diff options
| -rw-r--r-- | main.asm | 39 |
1 files changed, 18 insertions, 21 deletions
@@ -11,7 +11,7 @@ ;;; Registers used: ;;; ;;; A7 = sp -;;; A6 = +;;; A6 = emulated PC ;;; A5 = instruction table base pointer ;;; A4 = bank 3 base ;;; A3 = bank 2 base @@ -59,9 +59,14 @@ PUTB MACRO ; 14 cycles, 4 bytes ;; Macro to read a word from main memory at register \1 ;; (unaligned). Puts the word read in \2. + ;; + ;; XXX deref + ;; + ;; <debrouxl> It decrements sp by 2, but stores the result at + ;; sp, not at 1(sp). So you essentially get a "free" shift + ;; left by 8 bits. Much faster than lsl.w / rol.w #8, at + ;; least. FETCHW MACRO - ;; XXX call deref - move.b 1(a6,\1.w),-(sp); 18/4 move.w (sp)+,\2 ; 8/2 move.b 0(a6,\1.w),\2 ; 14/4 @@ -125,12 +130,11 @@ FETCHBI MACRO ; 40 cycles, 14 bytes ;; Macro to read an immediate word (unaligned) into \1. FETCHWI MACRO ; 36 cycles, 12 bytes - ;; XXX use deref addq.w #2,d2 ; 4/2 - move.b -1(a6,d2.w),\1 ; 14/4 -;; XXX why not rol #8,\1 ?? (and then you would be able to use the same trick as in FETCHW). - rol.w #8,d2 ; 4/2 - move.b -2(a6,d2.w),\1 ; 14/4 + ;; See FETCHW for an explanation of this trick. + move.b 1(a6,d2.w),-(sp); 18/4 + move.w (sp)+,\1 ; 8/2 + move.b 0(a6,d2.w),\1 ; 14/4 ENDM ;; == Common Opcode Macros ========================================= @@ -265,7 +269,7 @@ emu_fetch: ;; space. ;; ;; Likely impossible to get rid of the clr - clr.w d0,d0 ; 4 cycles + clr.w d0 ; 4 cycles move.b (a4)+,d0 ; 8 cycles rol.w #5,d0 ; 16 cycles adjust to actual alignment jmp 0(a5,d0.w) ; 14 cycles @@ -1031,19 +1035,12 @@ emu_op_59: START emu_op_5a: ;; LD E,D - LOHI d5 - move.b d5,d1 - HILO d5 - move.b d1,d5 - DONE - - ;; Is this faster or slower? - - andi.w #$ff00,d5 - move.b d5,d1 - lsr #8,d1 - or.w d1,d5 + andi.w #$ff00,d5 ; 8/4 + move.b d5,d1 ; 4/2 + lsr #8,d1 ;22/2 + or.w d1,d5 ; 4/2 DONE + ;38/2 START emu_op_5b: |