Added PSG initialization

The Mockingboard Developer’s Toolkit included as interrupt based MCS
player that was obviously based on the original sources but included
important corrections. This included the PSG initialization and a
correction the frequency tables.
The code was moved to the address $8500 to match that implementation.

src/MUSIC SOURCE.s

@@ -1,7 +1,7 @@
                          ;"WILL HARVEY'S MUSIC"
                          ;"COPYRIGHT (C) 1983"
-          ORG $4900
-          OBJ $4900
+          ORG $8500
+          OBJ $8500
 ORB       EQU $C400
 ORA       EQU $C401
 ORB2      EQU $C480
@@ -18,6 +18,7 @@ IER       EQU $C40E
 
 SONGADD   EQU $6
 CHANNADD  EQU $D6
+
           JMP INTRUPT
           JMP INIT
           JMP INITMOCK
@@ -52,7 +53,7 @@ FREQLOS   HEX 1E1F20222426292C
           HEX B7C2CEDAE7F40312
           HEX 2334465A6E849BB3
           HEX CDE9062545688CB3
-          HEX DC0836679BD20000
+          HEX DC0836679BD20101
 FREQHIS   HEX 0000000000000000
           HEX 0000000000000000
           HEX 0000000000000000
@@ -269,12 +270,15 @@ SONGADDS  LDA STARTADD
           STA TEMP2
           JSR STOPVOIC
           RTS
-INIT      JSR SONGADDS
+INIT      JSR INITPAR
+          JSR SONGADDS
           LDA #$F8
           STA $307
           STA $317
           LDA #%01000000
           STA ACR
+          LDA #%01111111
+          STA IER
           LDA #%11000000
           STA IFR
           STA IER
@@ -321,3 +325,15 @@ PAUSE     SEI
 
 CONTINUE  CLI
           RTS
+
+INITPAR   LDX #0
+]LOOP     LDA PARAMS,X
+          STA $0300,X
+          INX
+          CPX #$20
+          BNE ]LOOP
+          RTS
+PARAMS    HEX 010001000100003F
+          HEX 0000000000000000
+          HEX 010001000100003F
+          HEX 0000000000000000