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Deviation in AWU clock frequency

Question asked by WoRo on Aug 7, 2013

I'm using the BEEP function of my STM8S105, but it doesn't work as expectet.  It's not that I need the exact frequency, but I want to know, why it differs from the correct vallue, when chosing HSE as timebase.

Basic settings:
- external quartz crystal 16MHz
- MCU options:
   EXTCLK: External Oscillator (OPT4 EXTCLK = 0)
   PRSC: 16MHz to 128kHz (OPT4 PRSC[1:0] = 00)

1st test:
 option CKAWUSEL: High Speed External (OPT4 CKAWUSEL = 0)
-> expected fBEEP: 4kHz; real result: 2.69kHz :o(    ????

2nd test:
- option  CKAWUSEL: Low Speed Internal (OPT4 CKAWUSEL = 1)
-> expected fBEEP: 4kHz; real result: 4.09kHz :o)

Any clue???