collapseos/parts/shell.asm

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; shell
;
; Runs a shell over a block device interface.
; Status: incomplete. As it is now, it spits a welcome prompt, wait for input
; and compare the first 4 chars of the input with a command table and call the
; appropriate routine if it's found, an error if it's not.
;
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; Commands, for now, are partially implemented.
;
; See constants below for error codes.
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;
; All numerical values in the Collapse OS shell are represented and parsed in
; hexadecimal form, without prefix or suffix.
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; *** DEFINES ***
; SHELL_GETC: Macro that calls a GetC routine
; SHELL_PUTC: Macro that calls a PutC routine
; SHELL_RAMSTART
; *** CONSTS ***
; number of entries in shellCmdTbl
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SHELL_CMD_COUNT .equ 4
; maximum number of bytes to receive as args in all commands. Determines the
; size of the args variable.
SHELL_CMD_ARGS_MAXSIZE .equ 3
; The command that was type isn't known to the shell
SHELL_ERR_UNKNOWN_CMD .equ 0x01
; Arguments for the command weren't properly formatted
SHELL_ERR_BAD_ARGS .equ 0x02
; Size of the shell command buffer. If a typed command reaches this size, the
; command is flushed immediately (same as pressing return).
SHELL_BUFSIZE .equ 0x20
; *** VARIABLES ***
; Memory address that the shell is currently "pointing at" for peek, load, call
; operations. Set with seek.
SHELL_MEM_PTR .equ SHELL_RAMSTART
; Used to store formatted hex values just before printing it.
SHELL_HEX_FMT .equ SHELL_MEM_PTR+2
; Places where we store arguments specifiers and where resulting values are
; written to after parsing.
SHELL_CMD_ARGS .equ SHELL_HEX_FMT+2
; Command buffer. We read types chars into this buffer until return is pressed
; This buffer is null-terminated and we don't keep an index around: we look
; for the null-termination every time we write to it. Simpler that way.
SHELL_BUF .equ SHELL_CMD_ARGS+SHELL_CMD_ARGS_MAXSIZE
SHELL_RAMEND .equ SHELL_BUF+SHELL_BUFSIZE
; *** CODE ***
shellInit:
xor a
ld (SHELL_MEM_PTR), a
ld (SHELL_BUF), a
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; print welcome
ld hl, .welcome
call printstr
ret
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.welcome:
.db "Collapse OS", ASCII_CR, ASCII_LF, "> ", 0
shellLoop:
; First, let's wait until something is typed.
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SHELL_GETC
; got it. Now, is it a CR or LF?
cp ASCII_CR
jr z, .do ; char is CR? do!
cp ASCII_LF
jr z, .do ; char is LF? do!
; Echo the received character right away so that we see what we type
SHELL_PUTC
; Ok, gotta add it do the buffer
; save char for later
ex af, af'
ld hl, SHELL_BUF
call findnull ; HL points to where we need to write
; A is the number of chars in the buf
cp SHELL_BUFSIZE
jr z, .do ; A == bufsize? then our buffer is full. do!
; bring the char back in A
ex af, af'
; Buffer not full, not CR or LF. Let's put that char in our buffer and
; read again.
ld (hl), a
; Now, write a zero to the next byte to properly terminate our string.
inc hl
xor a
ld (hl), a
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jr shellLoop
.do:
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call printcrlf
ld hl, SHELL_BUF
call shellParse
; empty our buffer by writing a zero to its first char
xor a
ld (hl), a
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ld hl, .prompt
call printstr
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jr shellLoop
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.prompt:
.db "> ", 0
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printcrlf:
ld a, ASCII_CR
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SHELL_PUTC
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ld a, ASCII_LF
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SHELL_PUTC
ret
; Parse command (null terminated) at HL and calls it
shellParse:
push af
push bc
push de
push hl
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push ix
ld de, shellCmdTbl
ld a, SHELL_CMD_COUNT
ld b, a
.loop:
ld a, 4 ; 4 chars to compare
call strncmp
jr z, .found
ld a, 7 + SHELL_CMD_ARGS_MAXSIZE
call addDE
djnz .loop
; exhausted loop? not found
ld a, SHELL_ERR_UNKNOWN_CMD
call shellPrintErr
jr .end
.found:
; we found our command. Now, let's parse our args.
ld a, 4
call addHL
; Now, let's have DE point to the argspecs
ld a, 4
call addDE
; We're ready to parse args
call shellParseArgs
cp 0
jr nz, .parseerror
ld hl, SHELL_CMD_ARGS
; Args parsed, now we can load the routine address and call it.
; let's have DE point to the jump line
ld a, SHELL_CMD_ARGS_MAXSIZE
call addDE
ld ixh, d
ld ixl, e
; Ready to roll!
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call callIX
jr .end
.parseerror:
ld a, SHELL_ERR_BAD_ARGS
call shellPrintErr
.end:
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pop ix
pop hl
pop de
pop bc
pop af
ret
; Print the error code set in A (in hex)
shellPrintErr:
push af
push hl
ld hl, .str
call printstr
ld hl, SHELL_HEX_FMT
call fmtHexPair
ld a, 2
call printnstr
call printcrlf
pop hl
pop af
ret
.str:
.db "ERR ", 0
; Parse arguments at (HL) with specifiers at (DE) into (SHELL_CMD_ARGS).
; (HL) should point to the character *just* after the name of the command
; because we verify, in the case that we have args, that we have a space there.
;
; Args specifiers are a series of flag for each arg:
; Bit 0 - arg present: if unset, we stop parsing there
; Bit 1 - is word: this arg is a word rather than a byte. Because our
; destination are bytes anyway, this doesn't change much except
; for whether we expect a space between the hex pairs. If set,
; you still need to have a specifier for the second part of
; the multibyte.
; Bit 2 - optional: If set and not present during parsing, we don't error out
; and write zero
;
; Sets A to nonzero if there was an error during parsing, zero otherwise.
; If there was an error during parsing, carry is set.
shellParseArgs:
push bc
push de
push hl
push ix
ld ix, SHELL_CMD_ARGS
ld a, SHELL_CMD_ARGS_MAXSIZE
ld b, a
xor c
.loop:
; init the arg value to a default 0
xor a
ld (ix), a
ld a, (hl)
; is this the end of the line?
cp 0
jr z, .endofargs
; do we have a proper space char?
cp ' '
jr z, .hasspace ; We're fine
; is our previous arg a multibyte? (argspec still in C)
bit 1, c
jr z, .error ; bit not set? error
dec hl ; offset the "inc hl" below
.hasspace:
; Get the specs
ld a, (de)
bit 0, a ; do we have an arg?
jr z, .error ; not set? then we have too many args
ld c, a ; save the specs for the next loop
inc hl ; (hl) points to a space, go next
call parseHexPair
jr c, .error
; we have a good arg and we need to write A in (IX).
ld (ix), a
; Good! increase counters
inc de
inc ix
inc hl ; get to following char (generally a space)
djnz .loop
; If we get here, it means that our next char *has* to be a null char
ld a, (hl)
cp 0
jr z, .success ; zero? great!
jr .error
.endofargs:
; We encountered our null char. Let's verify that we either have no
; more args or that they are optional
ld a, (de)
cp 0
jr z, .success ; no arg? success
bit 2, a
jr nz, .success ; if set, arg is optional. success
jr .error
.success:
xor a
jr .end
.error:
inc a
.end:
pop ix
pop hl
pop de
pop bc
ret
; *** COMMANDS ***
; When these commands are called, HL points to the first byte of the
; parsed command args.
; Set memory pointer to the specified address (word).
; Example: seek 01fe
shellSeek:
push af
push de
push hl
; z80 is little endian. in a "ld hl, (nn)" op, L is loaded from the
; first byte, H is loaded from the second.
ld a, (hl)
ld (SHELL_MEM_PTR+1), a
inc hl
ld a, (hl)
ld (SHELL_MEM_PTR), a
ld de, (SHELL_MEM_PTR)
ld hl, SHELL_HEX_FMT
ld a, d
call fmtHexPair
ld a, 2
call printnstr
ld a, e
call fmtHexPair
ld a, 2
call printnstr
call printcrlf
pop hl
pop de
pop af
ret
; peek byte where memory pointer points to any display its value. If the
; optional numerical byte arg is supplied, this number of bytes will be printed
;
; Example: peek 2 (will print 2 bytes)
shellPeek:
push af
push bc
push de
push hl
ld a, (hl)
cp 0
jr nz, .arg1isset ; if arg1 is set, no need for a default
ld a, 1 ; default for arg1
.arg1isset:
ld b, a
ld hl, (SHELL_MEM_PTR)
.loop: ld a, (hl)
ex hl, de
ld hl, SHELL_HEX_FMT
call fmtHexPair
ld a, 2
call printnstr
ex hl, de
inc hl
djnz .loop
call printcrlf
.end:
pop hl
pop de
pop bc
pop af
ret
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; Load the specified number of bytes (max 0xff) from IO and write them in the
; current memory pointer (which doesn't change). For now, we can only load from
; SHELL_GETC, but a method of selecting IO sources is coming, making this
; command much more useful.
; Control is returned to the shell only after all bytes are read.
;
; Example: load 42
shellLoad:
push af
push bc
push hl
ld a, (hl)
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ld b, a
ld hl, (SHELL_MEM_PTR)
.loop: SHELL_GETC
ld (hl), a
inc hl
djnz .loop
.end:
pop hl
pop bc
pop af
ret
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; Calls the routine where the memory pointer currently points. This can take two
; parameters, A and HL. The first one is a byte, the second, a word. These are
; the values that A and HL are going to be set to just before calling.
; Example: run 42 cafe
shellCall:
push af
push hl
push ix
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; Let's recap here. At this point, we have:
; 1. The address we want to execute in (SHELL_MEM_PTR)
; 2. our A arg as the first byte of (HL)
; 2. our HL arg as (HL+1) and (HL+2)
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; Ready, set, go!
ld a, (SHELL_MEM_PTR)
ld ixl, a
ld a, (SHELL_MEM_PTR+1)
ld ixh, a
ld a, (hl)
ex af, af'
inc hl
ld a, (hl)
exx
ld h, a
exx
inc hl
ld a, (hl)
exx
ld l, a
ex af, af'
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call callIX
.end:
pop ix
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pop hl
pop af
ret
; Format: 4 bytes name followed by SHELL_CMD_ARGS_MAXSIZE bytes specifiers,
; followed by 3 bytes jump. fill names with zeroes
shellCmdTbl:
.db "seek", 0b011, 0b001, 0
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jp shellSeek
.db "peek", 0b101, 0, 0
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jp shellPeek
.db "load", 0b001, 0, 0
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jp shellLoad
.db "call", 0b101, 0b111, 0b001
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jp shellCall