feat: modularized with lwtools build system

code/boot/src/serial.s

@@ -0,0 +1,45 @@
+; 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 OUTCHAR
+  EXPORT OUTSTR
+
+; Writes a char to the UART in non FIFO mode, preserves A.
+; @param b: char to write
+OUTCHAR
+  pshs a               ; Preserve A
+NOTREADY@
+  lda UART_LSR         ; if LSR.THRE == 1 then write
+  anda UARTF_LSR_THRE
+  bne NOTREADY@        ; Loop if UART not ready yet
+  stb UART_BUFR        ; Write char
+  puls a               ; Restore A
+  rts
+
+; Writes a null terminated string to the UART in non FIFO mode, clobbers A and
+; B.
+; @param x: null terminated string start address.
+OUTSTR
+  ldb 0,x              ; Get the next value from X
+  cmpb #$00            ; Make sure that we aren't at a terminator
+  beq END@
+  leax 1,x             ; Increment X for our next char
+NOTREADY@              ; Loop point for UART waiting
+  lda UART_LSR         ; Wait for UART to be ready
+  anda UARTF_LSR_THRE
+  bne NOTREADY@
+  stb UART_BUFR        ; Actually do our write
+  bra OUTSTR           ; Reset for the next char
+END@                   ; Jump point for end of routine
+  rts