; CHIBI PC-09 Prototype #1 Boot ROM
; (Copyright (c) 2024 Amber Zeller

; UART registers
UART = $7F00

; When DLAB = 0
BUFR = UART  ; TX/RX Buffer (Read for RX, Write for TX)
IER = UART+1 ; Interrupt Enable Register
IIR = UART+1 ; Interrupt Enable Register (Upon Read)
; When DLAB = 1
DLL = UART   ; Divisor Latch (LSB)
DLM = UART+1 ; Divisor Latch (MSB)

FCR = UART+2 ; FIFO Control Register (Upon Write)
LCR = UART+3 ; Line Control Register
MCR = UART+4 ; MODEM Control Register
LSR = UART+5 ; Line Status Register
MSR = UART+6 ; MODEM Status Register
SCR = UART+7 ; Scratch Register (Not for control just spare RAM)

;  SECTION code

  org $8000

RESET:
  ; UART Setup
  lda %11000001 ; 8n1 serial, enable DLAB
  sta LCR

  lda $00       ; Set divisor to 12 (9600 baud)
  sta DLL
  lda $0C
  sta DLM

  lda %11000000 ; 8n1 serial, disable DLAB
  sta LCR

  lda %01000000 ; Enable RTS
  sta MCR

  lda 'H        ; send H
  STA BUFR

;  ENDSECTION

;  SECTION vectors
  org $FFF0
  ; Reset/Interrupt Vectors
  fdb  $0000 ; Reserved
  fdb  $0000 ; SWI3
  fdb  $0000 ; SWI2
  fdb  $0000 ; FIRQ
  fdb  $0000 ; IRQ
  fdb  $0000 ; SWI
  fdb  $0000 ; NMI
  fdb  RESET ; Reset
;  ENDSECTION