fat.s

采用Atmeag162单片机来制作的U盘程序源码

	.module Fat.c
	.area text(rom, con, rel)
	.dbfile D:\AvrUSB\Fat.c
	.dbfunc e BPB_Local _BPB_Local fi
;        NumFATs -> R10
;        FATSz16 -> R20,R21
;     RootEntCnt -> R22,R23
;     BytsPerSec -> R12,R13
;          value -> R20,R21
	.even
_BPB_Local::
	xcall push_gset4
	sbiw R28,2
	.dbline -1
	.dbline 11
; #include <iom162v.h>
; #include <macros.h>
; #include <stdio.h>
; #include <string.h>
; 
; #include "Flash.h"
; #include "Fat.h"
; 
; extern unsigned char PageBuf[512];
; unsigned int BPB_Local()
; {
	.dbline 14
;    unsigned int  BytsPerSec,RootEntCnt, FATSz16,value;
;    unsigned char NumFATs;   
;    ReadPage(0,0,PageBuf);
	ldi R24,<_PageBuf
	ldi R25,>_PageBuf
	std y+1,R25
	std y+0,R24
	clr R18
	clr R19
	clr R16
	clr R17
	xcall _ReadPage
	.dbline 15
;    if(PageBuf[510]!=0x55&&PageBuf[511]!=0xAA)return 16;
	lds R24,_PageBuf+510
	cpi R24,85
	breq L2
	lds R24,_PageBuf+511
	cpi R24,170
	breq L2
	.dbline 15
	ldi R16,16
	ldi R17,0
	xjmp L1
L2:
	.dbline 16
;    BytsPerSec=PageBuf[12]*256+PageBuf[11];
	lds R18,_PageBuf+12
	clr R19
	ldi R16,256
	ldi R17,1
	xcall empy16s
	movw R12,R16
	lds R2,_PageBuf+11
	clr R3
	add R12,R2
	adc R13,R3
	.dbline 17
;    NumFATs=PageBuf[16];
	lds R10,_PageBuf+16
	.dbline 18
;    RootEntCnt=PageBuf[18]*256+PageBuf[17]; 
	lds R18,_PageBuf+18
	clr R19
	ldi R16,256
	ldi R17,1
	xcall empy16s
	movw R22,R16
	lds R2,_PageBuf+17
	clr R3
	add R22,R2
	adc R23,R3
	.dbline 19
;    FATSz16=PageBuf[23]*256+PageBuf[22]; 
	lds R18,_PageBuf+23
	clr R19
	ldi R16,256
	ldi R17,1
	xcall empy16s
	movw R20,R16
	lds R2,_PageBuf+22
	clr R3
	add R20,R2
	adc R21,R3
	.dbline 20
;    value=FATSz16*NumFATs*(BytsPerSec/512);
	ldi R18,9
	ldi R19,0
	movw R16,R12
	xcall lsr16
	movw R2,R16
	mov R18,R10
	clr R19
	movw R16,R20
	xcall empy16s
	movw R18,R2
	xcall empy16s
	movw R20,R16
	.dbline 21
;    value+=RootEntCnt/16;//(32/512)
	movw R2,R22
	lsr R3
	ror R2
	lsr R3
	ror R2
	lsr R3
	ror R2
	lsr R3
	ror R2
	add R20,R2
	adc R21,R3
	.dbline 22
;    return (value+1)/32;
	ldi R18,5
	ldi R19,0
	movw R16,R20
	subi R16,255  ; offset = 1
	sbci R17,255
	xcall lsr16
	.dbline -2
L1:
	adiw R28,2
	xcall pop_gset4
	.dbline 0 ; func end
	ret
	.dbsym r NumFATs 10 c
	.dbsym r FATSz16 20 i
	.dbsym r RootEntCnt 22 i
	.dbsym r BytsPerSec 12 i
	.dbsym r value 20 i
	.dbend