【正文】 re than one input or output transaction structure, pliance and batch send the same protocol rules. All the data phase of the transaction must have the same direction (that is, all input or all output). In the data phase, the amount of data to be sent, and its direction is specified in the establishment phase. If the amount of data exceeds the previously identified data packet size, the data in support of the largest packet size of the number of transactions to be sent (input or output). Any remaining data as a residual in the final transaction is sent. Control of the state of transmission phase is the last one operation sequence. State phase at a relatively earlier stage of the data to characterize the changes in flow direction, and always use the DATA1 PID. For example, if the data phase transaction constituted by the output, the state is a single input transaction. If the control sequence is no data transmission phase, then it is by the establishment phase and the subsequent transaction by the input stages, consisting of the state. Interrupt transactions may consist of IN or OUT transfers. Upon receipt of an IN token, a function may return data, NAK, or STALL. If the endpoint has no new interrupt information to return (., no interrupt is pending), the function returns a NAK handshake during the data phase. If the Halt feature is set for the interrupt endpoint, the function will return a STALL handshake. If an interrupt is pending, the function returns the interrupt information as a data packet. The host, in response to receipt of the data packet, issues either an ACK handshake if data was received errorfree or returns no handshake if the data packet was received corrupted. Such endpoints use multiple transactions in a microframe as defined in that section. Each transaction for a highbandwidth. When an endpoint is using the interrupt transfer mechanism for actual interrupt data, the data toggle protocol must be followed. This allows the function to know that the data has been received by the host and the event condition may be cleared. This “guaranteed” delivery of events allows the function to only send the interrupt information until it has been received by the host rather than having to send the interrupt data every time the function is polled and until the USB System Software clears the interrupt condition. 3 Data Toggle Synchronization and Retry The USB provides a mechanism to guarantee data sequence synchronization between data transmitter and receiver across multiple transactions. This mechanism provides a 11 means of guaranteeing that the handshake phase of a transaction was interpreted correctly by both the transmitter and receiver. Synchronization is achieved via use of the DATA0 and DATA1 PIDs and separate data toggle sequence bits for the data transmitter and receiver. Only in the receiver can receive data and with the correct data PID received errorfree packet when the receiver sequence bit before switching. But only in the data transmitter to receive a legitimate ACK handshake when the transmitter sequence bit before switching. Data transmitter and receiver must be synchronized in the transaction the beginning of the timing of their position. Synchronization mechanism used varies with the transaction type. ISO does not support data transmission switch synchronization. Control transfers use the SETUP token for initializing host and function sequence bits. Figure 844 shows the host issuing a SETUP packet to a function followed by an OUT transaction. The numbers in the circles represent the transmitter and receiver sequence bits. The function must accept the data and return ACK. When the function accepts the transaction, it must set its sequence bit so that both the host?s and function?s sequence bits are equal to one at the end of the SETUP transaction. If data cannot be accepted or the received data packet is corrupted, the receiver will issue a NAK or STALL handshake, or timeout, depending on the circumstances, and the receiver will not toggle its sequence bit. Any nonACK handshake or timeout will generate similar retry behavior. The transmitter, having not received an ACK handshake, will not toggle its sequence bit. As a result, a failed data packet transaction leaves the transmitter?s and receiver?s sequence bits synchronized and untoggled. The transaction will then be 12 retried and, if successful, will cause both transmitter and receiver sequence bits to toggle. The transmitter is the last and only agent to know for sure whether a transaction has been successful, due to its receiving an ACK handshake. A lost or corrupted ACK handshake can lead to a temporary loss of synchronization between transmitter and receiver as shown in Figure 847. Here the transmitter issues a valid data packet, which is successfully acquired by the receiver。在解釋，要求和回饋中出現(xiàn)的多重字節(jié)部分會被翻譯成可以進(jìn)行跳躍的小型命令字符串。收到的同步信息可以簡單描述為第 7章所述。包位的定義是以未編碼的數(shù)據(jù)格式 顯示出的 。 圖 85顯示了標(biāo)記包的字段格式。只有主機(jī)能發(fā)出標(biāo)記包。輸出和建立 PID定義了從主機(jī)到功能部件的數(shù)據(jù)事務(wù)。標(biāo)記 和幀開始 (SOF)包是被由 3個字節(jié)的包字段數(shù)據(jù)后面包結(jié)束分割開的。 對于 高速總線 以 每 125μs177。包括集線器的所有高速功能部件和全速功能部件都可收到幀開始包。對幀時間敏感而沒必要追蹤幀數(shù)（例如集線器）的功能部件，僅需對 SOF的 PID譯碼 ；可忽略幀數(shù)和其 CRC。只有支持流量控制的交換類型可以進(jìn)行信息交互?，F(xiàn)在一共有四種交互 信息包和一種特殊的交互信息包 1)ACK表示數(shù)據(jù)包被接收沒有位填充或者在數(shù)據(jù)段的 CRC（循環(huán)冗余碼校驗）存在 錯誤 ，并且 沒有收到正確的數(shù)據(jù) PID。 NAK僅在 功能部件的輸入事務(wù)的數(shù)據(jù)時相返回，或在輸出事務(wù)的握手時相返回。 STALL表示功能部件不能發(fā)送或接收數(shù)據(jù)，或者一個控制管道請求不被支持。第一種情況，是當(dāng)掛起特征與端口有聯(lián)系時所設(shè)置的，稱為 “功能 STALL ”。協(xié)議 STALL和功能 STALL在意義和持續(xù)時間上是不同。端口類型有 4種：批處理，控制，中斷和同步。功能部件端口通過返回數(shù)據(jù)包，或者如果不能返回數(shù)據(jù)包，則返回 NAK或 STALL握手作為應(yīng)答。 數(shù)據(jù)傳輸?shù)目刂浦辽儆袃蓚€步驟： 建立以及現(xiàn)狀報告。構(gòu)建服務(wù)的建立總是與 DATA 0 PID使用相關(guān)的。所有的數(shù)據(jù)階段里的事務(wù)都必須有相同的方向（即所有輸入或者所有輸出）。 在時相態(tài)的傳輸控制是最后一個操作序列。 中斷事務(wù)可以由輸入或輸出 組成 。如果一個中斷正在等待，功能部件返回這個中斷信息像返回一個數(shù)據(jù)包那樣。這個‘保證’功能允許只發(fā)送中斷信息知道此信息被主機(jī)接收而不是持續(xù)的發(fā)送中斷數(shù)據(jù)直到這個功能被關(guān)閉并且 USB系統(tǒng)軟件清除了中斷狀況。 只有在接收器能夠接受數(shù)據(jù)且 PID數(shù)據(jù)為無差錯的數(shù)據(jù)包時，接收器時序位才切換。 控制傳送使用建立標(biāo)記初始化主機(jī)和功能部件的時序位。當(dāng)功能部件接受事務(wù)的時候，