in,out,setup数据类型以及四种传输类型的区别

12ycli

楼主，我在看USB的书，看完之后发现又有其他的见解了。
Bulk、Control、Interrupt和Isochronous这些叫Transaction（事务），IN、OUT、Setup这些叫transfer。一个transfer通常包括多个Transaction。

Each transfer consists of one or more transactions, and each transaction
inturn consists of one, two, or three packets.

The  three  transaction  types  are  defined  by  their  purpose  and  direction  of
data  flow.  Setup  transactions  send  control-transfer  requests  to  a  device.
OUT transactions send other data or status information to the device. IN
transactions send data or status information to the host.

The USB specification defines a transaction as the delivery of service to an
endpoint. Service in this case can mean either the host’s sending information
to the device, or the host’s requesting and receiving information from the
device.

Each  transaction  includes  identifying,  error-checking,  status,  and  control
information as well as any data to be exchanged. A complete transfer may
take place over multiple frames or microframes, but a transaction must com-
plete uninterrupted. No other communication on the bus can break into the
middle of a transaction. Devices thus must be able to respond quickly with
requested data or status information in a transaction. Device firmware typi-
cally configures, or arms, an endpoint to respond to received packets, and
the hardware responds to the packets when they arrive.

A  transfer  with  a  small  amount  of  data  may  require  just  one  transaction.
Other transfers require multiple transactions with a portion of the data in
each.

12ycli

多谢楼主