269 lines
4.9 KiB
NASM
269 lines
4.9 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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;
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; All numerical values in the Collapse OS shell are represented and parsed in
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; hexadecimal form, without prefix or suffix.
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; *** CONSTS ***
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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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; *** VARIABLES ***
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; Memory address that the shell is currently "pointing at" for peek and deek
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; operations. Set with seek.
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SHELL_MEM_PTR .equ SHELL_RAMSTART
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; Used to store formatted hex values just before printing it.
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SHELL_HEX_FMT .equ SHELL_MEM_PTR+2
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SHELL_RAMEND .equ SHELL_HEX_FMT+2
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; *** CODE ***
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shellInit:
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xor a
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ld (SHELL_MEM_PTR), a
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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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; check if the input buffer is full or ends in CR or LF. If it does,
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; prints it back and empty it.
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call aciaBufPtr
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cp 0
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jr z, shellLoop ; 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 ASCII_CR
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jr z, .do ; char is CR? do!
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cp ASCII_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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jr shellLoop
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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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jr shellLoop
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printcrlf:
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ld a, ASCII_CR
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call aciaPutC
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ld a, ASCII_LF
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call aciaPutC
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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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push hl
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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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; all right, we're almost ready to call the cmd. Let's just have DE
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; point to the cmd jump line.
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ld a, 4
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call addDE
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; Now, let's swap HL and DE because, welll because that's how we're set.
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ex hl, de ; HL = jump line, DE = cmd str pointer
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; Before we call our command, we want to set up the pointer to the arg
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; list. Normally, it's DE+5 (DE+4 is the space) unless DE+4 is null,
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; which means no arg.
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ld a, 4
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call addDE
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ld a, (DE)
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cp 0
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jr z, .noarg ; char is null? we have no arg
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inc de
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.noarg:
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; DE points to args, HL points to jump line. Ready to roll!
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call jumpHL
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.end:
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pop hl
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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 (in hex)
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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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ld hl, SHELL_HEX_FMT
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call fmtHexPair
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ld a, 2
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call printnstr
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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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; When these commands are called, DE points to the first character of the
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; command args.
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; Set memory pointer to the specified address (word).
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; Example: seek 01fe
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shellSeek:
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push af
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push de
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push hl
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ex de, hl
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call parseHexPair
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jr c, .error
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; z80 is little endian. in a "ld hl, (nn)" op, L is loaded from the
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; first byte, H is loaded from the second
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ld (SHELL_MEM_PTR+1), a
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inc hl
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inc hl
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call parseHexPair
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jr c, .error
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ld (SHELL_MEM_PTR), a
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jr .success
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.error:
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ld a, SHELL_ERR_BAD_ARGS
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call shellPrintErr
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jr .end
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.success:
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ld a, (SHELL_MEM_PTR+1)
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ld hl, SHELL_HEX_FMT
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call fmtHexPair
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ld a, 2
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call printnstr
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ld a, (SHELL_MEM_PTR)
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call fmtHexPair
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ld a, 2
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call printnstr
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call printcrlf
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.end:
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pop hl
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pop de
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pop af
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ret
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; peek byte where memory pointer points to any display its value. If the
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; optional numerical byte arg is supplied, this number of bytes will be printed
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;
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; Example: peek 2 (will print 2 bytes)
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shellPeek:
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push af
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push bc
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push de
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push hl
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ld b, 1 ; by default, we run the loop once
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ld a, (de)
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cp 0
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jr z, .success ; no arg? don't try to parse
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ex de, hl
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call parseHexPair
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jr c, .error
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cp 0
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jr z, .error ; zero isn't a good arg, error
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ld b, a ; loop the number of times specified in arg
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jr .success
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.error:
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ld a, SHELL_ERR_BAD_ARGS
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call shellPrintErr
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jr .end
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.success:
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ld hl, (SHELL_MEM_PTR)
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.loop: ld a, (hl)
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ex hl, de
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ld hl, SHELL_HEX_FMT
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call fmtHexPair
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ld a, 2
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call printnstr
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ex hl, de
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inc hl
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djnz .loop
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call printcrlf
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.end:
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pop hl
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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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; 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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