6502 command stream player, part 6

preparing NES test player

src/asm/6502/nes/nes.i

@@ -0,0 +1,23 @@
+; this is a definition file for a NES ROM.
+
+.MEMORYMAP
+DEFAULTSLOT 1
+; 2KB RAM
+SLOT 0 START $0000 SIZE $800
+; 32KB ROM
+SLOT 1 START $8000 SIZE $8000
+.ENDME
+
+.ROMBANKMAP
+BANKSTOTAL 2
+; iNES header
+BANKSIZE $10
+; program ROM data
+BANKSIZE $8000
+BANKS 1
+; character ROM data
+
+.ENDRO
+
+.BANK 1 SLOT 1
+.ORGA $8000

src/asm/6502/nes/test.s

@@ -0,0 +1,6 @@
+; command stream player test - NES version
+; NES because it's what I am most familiar with, besides Atari 2600
+
+.include "nes.i"
+
+main:

src/asm/6502/stream.s

@@ -194,18 +194,19 @@ fcsOptPlaceholder:
   rts
 
 fcsCallI:
-  jsr fcsPushCall
   ; get address
   jsr fcsReadNext
-  tay
+  pha
   jsr fcsReadNext
+  pha
   ; ignore next two bytes
   jsr fcsIgnoreNext
   jsr fcsIgnoreNext
-  ; a has high byte
+  jsr fcsPushCall
-  ; y has low byte
+  pla
-  sty chanPC,x
   sta chanPC+1,x
+  pla
+  sta chanPC,x
   rts
 
 fcsOffWait:
@@ -221,21 +222,44 @@ fcsFullCmd:
   rts
 
 fcsCall:
-  jsr fcsPushCall
   ; get address
   jsr fcsReadNext
-  tay
+  pha
   jsr fcsReadNext
-  ; a has high byte
+  pha
-  ; y has low byte
+  jsr fcsPushCall
-  sty chanPC,x
+  pla
   sta chanPC+1,x
+  pla
+  sta chanPC,x
   rts
 
+; push channel PC to stack
 fcsPushCall:
+  lda chanStackPtr,x
+  tay
+  lda chanPC,x
+  sta fcsGlobalStack,y
+  iny
+  lda chanPC+1,x
+  sta fcsGlobalStack,y
+  iny
+  tya
+  sta chanStackPtr,x
   rts
 
+; retrieve channel PC from stack
 fcsRet:
+  lda chanStackPtr,x
+  tay
+  dey
+  lda fcsGlobalStack,y
+  sta chanPC+1,x
+  dey
+  lda fcsGlobalStack,y
+  sta chanPC,x
+  tya
+  sta chanStackPtr,x
   rts
 
 fcsJump: