debug.asm

这项工程将让您把自己的MP3播放器平台

	.title	Debug Functions
	.sbttl	(C) 2005 Spare Time Gizmos.  All rights reserved.

;++
;
; Copyright (C) 2005 by Spare Time Gizmos.  All rights reserved.
;
; This file is part of the Spare Time Gizmos' MP3 Player firmware.
;
; Thisfirmware 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 2 of the License, or (at your option) any later
; version.
;
; This program 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
; this program; if not, write to the Free Software Foundation, Inc., 59 Temple
; Place, Suite 330, Boston, MA  02111-1307  USA
; 
; DESCRIPTION:
;   This module contains routines to initialize and reset the watch dog timer
; (WDT), as well as serial port routines used for debug I/O using the standard
; 8051's internal UART.  The only reason we need these special routines for
; serial I/O rather than the standard C library functions is so that the WDT
; can be reset.  Otherwise the WDT would time out while we're typing long
; strings or waiting for input.
;
; WARNING:
;   The serial port uses timer 1 for baud rate generation!
;
; REVISION HISTORY:
; dd-mmm-yy     who     description
; 15-May-05	RLA	New File
; 03-Jul-05	DJA 	ported to SDCC/ASX8051
;--

	.module	 DEBUG
	.optsdcc -mmcs51 --model-small
	.radix	 d
	.include "player.inc"	

	.globl	_InitializeDebugSerial, __getkey, _putchar
	.globl	_InitializeWDT, _ResetWDT

	.area CSEG	(CODE)


;
;++
; void InitializeWDT (void)
;
; DESCRIPTION:
;   This routine will initialize the standard P89C51Rx2 watch dog timer.
; The WDT used in the Atmel AT89C51Rx2 chips is compatible with the Philips
; parts and will work with this routine.  Unfortunately the WDT in the
; Philips 87C66x parts is NOT compatible with this code.
;
;   The watch dog timer is _disabled_ by a reset and remains disabled
; until it is enabled by this routine.  Once enabled, the WDT cannot
; be disabled again except by another hardware reset!
;
; NOTE:
;-
_InitializeWDT:
; Not yet implemented...
	RET


;++
; void ResetWDT (void)
;
; DESCRIPTION:
;   This routine will reset the watch dog timer.  Needless to say it must be
; called more often than the WDT timeout interval.
;
; NOTE:
;--
_ResetWDT:
; Not yet implemented...
        RET


;
;   The serial port baud rate is generated by timer 1 in 8 bit auto reload
; mode, and the rate is determined by:
;
;  T1RELOAD = 256 - ( CPU_CLOCK / (16*12*BAUD_RATE) ) [SMOD == 1]
;  T1RELOAD = 256 - ( CPU_CLOCK / (32*12*BAUD_RATE) ) [SMOD == 0]
;
;   NOTE: On the Philips P89CC66x family parts with the 6 clocks per cycle option,
; all baud rates are doubled!

T1RELOAD = 0xFB	; 19,200 bps on P89C66x with SMOD==0 and 18.432MHz clock	


;++
; void InitializeDebugSerial (void)
;
; DESCRIPTION:
;   This routine will initialize the 8051's internal UART.  This interface
; is used only for debugging purposes, so the baud rate is fixed at 9600. 
; Timer 1 is used to generate the baud rate clock, and interrupts are _not_
; enabled for the UART!
;--
_InitializeDebugSerial:
	MOV	SCON, #0x52	; select mode 1 - 8 bit UART, set REN, TI
	ANL	TMOD, #0x0F	; set up timer 1 as the baud rate clock
	ORL	TMOD, #0x20 	; select mode 2 - 8 bit auto reload
	MOV	TH1, #T1RELOAD	; set the divisor for the baud rate
	ANL	PCON, #0x3F	; always use SMOD=0 for the baud rate
	SETB	TR1		; and start the timer running
	SETB	TI		; enable the transmitter
;;	SETB	REN		; and enable the receiver
	RET			; and we're done



;++
; char _getkey (void)
;
; DESCRIPTION:
;   This function waits for a character to be received on the 8051's serial
; port.  The character received is returned as the function's value.
;
; REGISTERS: (determined by the SDCC compiler!)
;    DPL	-> character/byte returned from terminal
;
; NOTE:
;   The only reason we need this function instead of the standard C51 library
; equivalent is that this one keeps the WDT running!
;--
__getkey:
	ACALL	_ResetWDT	; don't let the WDT run out on us!
	JNB	RI, __getkey	; but otherwise wait for any key
	MOV	DPL, SBUF	; there's something there now - read it
	CLR	RI		; and enable the receiver for next time
	RET			; all done


;++
; void putchar (char c)
;
; DESCRIPTION:
;   This function transmits the character c to the 8051's serial port.  If the
; port is still busy transmitting the last character, it will wait.  If the
; character printed is a newline ('\n'), then a carriage return will be added
; automatically.
;
; REGISTERS: (determined by the SDCC compiler!)
;    DPL	-> character to output (c)
;
; NOTE:
;   The only reason we need this function instead of the standard C51 library
; equivalent is that this one keeps the WDT running!
;   Unlike the C51 library equivalent, this function does not handle XON or
; XOFF.
;   In the case of a newline, it actually outputs <LF> <CR> rather than the
; more usual <CR> <LF>.  This doesn't seem to cause any harm...
;--
_putchar:
	ACALL	_ResetWDT	; keep the WDT going while we wait
	JNB	TI, _putchar	; wait for the transmitter to be idle
	MOV	SBUF, DPL	; send this byte to the terminal
	CLR	TI		; and start the transmitter going
	MOV	A, DPL		; (can't compare DPL)
	CJNE	A,#0x0A, putret	; did we just print a newline ("\n") ?
	MOV	DPL, #0x0D	; yes - send a carriage return too
	AJMP	_putchar	; ...
putret:	RET			; otherwise we're done
;