A First Wristapp - Hello World

To illustrate, let us take our favorite C Program and figure out how to put it on the Datalink.  The first step in creating a wristapp is to decide on what the user interface will be.  You would think that with only 5 buttons, this would be an easy task, but in reality this can make or break a good application. For our application, we will have it so that when you first enter the app, it puts "HELLO WORLD MODE" on the screen.  If you press the PREV button, it will toggle to turning on all segments.  Pressing the PREV button will switch back to the "HELLO WORLD MODE".  The Next button will take you out of the app and the SET/NEXT buttons will not do anything.  Pressing the GLOW button will activate the indiglo light as expected.  Here's what the code would look like:

;Name: Hello World
;Version: HELLO
;Description: This is a simple Hello Program
;by John A. Toebes, VIII
;
;TIP:  Download your watch faster:  Download a WristApp once, then do not send it again.  It stays in the watch!
;HelpFile: watchapp.hlp
;HelpTopic: 106
            INCLUDE "WRISTAPP.I"
;
; (1) Program specific constants
;
FLAGBYTE	EQU  	$61
;   Bit 0 indicates that we want to show the segments instead of the message
;
START	EQU   *
;
; (2) System entry point vectors
L0110:  jmp	MAIN	; The main entry point - WRIST_MAIN
L0113:  rts             ; Called when we are suspended for any reason - WRIST_SUSPEND
	nop
      	nop
L0116:  rts             ; Called to handle any timers or time events - WRIST_DOTIC
	nop
	nop
L0119:	rts             ; Called when the COMM app starts and we have timers pending - WRIST_INCOMM
	nop
	nop
L011c:	rts             ; Called when the COMM app loads new data - WRIST_NEWDATA
	nop
        nop

L011f:	lda	STATETAB,X ; The state table get routine - WRIST_GETSTATE
        rts

L0123:  jmp	HANDLE_STATE0
        db  	STATETAB-STATETAB
;
; (3) Program strings
S6_HELLO:   timex6  "HELLO "
S6_WORLD:   timex6  "WORLD "
;
; (4) State Table
; (4) State Table
STATETAB:
        	db  	0
		db	EVT_ENTER,TIM_ONCE,0 	; Initial state
 	        db  	EVT_RESUME,TIM_ONCE,0   ; Resume from a nested app
        	db  	EVT_DNNEXT,TIM_ONCE,0	; Next button
        	db  	EVT_MODE,TIM_ONCE,$FF	; Mode button
        	db  	EVT_END
;
; (5) State Table 0 Handler
; This is called to process the state events.  We only see ENTER, RESUME, and DNNEXT events
;
HANDLE_STATE0:
 	  	bset	1,$8f			; Indicate that we can be suspended
         	lda	BTNSTATE		; Get the event
	    	cmp 	#EVT_DNNEXT             ; Did they press the next button?
		beq	DOTOGGLE		; Yes, toggle what we are displaying
CLEARIT         bclr    0,FLAGBYTE		; Start us in the show display state
REFRESH         brclr   0,FLAGBYTE,SHOWDISP	; Do we want to see the main display?
		jmp	SETALL			; No, just turn on all segments
SHOWDISP	jsr	CLEARALL		; Clear the display
		lda	#S6_HELLO-START         ; Get the offset for the first string
		jsr	PUT6TOP                 ; And send it to the top line
		lda	#S6_WORLD-START         ; Get the offset for the second string
		jsr	PUT6MID                 ; and put it on the middle line
		lda	#SYS8_MODE              ; Get the system offset for the 'MODE' string
		jmp	PUTMSGBOT               ; and put it on the bottom line
;
; (6) Our only real piece of working code...
DOTOGGLE	brset   0,FLAGBYTE,CLEARIT      ; If it is set, just jump to clear it like normal
		bset	0,FLAGBYTE              ; Already clear, so set it
		bra	REFRESH                 ; and let the refresh code handle it
;
; (7) This is the main initialization routine which is called when we first get the app into memory
;
MAIN:
		lda	#$c0		        ; We want button beeps and to indicate that we have been loaded
		sta	$96
	    	clr  	FLAGBYTE		; start with a clean slate
	    	rts

Now all of that code needs a little explaination.  As you can see from the numbers, we have 7 basic sections

1. Program specific constants - This is where you declare everything that you want to use.  As a Wristapp, you have only a limited amount of Ram (7 bytes to be specific) that you can store your stuff with, so be careful here.  
2. System entry point vectors - These are fixed and mandated for any Wristapp.  If there is more than one state, the JMP and db sequence is repeated for each state.
3. Program strings - In order to provide addressability to the strings, you need to put them immediately after the entry point vectors.
4. State Table(s) - This really tells the watch how we want to operate and what events we want to handle.  See The State Table for a more complete explaination of this.
5. State Table Handler(s) - These are called to process the events for a particular state.  Typically this is a LDA  BTNSTATE followed by a lot of CMP/Bcc instructions.  You also need to do the BSET 1,$8f at the start to allow the Wristapp to be suspendable.
6. Program Specific Code - The actual meat of the program.  In our case, we simply have to toggle a value.
7. Main Initialization routine - This is called once when the wristapp is first loaded.  We need to make sure that we set the appropriate bits in WRISTAPP_FLAGS.

Now that we have a basic program working.  Next Up:  Getting Input - Numbers