Created Assembly program examples (markdown)

Assembly-program-examples.md

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+
+### Manhattan Distance
+This simple program calculates the [Manhattan distance](https://en.wikipedia.org/wiki/Taxicab_geometry) between the current position of the Cubot and another tile. 
+```assembly
+; Define constants
+LIDAR_HW equ 0x0003    ; HWID of the LiDAR
+HOLO_HW equ 0x0009     ; HWID of the Hologram projector
+
+; Data segment
+.data
+    
+counter: DW 0x0000     ; Counter global variable
+; The DW (Define word) directive writes the specified value(s), seperated by a
+; comma at assembly time. You can define a label before the directive to refer
+; to it by its name.
+
+; Code/executable segment
+.text
+    ; Program entry point
+    call getPos         ; Execute procedure
+    
+    PUSH 7              ; y2
+    PUSH 11             ; x2
+    call manhattanDist  ; Execute procedure
+    
+    TEST [counter], 1   ; Display 'ABCD' every other tick
+    JNZ counter_is_odd
+    MOV A, 0xABCD       
+counter_is_odd:
+
+    ADD [counter], 1    ; Increment counter
+    HWI HOLO_HW         ; Display the contents of A
+    BRK                 ; Exit program
+    
+;**************************************
+;* getPos()
+;* X = X pos
+;* Y = Y pos
+getPos:
+    PUSH A              ; Save A
+    MOV A, 0x0001       ; GET_POS
+    HWI LIDAR_HW        ; Send hardware interrupt to the LiDAR
+    POP A               ; Restore A
+    RET
+    
+
+;**************************************
+;* manhattanDist(x2,y2)
+;* A = Distance between (X,Y) and (x2,y2)      
+manhattanDist:
+    PUSH BP             ; Save previous stack frame
+    MOV BP, SP
+    
+    ; The old value of BP is at [BP + 0] 
+    ; The return address is at [BP + 1]
+    ; The x2 argument is at [BP + 2]
+    ; The y2 argument is at [BP + 3]
+
+    ; formula: |x1-x2| + |y1-y2|
+    SUB X, [BP + 2]     ; X = (X - x2)
+    
+    ; A fancy way to get the absolute value of X
+    MOV A, X            ; Copy X
+    SAR A, 15           ; Fill A with sign
+    XOR X, A            ; Do 'NOT X' if negative
+    SUB X, A            ; Do 'ADD X, 1' if negative
+    
+    SUB Y, [BP + 3]     ; Y = (Y - y2)
+    ; A simpler way to get the absolute value of Y
+    JNS y_is_positive
+    NEG Y               ; If Y was negative, it is NEG'd
+y_is_positive:
+
+    MOV A, X            ; A = |x1-x2|    
+    ADD A, Y            ; A = |x1-x2| + |y1-y2|
+    
+    POP BP              ; Restore the previous stack frame
+    RET 2               ; Return and POP our 2 arguments
+
+```