Code Review Requested: BeatmapParser

Could someone with more expertise then me(everyone) please look at this code and let me know if it's sane?

Code:

; ==============================================================
; Reads a beatmap
; a0 - beatmap address
; d0 - beatmap data
; beatmap format:
; 76543210
; Bit 7 - if set it is the end of the beatmap
; Bit 6 - Not Used
; Bit 5 - Not Used
; Bit 4 - if set green note should be placed on board
; Bit 3 - if set red note should be placed on board
; Bit 2 - if set yellow note should be placed on board
; Bit 1 - if set blue note should be placed on board
; Bit 0 - if set orange note should be placed board
; ==============================================================
ReadBeatmap:
   move.b (a0), d0                                                             ; move beatmap data into d0
   btst #7, d0                                                                 ; test bit 7 to see if set
   bne.s @NotEndofBeatmap                                                      ; if not set skip
   moveq #64, d0                                                               ; clear all irrevelant bits
@NotEndofBeatmap:
   rts

I would test it myself but, i have no idea where to begin as i don't even know how to debug code. Any assistance in this matter would be greatly appreciated.

Signed,

Scorpion Illuminati

 

I havent done 68k in a while, but it looks like youre taking the byte at a0 and seeing if bit 7 is set to see if its the end. If its the end you throw decimal 64 in d0 and return, otherwise d0 has whatevers at offset a0 when you return. If thats what you want, thats what its doing