stage0/stage0/stage0_monitor.s

154 lines
4.3 KiB
ArmAsm

; Copyright (C) 2016 Jeremiah Orians
; This file is part of stage0.
;
; stage0 is free software: you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, either version 3 of the License, or
; (at your option) any later version.
;
; stage0 is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with stage0. If not, see <http://www.gnu.org/licenses/>.
;; R14 will be storing our condition
;;
;; R13 will be a stack pointer. It will be zero
;; on the start, and the stack grows up.
;; This means that when stack is used, the
;; first instructions of this program will be
;; overwritten. But because this is initialization
;; code, it is already not used at the time.
;; And the stack usage is fixed - there is only one CALL
;; instruction in this file
;;
;; R2 Is our holder.
;; It holds the first nybble of the byte till the second iteration
;;
;; R12 Is our toggle. It is initialized to zero on start.
;; When non-zero, it means that we are processing the second nybble
;;
;; R8 will hold zero. It is initialized to zero on start.
:start
;; Prepare often-used values that will be held in registers
LOADUI R15 0xF ; Set R15 to 0xF
LOADUI R11 0x1101 ; R11 will hold 0x1101
;; Prep TAPE_01
MUX R0 R15 R11 R8 ; 0x1100 = ((0x1101 & ~0xF) | (0 | 0xF))
FOPEN_WRITE
;; Prep TAPE_02
COPY R0 R11 ; 0x1101
FOPEN_WRITE
:loop
FALSE R1 ; Read from tty
FGETC ; Read a Char
CMPSKIPI.NE R0 13 ; Replace all CR
LOADUI R0 10 ; WIth LF
FPUTC ; Display the Char to User
;; Check for Ctrl-D
CMPSKIPI.NE R0 4
JUMP @finish
;; Check for EOF
JUMP.NP R0 @finish
;; Write out unprocessed byte
COPY R1 R11 ; Write to TAPE_02
FPUTC ; Print the Char
;; Convert byte to nybble
CALLI R13 @hex ; Convert it
;; Get another byte if nonhex
JUMP.NP R0 @loop ; Don't use nonhex chars
;; Deal with the case of second nybble
JUMP.NZ R12 @second_nybble ; Jump if toggled
;; Process first byte of pair
AND R2 R0 R15 ; Store First nibble
TRUE R12 ; Flip the toggle
JUMP @loop
;; Combined second nybble in pair with first
:second_nybble
SL0I R2 4 ; Shift our first nibble
AND R0 R0 R15 ; Mask out top
ADD R0 R0 R2 ; Combine nibbles
;; Writeout and prepare for next cycle
FALSE R12 ; Flip the toggle
; Write the combined byte
MUX R1 R15 R11 R8 ; To TAPE_01
FPUTC
JUMP @loop ; Try to get more bytes
:hex
;; Deal with line comments starting with #
CMPUI R14 R0 35
JUMP.E R14 @ascii_comment
;; Deal with line comments starting with ;
CMPUI R14 R0 59
JUMP.E R14 @ascii_comment
;; Deal with all ascii less than '0'
CMPUI R14 R0 48
JUMP.L R14 @ascii_other
;; Deal with '0'-'9'
CMPUI R14 R0 57
JUMP.LE R14 @ascii_num
;; Deal with all ascii less than 'A'
CMPUI R14 R0 65
JUMP.L R14 @ascii_other
;; Deal with 'A'-'F'
CMPUI R14 R0 70
JUMP.LE R14 @ascii_high
;; Deal with all ascii less than 'a'
CMPUI R14 R0 97
JUMP.L R14 @ascii_other
;; Deal with 'a'-'f'
CMPUI R14 R0 102
JUMP.LE R14 @ascii_low
;; Ignore the rest
JUMP @ascii_other
:ascii_num
SUBUI R0 R0 48
RET R13
:ascii_low
SUBUI R0 R0 87
RET R13
:ascii_high
SUBUI R0 R0 55
RET R13
:ascii_other
TRUE R0
RET R13
:ascii_comment
FALSE R1 ; Read from tty
FGETC ; Read another char
CMPSKIPI.NE R0 13 ; Replace all CR
LOADUI R0 10 ; WIth LF
FPUTC ; Let the user see it
CMPUI R14 R0 10 ; Stop at the end of line
COPY R1 R11 ; Write to TAPE_02
FPUTC ; The char we just read
JUMP.NE R14 @ascii_comment ; Otherwise keep looping
JUMP @ascii_other
:finish
MUX R0 R15 R11 R8 ; Close TAPE_01
FCLOSE
COPY R0 R11 ; Close TAPE_02
FCLOSE
HALT