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base:tod_calibration

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base:tod_calibration [2019-05-19 07:49] – created socibase:tod_calibration [2019-05-19 08:04] (current) soci
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-The code below sets the TOD 50/60 Hz pre-scaler of CIA. It needs to correspond to the power line frequency which might or might not relate to the video standard.+The code below initializes the TOD 50/60 Hz pre-scaler of CIA based on the detected AC line frequency.
  
 The idea is to use the horizontal retrace frequency (15.6-16 KHz) as base to measure the TOD tick interval. If it takes longer then a threshold the 50 Hz pre-scaler is used otherwise the 60 Hz one. The idea is to use the horizontal retrace frequency (15.6-16 KHz) as base to measure the TOD tick interval. If it takes longer then a threshold the 50 Hz pre-scaler is used otherwise the 60 Hz one.
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   * Does not mess with timers or anything else   * Does not mess with timers or anything else
  
-Of course timer NMIs should be avoided during the measurement. If interrupts are already disabled it can be shortened by 3 bytes.+Of course timer NMIs should be avoided during calibration. If interrupts are already disabled it can be shortened by 3 bytes.
  
 <code> <code>
base/tod_calibration.txt · Last modified: 2019-05-19 08:04 by soci