[VM][FMTOWNS][YM2612] Fix clock of OPN2 to 1999.46KHz.

  Thanks to YS-11 (Yamakawa) San, the author of TSUGARU emulator.

diff --git a/source/src/vm/fmtowns/fmtowns.cpp b/source/src/vm/fmtowns/fmtowns.cpp
index 0eab430..cb2dc57 100644 (file)
--- a/source/src/vm/fmtowns/fmtowns.cpp
+++ b/source/src/vm/fmtowns/fmtowns.cpp
@@ -838,12 +838,25 @@ void VM::initialize_sound(int rate, int samples)
        beep->initialize_sound(rate, 8000);
 
        // init OPN2
+       #if 0
        // MASTER CLOCK MAYBE 600KHz * 12 = 7200KHz .
        // From FM-Towns Technical Databook (Rev.2), Page 201
-       opn2->initialize_sound(rate, (int)(600.0e3 * 12.0) , samples, 0.0, 0.0);
-       //opn2->initialize_sound(rate, (int)(8000.0e3) , samples, 0.0, 0.0);
-       //opn2->initialize_sound(rate, (int)(600.0e3 * 6.0) , samples, 0.0, 0.0);
-
+       // opn2->initialize_sound(rate, (int)(600.0e3 * 12.0) , samples, 0.0, 0.0);
+       #else
+       // But...20230330 K.O:
+       // From src/ym2612/ym2612.h of Tsugaru below quote.
+       // Thanks to YS-11 San.
+       //
+       // What exactly is the master clock given to YM2612 of TOWNS?
+       // FM Towns Technical Databook tells internal clock is 600KHz on page 201.
+       // However, after calibrating the tone to match real Towns, it must be 690KHz.  Is it correct?
+       // Master clock must be the internal clock times pre scaler.  But, we don't know the default pre scalar value.
+       // Let's say it is 3.  Then, 690KHz times 3=2070KHz.  Sounds reasonable.
+       // But, now FM77AV's YM2203C uses master clock frequency of 1228.8KHz.
+       // And after calibration we know the ratio between the two.
+       // From there, 1228.8*1698/1038=1999.46.  2MHz.  Makes more sense.
+       opn2->initialize_sound(rate, (int)(((1228.8e3 * 1698.0) / 1038.0) * 4.0) , samples, 0.0, 0.0);
+       #endif
        // init PCM
        rf5c68->initialize_sound(rate, samples);