请教马老师BASCOM-AVR利用AVR-DOS库读写SD卡，U盘，CF卡等外部存储的原理
最近在BASCOM的官方网站上看到一个用BASCOM程序写的MP3资料，里面的程序不是很懂http://cache.amobbs.com/bbs_upload782111/files_30/ourdev_563294OM1RNA.jpg
实物图 (原文件名:MP3BOARD.jpg)
http://cache.amobbs.com/bbs_upload782111/files_30/ourdev_563295SPPUAH.jpg
原理图 (原文件名:MP3SCH.jpg)
程序如下，希望马老师能帮忙解释一下
'///////////////////////////////////////////////////////////////////////////////
'///////////////////////////////////////////////////////////////////////////////
'
' MP_3_PLAYER with VS1001k FOR MP3.FILES FORMAT Name 8.3 FAT16 AVR-DOS 5.5
' data 14-06-2007 versione BASCOM 1.8.11.3AVR-DOS 5.5
' written by GIOVANNI DE LUCA
' HTTP://delucagiovanni.interfree.it robot applications and others
' HTTP://WWW.LNS.INFN.IT nuclear phisics applications
' HTTP://www.youtube.com/tubincolo my video mobile-robots
' deluca@lns.infn.it my e-mail
' to control it's used serial port com1 and pul "UP" to change songs
' to make test I used 64Mb MMC with 20 songs in the MMC
' but I thing that it's possible read bigger MMC memory without problem
'
'///////////////////////////////////////////////////////////////////////////////
'///////////////////////////////////////////////////////////////////////////////
$prog &HFF , &H4F , &HC5 , &HFF 'FUSE BITS generated
$regfile = "M128def.dat" 'IT'S POSSIBLE USE DIFFERENT AVR-CHIPS
$crystal = 14745600 'BUT this NOT TESTED
$baud = 115200
'-------------------------------------------------------------------------------
Config Timer1 = Timer , Prescale = 64
Config Clock = Soft
Enable Interrupts
Enable Timer1
Enable Urxc 'abilita rs232
On Timer1 Timer_1
On Urxc Rs_232 'salto per rs232
Config Date = Dmy , Separator = .
'-------------------------------------------------------------------------------
Avanti Alias Ping.0
Led Alias Portg.1
Vs_miso Alias Pinc.0
Vs_mosi Alias Portc.1
Vs_clock Alias Portc.2
Xcs Alias Portc.3
Xreset Alias Portc.4
Dreq Alias Pinc.5
Bsync Alias Portc.6
'-------------------------------------------------------------------------------
Config Avanti = Input 'pulsante avanti
Config Led = Output 'led
Config Vs_miso = Input 'serial input vs-1001
Config Vs_mosi = Output 'serial out vs-1001
Config Vs_clock = Output 'serial clock vs-1001
Config Xcs = Output 'VS Chip Select
Config Xreset = Output 'VS Reset
Config Dreq = Input 'VS Data Request
Config Bsync = Output 'VS Stream Request
'-------------------------------------------------------------------------------
Declare Sub Vs_init()
Declare Sub Soft_reset()
Declare Sub Vs_write(byval Vs_address As Byte , Byval Data1 As Byte , Byval Data2 As Byte)
Declare Function Vs_read(byval Vs_address As Byte) As Word
Declare Sub Send_mp3(byval Filename As String)
'-------------------------------------------------------------------------------
Const Vs_rd = &B0000_0011 'Write command vs1001
Const Vs_wr = &B0000_0010 'Read commandvs1001
Const Vs_mode = 0
Const Vs_status = 1
Const Vs_clockf = 3
Const Vs_decode_time = 4
Const Vs_audata = 5
Const Vs_volume = 11
'-------------------------------------------------------------------------------
Dim B As Byte
Dim I As Integer
Dim J As Long
Dim Curbyte As Long
Dim S As String * 20
Dim Sample_rate As Word
Dim Bit_rate As Word
Dim Is_stereo As Word
Dim Audata As Word
Dim Filename As String * 11
Dim Mmc_data(512) As Byte '512 byte
Dim Tempo_new As Word
Dim Tempo_old As Word
Dim Flag_read As Bit
Dim Flag_play As Bit
Dim Comando As String * 10
Dim Mode_low As Byte
Dim Mode_hig As Byte
Dim Volume As Word
Dim Volume_low As Byte
Dim Volume_hig As Byte
'-------------------------------------------------------------------------------
$Include "Config_MMC.bas" 'include mmc
If Gbdriveerror <> 0 Then End
$Include "Config_AVR-DOS.BAS" 'include avr-dos
B = Initfilesystem(1) 'init file system
If B <> 0 Then Print "Errore MMC" 'se errore
'-------------------------------------------------------------------------------
Bsync = 0
Xreset = 0
Xcs = 1
Portg.0 = 1 'res pull up
Flag_play = 0 'sta suonando ?
Flag_read = 1 'gia letto ?
'-------------------------------------------------------------------------------
'--------------------------PROGRAM START -------------------------------------
'-------------------------------------------------------------------------------
Print "Dir *.mp3" 'dir mp3
'-------------------------------------------------------------------------------
'---------------------- crea una lista dei brani mp3 presenti sulla MMC --------
'-------------------------------------------------------------------------------
Open "Lista.txt" For Output As #9 'create file.list in MMC
S = Dir( "*.mp3")
While Len(s) > 0
Print S ; "" ; Filedate() ; "" ; Filetime() ; "" ; Filelen()
Print #9 , S 'memorizza la lista
S = Dir()
Wend
Close #9
'-------------------------------------------------------------------------------
Print "VS1001 Init"
Vs_init 'reset hardware e inizializza
'-------------------------------------------------------------------------------
'--------------------------- MAIN PROGRAMM -------------------------------------
'-------------------------------------------------------------------------------
Do
Open "Lista.txt" For Input As #9 'OPEN LA LISTA
While Eof(#9) = 0
Line Input #9 , S 'READ filename Mp3
Call Send_mp3(s) 'play mp3
Wend
Close #9
Loop
End
'-------------------------------------------------------------------------------
'---------------------------- TIMER 1 ------------------------------------------
'-------------------------------------------------------------------------------
Timer_1:
If Bsync = 0 And Flag_play = 1 And Flag_read = 1 Then'per leggere inforamzioni
Flag_read = 0
Audata = Vs_read(vs_audata)
Sample_rate = Audata And &H1E00
Rotate Sample_rate , Right , 9
Bit_rate = Audata And &H1FF
Is_stereo = Audata And &H8000
Rotate Is_stereo , Right , 15
Print Sample_rate ; "," ; Bit_rate ; " Kbs," ; Is_stereo 'print informations
End If
If Bsync = 0 And Flag_play = 1 And Flag_read = 0 Then
Tempo_new = Vs_read(vs_decode_time)
If Tempo_new <> Tempo_old Then Print Tempo_new ; " Sec"
Tempo_old = Tempo_new
End If
Return
'-------------------------------------------------------------------------------
'---------------------- RS 232 -------------------------------------------------
'-------------------------------------------------------------------------------
Rs_232:
Comando = Inkey()
If Comando = "1" Then
Mode_low.7 = 1
Bsync = 0
Vs_write Vs_mode , &H0 , Mode_low 'no loudness
End If
If Comando = "2" Then
Mode_low.7 = 0
Bsync = 0
Vs_write Vs_mode , &H0 , Mode_low 'loudness
End If
If Comando = "3" Then
Mode_low.1 = 0
Bsync = 0
Vs_write Vs_mode , &H0 , Mode_low 'play normale
End If
If Comando = "4" Then
Mode_low.1 = 1
Bsync = 0
Vs_write Vs_mode , &H0 , Mode_low 'play veloce
End If
If Comando = "5" And Volume_low < 250 Then
Volume_hig = Volume_hig + 5
Volume_low = Volume_low + 5
Bsync = 0
Vs_write Vs_volume , Volume_hig , Volume_low 'volume down
End If
If Comando = "6" And Volume_low > 0 Then
Volume_hig = Volume_hig - 5
Volume_low = Volume_low - 5
Bsync = 0
Vs_write Vs_volume , Volume_hig , Volume_low 'volume up
End If
Comando = ""
Return
'-------------------------------------------------------------------------------
'------------------------------ MP3 SUBROUTINES --------------------------------
'-------------------------------------------------------------------------------
Function Vs_read(byval Vs_address As Byte) As Word
Xcs = 0 'Xcs low
B = Vs_rd
Shiftout Vs_mosi , Vs_clock , B , 1
Shiftout Vs_mosi , Vs_clock , Vs_address , 1
B = 0
Shiftin Vs_miso , Vs_clock , B , 1
Vs_read = B
Shift Vs_read , Left , 8
B = 0
Shiftin Vs_miso , Vs_clock , B , 1
Vs_read = Vs_read + B
Xcs = 1 'Xcs high
End Function
'-------------------------------------------------------------------------------
'-------------------------------- WRITE ROUTINE --------------------------------
'-------------------------------------------------------------------------------
Sub Vs_write(byval Vs_address As Byte , Byval Data1 As Byte , Byval Data2 As Byte)
Xcs = 0
B = Vs_wr
Shiftout Vs_mosi , Vs_clock , B , 1
Shiftout Vs_mosi , Vs_clock , Vs_address , 1
Shiftout Vs_mosi , Vs_clock , Data1 , 1
Shiftout Vs_mosi , Vs_clock , Data2 , 1
Xcs = 1
End Sub
'-------------------------------------------------------------------------------
'------------------------------- RESETTA E INIZILIZZA --------------------------
'-------------------------------------------------------------------------------
Sub Vs_init()
Xreset = 0
Waitms 5
Xreset = 1
Waitms 10
Do : Led = Dreq : Loop Until Dreq = 1
Vs_write Vs_mode , &H0 , &H4 'reset
Do : Led = Dreq : Loop Until Dreq = 1
Mode_low.7 = 1
Vs_write Vs_mode , &H0 , Mode_low 'bass
Do : Led = Dreq : Loop Until Dreq = 1
Vs_write Vs_clockf , &H0 , &H0 'clockf24,xx MHz
Do : Led = Dreq : Loop Until Dreq = 1
Vs_write Vs_volume , &H0 , &H0 'volume =0 massimo
End Sub
'-------------------------------------------------------------------------------
'--------------------------- SOFT RESET VS1001 ---------------------------------
'-------------------------------------------------------------------------------
Sub Soft_reset
Do : Led = Dreq : Loop Until Dreq = 1 'wait Dreq
Vs_write Vs_mode , &H0 , &H4 'reset
End Sub
'-------------------------------------------------------------------------------
'---------------------------- SEND FILE MP3 ------------------------------------
'-------------------------------------------------------------------------------
Sub Send_mp3(byval Filename As String)
Print "Play : " ; Filename
Soft_reset 'resetta vs1001
Flag_read = 1 'per leggere una volta sample rate etc
Flag_play = 0 'inizia a leggere dopo che è stato letto il primo pacchetto
Open Filename For Binary As #10 'apri il file mp3 e play song
Do : Led = Dreq : Loop Until Dreq = 1 'wait Dreq
While Eof(#10) = 0
Get #10 , Mmc_data(1) , , 512 'preleva 512 byte
Do : Led = Dreq : Loop Until Dreq = 1 'wait Dreq
For I = 1 To 16
For J = 1 To 32
Bsync = 1
Shiftout Vs_mosi , Vs_clock , Mmc_data(curbyte) , 1
Bsync = 0
Incr Curbyte
Next J
Do : Led = Dreq : Loop Until Dreq = 1 'wait Dreq
Next I 'first 32
Curbyte = 1 'after 1616x32=512 byte
If Avanti = 0 Then Goto Esci 'pulsante up
Flag_play = 1 'playing primo pacchetto
Wend
Esci:
Flag_play = 0 'stop play
Close #10
For I = 1 To 2048 'send 2048 zeros to clear buffer
B = 0
Shiftout Vs_mosi , Vs_clock , B , 1 'send 2048 byte
Next I
Print "MP3 End" 'end song
Waitms 100 'aspetta 100
End Sub
'------------------------------------------------------------------------------- 如果不学习掌握基本的知识，比如SPI接口、SD卡协议，MP3格式等，当然是看不懂代码了。 首先要感谢马老师白忙之中回复我的帖子，我用BASCOM写单片机也有3年左右了，最近看到这个程序，觉得它有研究的价值，之所以不懂才来这请教马老师，希望马老师给我讲讲
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