; Latest WDC 65C51 has a bug - Xmit bit in status register is stuck on
; IRQ driven transmit is not possible as a result - interrupts are endlessly triggered
; Polled I/O mode also doesn't work as the Xmit bit is polled - delay routine is the only option
; The following delay routine kills time to allow W65C51 to complete a character transmit
; 0.523 milliseconds required loop time for 19,200 baud rate
; MINIDLY routine takes 524 clock cycles to complete - X Reg is used for the count loop
; Y Reg is loaded with the CPU clock rate in MHz (whole increments only) and used as a multiplier
;
DELAY_6551   PHY      ;Save Y Reg
         PHX      ;Save X Reg
DELAY_LOOP   LDY   #2    ;Get delay value (clock rate in MHz 2 clock cycles)
;
MINIDLY   LDX   #$68      ;Seed X reg
DELAY_1      DEX         ;Decrement low index
         BNE   DELAY_1   ;Loop back until done
;
         DEY         ;Decrease by one
         BNE   MINIDLY   ;Loop until done
         PLX         ;Restore X Reg
         PLY         ;Restore Y Reg
DELAY_DONE   RTS         ;Delay done, return
;


nmi
    rti 
irq
    rti

__reset
    ; Init STACK
   LDX #$FF
   TXS

    ; Init acia
    ; 19,200 baud, 8-bits, 1 stop bit
   LDA #$1F
   STA $4403 ;ACIA_control
   LDA #$0A
   STA $4402 ;ACIA_command

LOOP
   LDA $4401 ;ACIA_status.. <-- not sure if the status reg must be read?
   ;AND #$10 ; <-- Doesn't work on the WDC, since the bit is stuck, delay instead.
   ;BEQ LOOP
    JSR DELAY_6551
   LDA #$41
   STA $4400 ;ACIA_data
    ;JSR DELAY_6551
   JMP LOOP

; Interrupt vectors   
.ORGA $FFFA
.dw nmi
.dw __reset
.dw irq

                lda     #%00011111              ; 8 bits, 1 stop bit, 19200 baud
                sta     ACIA_CTL
                lda     #%11001001              ; No parity, no interrupt
                sta     ACIA_CMD
                lda     ACIA_RXD                ; Clear receive buffer

INIT_6551
               SEI   ;Disable Interrupts
               STZ   SIOSTAT   ;write to status reg, reset 6551
               STZ   STTVAL   ;zero status pointer (Page Zero pointer)
               LDX   #$02   ;Get count of 2
INIT_6551L
               LDA   LOAD_6551-1,X    ;Get Current config parameters for 6551
               STA   SIOBase+1,X   ;Write to the 6551
               DEX   ;Decrement count
               BNE   INIT_6551L   ;Loop back until done
               CLI   ;Re-enable Interrupts
               RTS   ;Return to caller
;