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Example

	#include <p16f873.inc>        ; processor specific variable definitions

#define parse_state_offset 0x5

	cblock 0x20
	parse_state, parse_char
	endc

	cblock
	buffer	
	endc
	
push	macro x
	movlw x
	movwf INDF
	incf FSR, f
	endm
	
	movlw buffer
	movwf FSR
	push 'o'
	push 'f'
	push 'f'
;	push 's'
;	push 'e'
;	push 't'
	push'\0'
	
	movlw buffer - 1
	movwf FSR
start
	clrf parse_state
again
	incf FSR, f		;read next character
	movfw INDF	
	call parse
	movfw parse_state	;still initial state?
	skpnz
	 goto again
	sublw parse_state_offset-1 ;comand code?
	skpnc
	 goto match
	incfsz parse_state, w	;error?
	 goto again
	goto p_error
	
; ...
;

match	nop
	nop
	nop
	goto start
	
p_error	nop
	nop
	goto start
	


;-------------- keywords list ---------------------
; Case Sensitive
; Incomplete words match
; Whitespaces: ' ', '\t', 0x0D, 0x0A
; Delimiters: 0, ' ', '\t', 0x0D, 0x0A
;
; Keywords codes:
; 0x1	offset
; 0x2	echo
; 0x3	on
; 0x4	off

;***********************************************
; Simple parser for command names 
;
; Input:
;  w             next character in a string
;  parse_state   current state
; Output:
;  parse_state contains current state:
;     0 - initial state
;     1...(parse_state_offset-1) - command code
;     parse_state_offset...0xFE   - next state
;     0xFF - error (not matched)
; Temporary:
;  parse_char, parse_state
; Usage:
;	1)clrf parse_state
;	2)call parse with a new character
;	3)check parse_state and perform actions
;	4)repeat from 2)
; Note:
;  1) The parser takes one character as a look-ahead.
;  When a command name matches, parse_char contains
;  the first character AFTER the name. If it should
;  be checked also, initialize and call parse once more
;  with the same character first, then others as usually.
;  2) Size of state table is approximately 4 instructions
;  per each character of the total characters number
;  (e.g. total for commands "read" and "set" is 7,
;  i.e state table is about 21 instructions)
;
;***********************************************
parse
	movwf parse_char        ;save new character
	movfw parse_state       ;check if current state is zero
	skpz
	 goto parse2
	movfw parse_char        ;then skip whitespaces
	addlw	-' '		;accumulator == ' ' ?
	skpnz
	 retlw 0		;return if equal
	addlw	' ' - '\t'	;restore accumulator and check if equals '\t'
	skpnz
	 retlw 0		;return if equal
	addlw	'\t' - 0x0D	;restore accumulator and check if equals 0x0D
	skpnz
	 retlw 0		;return if equal
	addlw	0x0D - 0x0A	;restore accumulator and check if equals 0x0A
	skpnz
	 retlw 0		;return if equal
parse2
	call parse_table
	iorlw 0                 ;check if w == 0 (look ahead for delimiter succesful)
	skpz
	 movwf parse_state      ;store new state
	return
;***********************************************
; State Table
;
; Input:
;  parse_state -> current state + parse_state_offset
; Output:
;  w 	        -> new state + parse_state_offset
;
; Note
;  Zero parse_state means initial state
;***********************************************
parse_table
	movlw high(parse_table_start)
	movwf PCLATH
	movfw parse_state	;read current state
	skpnz			;is it inital?
	 goto parse_state0
	addlw -parse_state_offset-1 ;remove offset
;jump table with automatic block boundary workaround
	addlw low(parse_table_start)
	skpnc
	 incf PCLATH, f
	movwf PCL	;-> takeoff

parse_state_delimiter
;called from state table to check for end of name
	movwf parse_state
	movfw parse_char
	addlw	-0		;accumulator == 0 ?
	skpnz
	 retlw 0		;return if equal
	addlw	0 - ' '	;restore accumulator and check if equals ' '
	skpnz
	 retlw 0		;return if equal
	addlw	' ' - '\t'	;restore accumulator and check if equals '\t'
	skpnz
	 retlw 0		;return if equal
	addlw	'\t' - 0x0D	;restore accumulator and check if equals 0x0D
	skpnz
	 retlw 0		;return if equal
	addlw	0x0D - 0x0A	;restore accumulator and check if equals 0x0A
	skpnz
	 retlw 0		;return if equal
	retlw 0xFF

parse_table_start
;---------------- jump table start ----------------
	goto	parse_state1
	goto	parse_state2
	goto	parse_state3
	goto	parse_state4
	goto	parse_state5
	goto	parse_state6
	goto	parse_state7
	goto	parse_state8
	goto	parse_state9
	goto	parse_state10
	goto	parse_state11
;---------------- jump table end ------------------

;--------------- state table start ----------------
parse_state0
	movf	parse_char, w
	addlw	-'o'
	skpnz
	 retlw	0x6
	addlw	'o'-'e'
	skpnz
	 retlw	0xC
	retlw	0xFF
parse_state1
	movf	parse_char, w
	addlw	-'f'
	skpnz
	 retlw	0x7
	addlw	'f'-'n'
	skpnz
	 retlw	0x10
	goto	parse_state11
parse_state2
	movf	parse_char, w
	addlw	-'f'
	skpnz
	 retlw	0x8
	retlw	0xFF
parse_state3
	movf	parse_char, w
	addlw	-'s'
	skpnz
	 retlw	0x9
	movlw	0x4
	goto	parse_state_delimiter
parse_state4
	movf	parse_char, w
	addlw	-'e'
	skpnz
	 retlw	0xA
	goto	parse_state6
parse_state5
	movf	parse_char, w
	addlw	-'t'
	skpnz
	 retlw	0xB
parse_state6
	movlw	0x1
	goto	parse_state_delimiter
parse_state7
	movf	parse_char, w
	addlw	-'c'
	skpnz
	 retlw	0xD
	goto	parse_state10
parse_state8
	movf	parse_char, w
	addlw	-'h'
	skpnz
	 retlw	0xE
	goto	parse_state10
parse_state9
	movf	parse_char, w
	addlw	-'o'
	skpnz
	 retlw	0xF
parse_state10
	movlw	0x2
	goto	parse_state_delimiter
parse_state11
	movlw	0x3
	goto	parse_state_delimiter
;--------------- state table end ------------------

; Generated by www.piclist.com/cgi-bin/keyword.exe (version April 21, 2000)
; Fri Apr 21 09:47:08 2000 GMT
	end

See also:


file: /Techref/piclist/codegen/keyword_example.htm, 5KB, , updated: 2002/1/3 19:37, local time: 2018/10/16 10:49,
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