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USB Mass storage Device协议即海量存储设备协议适用于硬盘,U盘等大容量存储设备。协议使用的接口端点有BulkIn、BulkOut和Interrupt端点。该设备类又包含6个独立的子类以及3种传输协议。
bInterfaceSubClass | 命令集 | 描述 |
---|---|---|
01h | RBC | 通常,FlashDevice使用RBC,事实上所有大容量存储设备都可使用RBC |
02h | SFF-8020i,MMC-2(ATAPI) | 适用硬盘,C/DVD |
03h | QIC-157 | 适用磁盘 |
04h | UFI | 适用软盘 |
05h | SFF-8070i | 适用移动存储设备 |
06h | SCSI | 目前绝大多数USB Mass Storage设备都使用SCSI指令集 |
bInterfaceProtocol | 协议实现 | 描述 |
00h | Control/Bulk/Interrupt protocol(含命令完成中断) | USB海量存储类CBI传输,只适用于全速 |
01h | Control/Bulk/Interrupt protocol(不含命令完成中断) | USB海量存储类CBI传输,只适用于全速 |
50h | Bulk-Only传输 | Bulk-Only传输 |
本文仅介绍SCSI子类下Bulk-Only的传输协议,我们手中的U盘就是遵循SCSI协议的。要知道U盘不仅仅是USB设备,它还是一种存储设备,类似硬盘,USB协议本身没有定义对存储设备操作的指令,所以需要通过SCSI来完成读写等操作。关于此类设备的描述符不再赘述,需要注意的是在interface描述符中:
CBW(Command Block Wrapper)的长度为31个字节,具体定义如下图:
CSW的长度为13个字节,是对应CBW指令的状态返回,它指示了上一条指令执行是否成功,具体定义如下:
SCSI(Small Computer System Interface)的指令集有很多,参考http://en.wikipedia.org/wiki/SCSI_command ,其中USB Mass Storage主要用到的指令有:
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
04H |
|||||||
1 |
LUN |
FmtData |
CmpList |
Defect List Format |
||||
2 |
Vendor-specific |
|||||||
3 |
Interleave (MSB) |
|||||||
4 |
Interleave (LSB) |
|||||||
5—6 |
保留 |
|||||||
7 |
Parameter List Length (MSB) |
|||||||
8 |
Parameter List Length (LSB) |
|||||||
|
|
Parameter List
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
Reserved |
|||||||
1 |
FOV |
Extend(0) |
DCRT(1) |
SingleTrack |
Reserved |
Immediate |
Side |
|
2 |
Defect List Length (MSB) (0) |
|||||||
3 |
Defect List Length (LSB) (8) |
|||||||
4—7 |
MSB Number of Blocks |
|||||||
8 |
Reserved |
|||||||
9—11 |
MSB Block Length |
注意:Number of Block和Block Length的值要与Read Format Capacity的返回相匹配
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
12H |
|||||||
1 |
LUN |
Reserved |
EVPD(0) |
|||||
2 |
Page Code |
|||||||
3 |
Reserved |
|||||||
4 |
MSB Allocation Length |
|||||||
5—11 |
Reserved |
标准INQUIRY返回数据
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
Reserved |
Peripheral Device Type |
||||||
1 |
RMB |
Reserved |
||||||
2 |
ISO Version(00h) |
ECMA Version(00h) |
ANSI Version (00h) |
|||||
3 |
Reserved |
Response Data Format |
||||||
4 |
Additional Length (31) |
|||||||
5—7 |
Reserved |
|||||||
8—15 |
Vendor Information |
|||||||
16—31 |
Product Identification |
|||||||
32—35 |
Product Revision Level |
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|||
0 |
55H |
||||||||||
1 |
LUN |
PF |
Reserved |
SP |
|||||||
2—6 |
Reserved |
||||||||||
7—8 |
MSB Parameter List Length |
||||||||||
9—11 |
Reserved |
MODE SENSE
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
5AH |
|||||||
1 |
LUN |
Reserved |
DBD |
Reserved |
||||
2 |
PC |
Page Code |
||||||
3—6 |
Reserved |
|||||||
7—8 |
MSB Parameter List Length |
|||||||
9—11 |
Reserved |
PREVENT-ALLOW MEDIUM REMOVAL
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
0 |
1EH |
||||||||
1 |
LUN |
Reserved |
|||||||
2-3 |
Reserved |
||||||||
4 |
Reserved |
Prevent |
|||||||
5-11 |
Reserved |
Prevent:置1表示禁止移除设备
READ(10)
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
28H |
|||||||
1 |
LUN |
DPO(0) |
FUA(0) |
Reserved |
RelAdr(0) |
|||
2-5 |
Logical Block Address |
|||||||
6 |
Reserved |
|||||||
7—8 |
MSB Transfer Length |
|||||||
9—11 |
Reserved |
READ(12) A8H的Transfer Length为32位,从6-9字节
READ CAPACITY
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
0 |
25H |
||||||||
1 |
LUN |
Reserved |
RelAdr(0) |
||||||
2-5 |
Logical Block Address(0) |
||||||||
6-7 |
Reserved |
||||||||
8 |
Reserved |
PMI(0) |
|||||||
9—11 |
Reserved |
此命令返回8个字节,0-3表示最后一个逻辑块的地址,4-7表示每个逻辑块的长度
READ FORMAT CAPACITIES
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
23H |
|||||||
1 |
LUN |
Reserved |
||||||
2-6 |
Reserved |
|||||||
7-8 |
Allocation Length |
|||||||
9-11 |
Reserved |
Allocation Length:定义了HOST能够接收的最大格式化数据长度
REQUEST SENSE
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
03H |
|||||||
1 |
LUN |
Reserved |
||||||
2-3 |
Reserved |
|||||||
4 |
Allocation Length |
|||||||
5-11 |
Reserved |
Allocation Length:定义了HOST能够接收的最大格式化数据长度
HOST每发送完一个命令,device都会通过REQUEST SENSE返回该条指令的执行结果,sense data的长度为18字节。
标准sense data
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
|
0 |
Valid |
Error Code (70h) |
|||||||
1 |
Reserved |
||||||||
2 |
Reserved |
Sense Key |
|||||||
3-6 |
Information |
||||||||
7 |
Additional Sense Length (0AH) |
||||||||
8-11 |
Reserved |
||||||||
12 |
Additional Sense Code (Mandatory) |
||||||||
13 |
Additional Sense Code Qualifier (Mandatory) |
||||||||
14-17 |
Reserved |
Valid:表示Information域是否有效
Information:表示出错的逻辑块地址
SEEK
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
2BH |
|||||||
1 |
LUN |
Reserved |
||||||
2-5 |
Logical Block Address |
|||||||
6-11 |
Reserved |
SEND DIAGNOSTIC
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
1DH |
|||||||
1 |
LUN |
PF |
Reserved |
SelfTest |
DefOfl |
UnitOfl |
||
2-11 |
Reserved |
SelfTest:置1表示执行默认的自检,置0表示执行特殊的自检
TEST UNIT READY
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
00H |
|||||||
1 |
LUN |
Reserved |
||||||
2-11 |
Reserved |
VERIFY
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
2FH |
|||||||
1 |
LUN |
DPO(0) |
Reserved |
ByteChk(0) |
RelAdr(0) |
|||
2-5 |
Logical Block Address |
|||||||
6 |
Reserved |
|||||||
7-8 |
Verification Length |
|||||||
9-11 |
Reserved |
Logical Block Address:验证的起始地址
Verification Length:验证数据的长度
WRITE(10)
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
2AH |
|||||||
1 |
LUN |
DPO(0) |
FUA(0) |
Reserved |
RelAdr(0) |
|||
2-5 |
Logical Block Address |
|||||||
6 |
Reserved |
|||||||
7-8 |
Transfer Length |
|||||||
9-11 |
Reserved |
WRITE(12) AAH的Transfer Length为32位,从6-9字节
WRITE AND VERIFY
Bit Byte |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
0 |
2EH |
|||||||
1 |
LUN |
DPO(0) |
Reserved |
ByteChk (0) |
RelAdr(0) |
|||
2-5 |
Logical Block Address |
|||||||
6 |
Reserved |
|||||||
7-8 |
Transfer Length |
|||||||
9-11 |
Reserved |
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原文地址:http://www.cnblogs.com/heiyue/p/4377238.html