_startup.a51

这是用python语言写的一个数字广播的信号处理工具包。利用它

;;; -*- asm -*-
;;;
;;; Copyright 2003,2004 Free Software Foundation, Inc.
;;; 
;;; This file is part of GNU Radio
;;; 
;;; GNU Radio 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, or (at your option)
;;; any later version.
;;; 
;;; GNU Radio 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 GNU Radio; see the file COPYING.  If not, write to
;;; the Free Software Foundation, Inc., 51 Franklin Street,
;;; Boston, MA 02110-1301, USA.

    
;;; The default external memory initialization provided by sdcc is not
;;; appropriate to the FX2.  This is derived from the sdcc code, but uses 
;;; the FX2 specific _MPAGE sfr.


	;; .area XISEG   (XDATA)  ; the initialized external data area
	;; .area XINIT   (CODE)	  ; the code space consts to init XISEG
	.area XSEG    (XDATA)	  ; zero initialized xdata
	.area USBDESCSEG (XDATA)  ; usb descriptors

	
	.area CSEG    (CODE)

	;; sfr that sets upper address byte of MOVX using @r0 or @r1
	_MPAGE	=	0x0092

__sdcc_external_startup::
	;; This system is now compiled with the --no-xinit-opt 
	;; which means that any initialized XDATA is handled
	;; inline by code in the GSINIT segs emitted for each file.
	;; 
	;; We zero XSEG and all of the internal ram to ensure 
	;; a known good state for uninitialized variables.

;	_mcs51_genRAMCLEAR() start
	mov	r0,#l_XSEG
	mov	a,r0
	orl	a,#(l_XSEG >> 8)
	jz	00002$
	mov	r1,#((l_XSEG + 255) >> 8)
	mov	dptr,#s_XSEG
	clr     a
	
00001$:	movx	@dptr,a
	inc	dptr
	djnz	r0,00001$
	djnz	r1,00001$
	
	;; We're about to clear internal memory.  This will overwrite
	;; the stack which contains our return address.
	;; Pop our return address into DPH, DPL
00002$:	pop	dph
	pop	dpl
	
	;; R0 and A contain 0.  This loop will execute 256 times.
	;; 
	;; FWIW the first iteration writes direct address 0x00,
	;; which is the location of r0.  We get lucky, we're 
	;; writing the correct value (0)
	
00003$:	mov	@r0,a
	djnz	r0,00003$

	push	dpl		; restore our return address
	push	dph

	mov	dpl,#0		; indicate that data init is still required
	ret