Transmission control is divided into three processes: the process of establishing, optional data and process status of the process
1, the process of establishing
Use the process of establishing a process to establish a transaction, the transaction is to establish a data output, compared with the output transactions of bulk transfers, there are several different:
The first is not the same token packet, the process of establishing the SETUP token packet
Followed by packet type, SETUP use only packet DATA0
Finally handshake, ACK equipment can only be used to answer (unless wrong, no answer), but can not use NAK or STALL to answer, that device must be established to receive data transactions
2, optional data process
A control data transmission may not process. If so, a process can contain data or multi-pen data transaction sum. Transmission control data transaction using the bulk transfer transmission bulk transaction is the same. Note that, in the course of the data, all the data transaction must be the same direction of transmission, once the data transfer direction is changed, it will assume the state into the process. First packet data DATA1 packet process must be, then after a correct transmission of each data packet DATA0 and DATA1 alternating between
3, the state of the process
State process is a sum of bulk transaction, and its transmission direction just in front of the stage opposite data. State only during packet DATA1
4, several examples of control transmission
