z80: protect or avoid BC wherever it's used

For the IY->BC move, of course.

blk/310

@@ -1,4 +1,4 @@
-CODE PICK
+CODE PICK EXX, ( protect BC )
     HL POP,
     ( x2 )
     L SLA, H RL,
@@ -10,6 +10,6 @@ CODE PICK
     EXDEHL,
     HL PS_ADDR LDdn,
     DE SUBHLd,
-    CC lblofl @ JPc, ( abortUnderflow-B298 )
+    IFC, EXX, lblofl @ JP, THEN,
     BC PUSH,
-;CODE
+EXX, ( unprotect BC ) ;CODE

blk/319

@@ -1,16 +1,16 @@
-CODE *  ( DE * BC -> DE (high) and HL (low) )
+CODE * EXX, ( protect BC )
+    ( DE * BC -> DE (high) and HL (low) )
     DE POP, BC POP, chkPS,
     HL 0 LDdn,
     A 0x10 LDri,
-( loop )
-    HL ADDHLd,
-    E RL, D RL,
-    JRNC, 4 A, ( noinc )
-    BC ADDHLd,
-    JRNC, 1 A, ( noinc )
-    DE INCd,
-( noinc )
-    A DECr,
-    JRNZ, -14 A, ( loop )
+    BEGIN,
+        HL ADDHLd,
+        E RL, D RL,
+        IFC,
+            BC ADDHLd,
+            IFC, DE INCd, THEN,
+        THEN,
+        A DECr,
+    JRNZ, AGAIN,
     HL PUSH,
-;CODE
+EXX, ( unprotect BC ) ;CODE

blk/320

@@ -1,16 +1,15 @@
 ( Borrowed from http://wikiti.brandonw.net/ )
 ( Divides AC by DE and places the quotient in AC and the
   remainder in HL )
-CODE /MOD
-    DE POP,
-    BC POP,
-    chkPS,
-    A B LDrr,
-    B 16 LDri,
+CODE /MOD EXX, ( protect BC )
+    DE POP, BC POP, chkPS,
+    A B LDrr, B 16 LDri,
     HL 0 LDdn,
-
-
-
-
-
-                                                      ( cont. )
+    BEGIN,
+        SCF, C RL, RLA,
+        HL ADCHLd, DE SBCHLd,
+        IFC, DE ADDHLd, C DECr, THEN,
+    DJNZ, AGAIN,
+    B A LDrr,
+    HL PUSH, BC PUSH,
+EXX, ( unprotect BC ) ;CODE

blk/321

@@ -1,15 +0,0 @@
-    BEGIN, ( loop )
-        SCF,
-        C RL,
-        RLA,
-        HL ADCHLd,
-        DE SBCHLd,
-        IFC,
-            DE ADDHLd,
-            C DECr,
-        THEN,
-    DJNZ, AGAIN, ( loop )
-    B A LDrr,
-    HL PUSH,
-    BC PUSH,
-;CODE

blk/324

@@ -1,13 +1,13 @@
-CODE PC!
+CODE PC! EXX, ( protect BC )
     BC POP,
     HL POP,
     L OUT(C)r,
-;CODE
+EXX, ( unprotect BC ) ;CODE
 
-CODE PC@
+CODE PC@ EXX, ( protect BC )
     BC POP,
     chkPS,
     H 0 LDri,
     L INr(C),
     HL PUSH,
-;CODE
+EXX, ( unprotect BC ) ;CODE

blk/329

@@ -3,13 +3,13 @@ CODE CMP
     DE  POP,
     chkPS,
     DE SUBHLd,
-    BC 0 LDdn,
+    DE 0 LDdn,
     IFNZ, ( < or > )
-        BC INCd,
+        DE INCd,
         IFNC, ( < )
-            BC DECd,
-            BC DECd,
+            DE DECd,
+            DE DECd,
         THEN,
     THEN,
-    BC PUSH,
+    DE PUSH,
 ;CODE

blk/334

@@ -1,12 +1,13 @@
 CODE RSHIFT ( n u -- n )
-    BC POP, ( u )
+    DE POP, ( u )
     HL POP, ( n )
     chkPS,
-    B C LDrr,
-    B INCr, B DECr, IFNZ,
+    A E LDrr,
+    A ORr, IFNZ,
         BEGIN,
             H SRL, L RR,
-        DJNZ, AGAIN,
+            A DECr,
+        JRNZ, AGAIN,
     THEN,
     HL PUSH,
 ;CODE

blk/335

@@ -1,12 +1,13 @@
 CODE LSHIFT ( n u -- n )
-    BC POP, ( u )
+    DE POP, ( u )
     HL POP, ( n )
     chkPS,
-    B C LDrr,
-    B INCr, B DECr, IFNZ,
+    A E LDrr,
+    A ORr, IFNZ,
         BEGIN,
             L SLA, H RL,
-        DJNZ, AGAIN,
+            A DECr,
+        JRNZ, AGAIN,
     THEN,
     HL PUSH,
 ;CODE

blk/493

@@ -3,14 +3,14 @@ CODE (key)
     0x28 RST,
     PUSHA,
 ;CODE
-CODE (emit)
+CODE (emit) EXX, ( protect BC )
     BC POP, ( c == @DSP arg ) chkPS,
     A 0x02 LDri, ( @DSP )
     0x28 RST,
-;CODE
-CODE AT-XY
+EXX, ( unprotect BC ) ;CODE
+CODE AT-XY EXX, ( protect BC )
     DE POP, H E LDrr, ( Y )
     DE POP, L E LDrr, ( X ) chkPS,
     A 0x0f LDri, ( @VDCTL ) B 3 LDri, ( setcur )
     0x28 RST,
-;CODE
+EXX, ( unprotect BC ) ;CODE

blk/494

@@ -3,10 +3,10 @@ CODE BYE
     HL 0 LDdn,
     A 0x16 LDri, ( @EXIT )
     0x28 RST,
-CODE @DCSTAT ( drv -- f )
+CODE @DCSTAT ( drv -- f ) EXX, ( protect BC )
     BC POP,
     chkPS,
     A 0x28 LDri, ( @DCSTAT )
     0x28 RST,
     PUSHZ,
-;CODE
+EXX, ( unprotect BC ) ;CODE

blk/495

@@ -1,4 +1,4 @@
-CODE @RDSEC ( drv cylsec addr -- f )
+CODE @RDSEC ( drv cylsec addr -- f ) EXX, ( protect BC )
     HL POP,
     DE POP,
     BC POP,
@@ -6,4 +6,4 @@ CODE @RDSEC ( drv cylsec addr -- f )
     A 0x31 LDri, ( @RDSEC )
     0x28 RST,
     PUSHZ,
-;CODE
+EXX, ( unprotect BC ) ;CODE

blk/496

@@ -1,4 +1,4 @@
-CODE @WRSEC ( drv cylsec addr -- f )
+CODE @WRSEC ( drv cylsec addr -- f ) EXX, ( protect BC )
     HL POP,
     DE POP,
     BC POP,
@@ -6,7 +6,7 @@ CODE @WRSEC ( drv cylsec addr -- f )
     A 0x35 LDri, ( @WRSEC )
     0x28 RST,
     PUSHZ,
-;CODE
+EXX, ( unprotect BC ) ;CODE
 CODE @GET ( a -- c f )
     DE POP,
     chkPS,

blk/497

@@ -1,8 +1,8 @@
-CODE @PUT ( c a -- f )
+CODE @PUT ( c a -- f ) EXX, ( protect BC )
     DE POP,
     BC POP,
     chkPS,
     A 0x04 LDri, ( @PUT )
     0x28 RST,
     PUSHZ,
-;CODE
+EXX, ( unprotect BC ) ;CODE