more robust MB check

src/libsrc/apple/sndseq.pla

@@ -213,7 +213,7 @@ asm psgWrite(pVIA, reg, val)#0
         INX
         RTS
 end
-asm viaCheck(pVIA)#2
+asm viaCheck(pVIA)#1
         PHP
         SEI
         LDA     ESTKL,X
@@ -223,23 +223,18 @@ asm viaCheck(pVIA)#2
         STX     ESP
         LDX     #$80
         LDY     #$04
+        SEC
 -       LDA     (TMP),Y
         BMI     +
         DEX
         BNE     -
         TXA                 ; TIMEOUT
         BEQ     ++
-+       TAX
-        LDA     (TMP),Y
-++      TAY
-        TXA
-        LDX     ESP
-        DEX
++       SBC     (TMP),Y
+++      LDX     ESP
         STA     ESTKL,X
-        STY     ESTKL+1,X
         LDA     #$00
         STA     ESTKH,X
-        STA     ESTKH+1,X
         PLP
         RTS
 end
@@ -404,13 +399,8 @@ end
 // Search slots for MockingBoard
 //
 def mbTicklePSG(pVIA)
-    byte tmrBegin, tmrEnd
-    word tmrDiff
-    
-    tmrBegin, tmrEnd = viaCheck(pVIA)
-    tmrDiff = tmrEnd - tmrBegin
-    //puts("VIA address: $"); puth(pVIA); puts(" Timer Diff = "); puti(tmrDiff); putln
-    if tmrDiff == 10
+    //puts("VIA address: $"); puth(pVIA); puts(" Timer Diff = "); puti(viaCheck(pVIA)); putln
+    if viaCheck(pVIA) == 8 and viaCheck(pVIA) == 8 // Check twice
         pVIA->IER  = $7F  // Mask all interrupts
         //pVIA->ACR  = $00  // Stop T1 countdown
         pVIA->DDRB = $FF  // Output enable port A and B