; AUTHOR: SEAN KESSLER                        DATE:04/17/1999
; PROGRAM: TALK.ASM
; PLATFORM:M68HC11
; FUNCTION:TEST SWI INSTRUCTION

EVENTCHAR    equ 000h
EVENTWORD    equ 001h
EVENTDWORD   equ 002h
EVENTVARCHAR equ 003h
EVENTREGS    equ 004h
EVENTEND     equ 0FFh

SCDR         equ 0102Fh     ; data register
SCSR         equ 0102Eh     ; status register
EEPROM       equ 0F800h     ; start of EEPROM 
RAM          equ 00000h     ; base of code
SWI          equ 0FFF6h     ; software interrupt vector lives here
REGS         equ 01000h     ; start of REGS
CONFIG       equ 0103Fh     ; CONFIG marks the end of REGS
BPROT        equ 01035h     ; BPROT
PPROG        equ 0103Bh     ; PPROG
MEMLOC       equ 80h        ; 80h,81h are scratch pad
STACK        equ RAM+0FFh   ; stack expands down from here
  org RAM                   ; base of code
BEGIN equ *
  lds STACK                 ; initialize the stack
START equ *                 ; start sync address
  bsr WRITEREGSEVENT        ; 
  bsr WRITEENDEVENT         ; 
  jmp START                 ; do it forever
WRITESTRING equ *
  rts
WRITEENDEVENT equ *         ; write end event to the SCI
  ldab EVENTEND             ; load the event type into register B
  bsr WRITECHAR             ; write the event to the SCI
  rts                       ; return to caller
WRITECHAREVENT equ *        ; write a character event to the SCI
  pshb                      ; save contents of register B 
  ldab EVENTCHAR            ; load event type into register B
  bsr WRITECHAR             ; write the event type to the SCI
  pulb                      ; restore contents of register B
  bsr WRITECHAR             ; write the event data to the SCI
  rts                       ; return to caller
WRITEREGSEVENT equ *        ; write the registers out to the SCI
  ldab EVENTREGS            ; load value of EVENTREGS into register B
  bsr WRITECHAR             ; send the value out to the SCI
  ldd REGS                  ; get address of REGS into register D   
CONTINUEREGS equ *          ; sync address
  psha                      ; save register A 
  pshb                      ; save register B
  xgdx                      ; exchange D with X (X has current address)
  ldab ix,00h               ; load byte at address in X to B register
  bsr WRITECHAR             ; send the byte out to the SCI     
  pulb                      ; restore register B
  pula                      ; restore register A
  addd 01h                  ; increment value in register D
  cpd CONFIG                ; compare this value to address of CONFIG register
  ble CONTINUEREGS          ; if it's less than or equal then keep going
  bsr WAITCHAR              ; wait for a character
  rts                       ; return to caller
WRITECHAR equ *             ; write character from B register to SCDR
  ldaa [SCSR]               ; get status into A register
  anda 80h                  ; check TDRE (transmit data register empty)
  beq WRITECHAR             ; keep trying until SCI is ready for character
  stab [SCDR]               ; write character from B register to SCDR
  rts                       ; return to caller
WRITEWORD equ *             ; write word in register D to the SCI
  psha                      ; save contents of register A
  bsr WRITECHAR             ; write contents of B (hi byte)
  pulb                      ; restore contents of register A into B
  bsr WRITECHAR             ; write contents of B (lo byte)
  rts                       ; return to caller
READCHAR equ *              ; read character from SCDR into B register
  psha                      ; save contents of register A
RDCLOOP equ *               ; wait loop
  ldaa [SCSR]               ; get status into A register
  anda 20h                  ; is RDRF set (indicates we have char)
  beq RDCLOOP               ; keep trying until RDRF is set
  ldab [SCDR]               ; load character into B register  
  pula                      ; save contents of register A
  rts                       ; return to caller
WAITCHAR equ *              ; wait for a character
  psha                      ; save contents of register A
  pshb                      ; save contents of register B
  bsr READCHAR              ; read a character into B register
  pulb                      ; restore contents of register B
  pula                      ; restore contents of register A
  rts                       ; return to caller