;--------------------------------------------------------------------------
;- Programmer: Zach Bunce, Kaioli Bessert, and Garrett Maxon
;- Date: 2/17/17
;-
;- Creates a firmware-based stack originating from 0xD0
;- Includes Push and Pop subroutines to allow for stack manipulation
;--------------------------------------------------------------------------

;--------------------------------------------------------------------------
;- Register Constants
;--------------------------------------------------------------------------
.DEF DATA = R30         ;Registers named to be easier to follow.
.DEF SP   = R31

;--------------------------------------------------------------------------
;-- .ORG used in code segment
;--------------------------------------------------------------------------
.CSEG
.ORG    0x10

;--------------------------------------------------------------------------
;-- Code Segment
;--------------------------------------------------------------------------
INIT:       MOV     SP, 0xD1    ;Sets the stack pointer register to 0xD1


S_PUSH: SUB SP, 0x01    ;Decrements the stack pointer
        ST  DATA, (R31) ;Pushes the data onto the stack

S_POP:      LD  DATA, (R31) ;Pops the data off the stack
        ADD SP, 0x01    ;Increments the stack pointer