.export count_set_bits
;;********************************************************************************
;; @function Initialize the PS2 keyboard
;; @details
;;  Count the number of set bits in Y.
;;  
;; @modifies: A, X, Y
;; @returns Y: The number of set bits in the byte
;;********************************************************************************
.proc count_set_bits
    ldx #8
    ldy #0  ; number of set bits
@loop:
    dex 
    beq @done
    ror
    bcc @loop
@set:
    iny
    bra @loop
@done:
    rts
.endproc