222 lines
3.5 KiB
NASM
222 lines
3.5 KiB
NASM
; shell
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;
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; Runs a shell over an asynchronous communication interface adapter (ACIA).
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; for now, this unit is tightly coupled to acia.asm, but it will eventually be
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; more general than that.
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; Status: incomplete. As it is now, it spits a welcome prompt, wait for input
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; and compare the first 4 chars of the input with a command table and call the
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; appropriate routine if it's found, an error if it's not.
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;
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; Commands, for now, are dummy.
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;
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; See constants below for error codes.
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; *** CONSTS ***
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CR .equ 0x0d
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LF .equ 0x0a
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; number of entries in shellCmdTbl
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SHELL_CMD_COUNT .equ 2
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; The command that was type isn't known to the shell
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SHELL_ERR_UNKNOWN_CMD .equ 0x01
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; Arguments for the command weren't properly formatted
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SHELL_ERR_BAD_ARGS .equ 0x02
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; *** CODE ***
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shellInit:
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; print prompt
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ld hl, .prompt
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call printstr
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call printcrlf
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ret
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.prompt:
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.db "Collapse OS", 0
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shellLoop:
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call chkbuf
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jr shellLoop
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; print null-terminated string pointed to by HL
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printstr:
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push af
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push hl
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.loop:
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ld a, (hl) ; load character to send
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or a ; is it zero?
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jr z, .end ; if yes, we're finished
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call aciaPutC
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inc hl
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jr .loop
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.end:
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pop hl
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pop af
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ret
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printcrlf:
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ld a, CR
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call aciaPutC
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ld a, LF
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call aciaPutC
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ret
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; check if the input buffer is full or ends in CR or LF. If it does, prints it
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; back and empty it.
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chkbuf:
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call aciaBufPtr
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cp 0
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ret z ; BUFIDX is zero? nothing to check.
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cp ACIA_BUFSIZE
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jr z, .do ; if BUFIDX == BUFSIZE? do!
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; our previous char is in BUFIDX - 1. Fetch this
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dec hl
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ld a, (hl) ; now, that's our char we have in A
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inc hl ; put HL back where it was
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cp CR
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jr z, .do ; char is CR? do!
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cp LF
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jr z, .do ; char is LF? do!
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; nothing matched? don't do anything
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ret
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.do:
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; terminate our string with 0
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xor a
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ld (hl), a
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; reset buffer index
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ld (ACIA_BUFIDX), a
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; alright, let's go!
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ld hl, ACIA_BUF
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call shellParse
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ret
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; Compares strings pointed to by HL and DE up to A count of characters. If
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; equal, Z is set. If not equal, Z is reset.
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strncmp:
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push bc
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push hl
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push de
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ld b, a
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.loop:
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ld a, (de)
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cp (hl)
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jr nz, .end ; not equal? break early
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inc hl
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inc de
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djnz .loop
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.end:
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pop de
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pop hl
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pop bc
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; Because we don't call anything else than CP that modify the Z flag,
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; our Z value will be that of the last cp (reset if we broke the loop
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; early, set otherwise)
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ret
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; add the value of A into DE
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addDE:
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add a, e
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jr nc, .end ; no carry? skip inc
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inc d
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.end:
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ld e, a
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ret
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; jump to the location pointed to by HL. This allows us to call HL instead of
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; just jumping it.
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jumpHL:
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jp hl
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ret
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; Parse command (null terminated) at HL and calls it
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shellParse:
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push af
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push bc
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push de
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ld de, shellCmdTbl
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ld a, SHELL_CMD_COUNT
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ld b, a
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.loop:
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ld a, 4 ; 4 chars to compare
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call strncmp
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jr z, .found
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ld a, 6
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call addDE
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djnz .loop
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; exhausted loop? not found
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ld a, SHELL_ERR_UNKNOWN_CMD
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call shellPrintErr
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jr .end
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.found:
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ld a, 4
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call addDE
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ex hl, de
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call jumpHL
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ex hl, de
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.end:
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pop de
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pop bc
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pop af
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ret
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; Print the error code set in A (doesn't work for codes > 9 yet...)
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shellPrintErr:
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push af
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push hl
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ld hl, .str
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call printstr
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; ascii for '0' is 0x30
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add a, 0x30
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call aciaPutC
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call printcrlf
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pop hl
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pop af
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ret
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.str:
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.db "ERR ", 0
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; *** COMMANDS ***
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shellSeek:
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ld hl, .str
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call printstr
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ret
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.str:
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.db "seek called", CR, LF, 0
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shellPeek:
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ld hl, .str
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call printstr
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ret
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.str:
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.db "peek called", CR, LF, 0
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; Format: 4 bytes name followed by 2 bytes jump. fill names with zeroes
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shellCmdTbl:
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.db "seek"
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jr shellSeek
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.db "peek"
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jr shellPeek
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