Populate repository from old progress; massive cleanup and fixes

src/serial.s

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+; CHIBI PC-09 Prototype #1 Boot ROM -- Serial Driver
+; Copyright (c) 2024-2025 Amber Zeller, Gale Faraday
+; Licensed under MIT
+
+  INCLUDE "hardware.inc"
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;; Serial UART Driver
+;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+  SECTION SERIAL
+
+  EXPORT INITUART
+  EXPORT POUTCHAR
+  EXPORT POUTZSTR
+
+; Initializes the UART with LCR settings and a BAUD rate from DIVISORS.
+; ACCA: Index of the divsor to use in DIVISORS
+; ACCB: Settings for LCR
+INITUART
+  ldx #DIVISORS ; Get DIVISORS base addr
+  asla          ; Shift left to *2 the index in order to iter over words.
+  pshs b        ; Save B
+  ldd a,x       ; Get divisor into D
+  sta UART_DLM  ; Write divisor MSB
+  stb UART_DLL  ; Write divisor LSB
+  lda UARTF_FCR_FE|UARTF_FCR_RFR|UARTF_FCR_XFR ; FIFO disable and clear
+  sta UART_FCR
+  lda #0
+  sta UART_IER  ; Polled mode
+  sta UART_MCR  ; Reset DTR, RTS
+  rts
+
+; Prints a character in polled non-FIFO mode (INITUART state).
+; ACCA: char to write
+POUTCHAR
+  pshs a       ; Preserve char
+NEXTC@
+  lda UART_LSR ; Wait until LSR.THRE == 1 then write char
+  bita UARTF_LSR_THRE
+  beq NEXTC@
+  puls a       ; Restore char
+  sta UART_THR ; Write char
+  rts
+
+; Prints a null terminated string in polled non-FIFO mode (INITUART state).
+; X: start of zstring
+POUTZSTR
+  pshs a,b     ; Preserve A and B
+NEXTC@
+  ldb 0,x      ; Get next char from X
+  cmpb #$00    ; Make sure that we aren't at a terminator
+  leax 1,x     ; Increment X for next char. we inc here to save bytes if the
+               ; next string is adjacent.
+  beq END@
+NOTREADY@
+  lda UART_LSR ; Wait until LSR.THRE == 1 then write char
+  bita UARTF_LSR_THRE
+  beq NOTREADY@
+  stb UART_THR ; Write char
+  bra NEXTC@   ; Iter to next char
+END@
+  puls b,a     ; Restore A and B
+  rts
+
+DIVISORS
+  fdb $0900 ; 50 baud
+  fdb $0600 ; 75 baud
+  fdb $0417 ; 110 baud
+  fdb $0359 ; 134.5 baud
+  fdb $0300 ; 150 baud
+  fdb $0180 ; 300 baud
+  fdb $00C0 ; 600 baud
+  fdb $0060 ; 1200 baud
+  fdb $0040 ; 1800 baud
+  fdb $0030 ; 2400 baud
+  fdb $0020 ; 3600 baud
+  fdb $0018 ; 4800 baud
+  fdb $0010 ; 7200 baud
+  fdb $000C ; 9600 baud
+  fdb $0006 ; 19200 baud