can be compensated by adjusting trim value |
313 | 313 | </TABLE> |
314 | 314 | |
| 315 | |
| 316 | <!-- ---------------------------------------------------------------------- --> |
| 317 | |
| 318 | |
| 319 | <SUBSECTION title="Precision measurements (atusb)"> |
| 320 | |
| 321 | The clock frequency of <B>atusb</B> can be measured with an accuracy |
| 322 | of about +/− 1 ppm relative to the PC's NTP-disciplined clock. |
| 323 | <PRE> |
| 324 | pc# atrf-xtal 10000 |
| 325 | </PRE> |
| 326 | This measurement runs for 10−60 seconds, depending on system load. |
| 327 | Note that, in order to reach such a high precision, it is imperative |
| 328 | that 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>< +/− 30 ppm<TD>Correct operation |
| 333 | <TR><TD>Other<TD>See the <B>atben</B> section above |
| 334 | </TABLE> |
| 335 | |
| 336 | |
315 | 337 | <END author="Werner Almesberger" date="<GEN_DATE>"> |
316 | 338 | </BODY> |
317 | 339 | </HTML> |