; Serial Port Driver
; Developed by Charles Childers and Christopher Brannon
; -----------------------------------------------------
; * Released into the public domain *
; -----------------------------------------------------
; Port Addresses
;  $3F8  =  COM1
;  $2F8  =  COM2
;  $3E8  =  COM3
;  $2E8  =  COM4
; -----------------------------------------------------
; Baud Rates
;  $01 = 115,200
;  $02 =  57,600
;  $03 =  38,400
;  $06 =  19,200
;  $0C =   9,600
;  $18 =   4,800
;  $30 =   2,400
; -----------------------------------------------------
port = $3f8     ; Default to COM1
baud = $03 ; Default to 38,400 baud

; al = byte to send
write_serial:                        ;
   mov dx, port + 5        ; LSR
       xchg ah, al             ;
.a:    in al, dx               ;
   test al, $20            ; Bit 5 of LSR is set when the
      jz .a                   ; transmit buffer is empty
  xchg ah, al             ;
   mov dx, port            ;
   out dx, al              ;
ret                                ;

init_serial:                       ;
   mov dx, port + 1        ; Turn off interrupts
       mov al, 0               ;
   out dx, al              ;
   mov al, $80             ; Turn DLAB on
      mov dx, port + 3        ;
   out dx, al              ;
   mov dx, port            ; Set baud rate
     mov al, baud            ; baud rate (38,400 is default)
     out dx, al              ;
   mov dx, port + 1        ; Set baud rate
     mov al, 0               ;
   out dx, al              ;
   mov dx, port + 3        ; 8 bits, no parity, 1 stop bit
     mov al, $03             ;
   out dx, al              ;
   mov dx, port + 4        ; Turn on DTR, RTS, and OUT2
        mov al, $0b             ;
   out dx, al              ;
   mov dx, port + 2        ; Enable FIFO
       mov al, $c7             ;
   out dx, al              ;
ret                                ;

; returns al = byte read
read_serial:                   ;
   xor eax, eax            ;
   mov dx, port + 5        ; LSR
.a:        in al, dx               ;
   test al, 1              ;
   jz .a                   ;
   mov dx, port            ;
   in al, dx               ;
ret                                ;