USB systems define the following four transmission modes:
3) Transmission in batches
Mass transfer is a reliable one-way transmission, but can not guarantee the transmission delay, and as far as possible to use the bandwidth, suitable for a large number of data transmission.
Low-rate USB devices cannot transfer large amounts of data, and the maximum packet length is 512 in high-speed batches and 8,16,32,64 in full-speed batches.
When using a USB bus, mass transfers have lower priority than other types of transfers, and the USBHOST will always prioritize other types of transfers and do bulk transfers when the bus has ample bandwidth.
High-speed batch endpoints must support PING operations to report the status of the endpoint to the host, with NYET indicating a negative response and not ready to accept the next one, and ACK indicating a positive response and ready to accept the next one.
4) Synchronous transmission
Synchronous transmission is real-time, unreliable, and does not provide a retransmission mechanism for errors. In both high speed and full speed cases, the maximum length of synchronous packets is 1024, while in lower packets, the maximum data size of packets is 1023.
In ADDITION TO HIGH-SPEED, HIGH-BANDWIDTH SYNCHRONIZATION TERMINALS, WHICH SUPPORT only ONE TRANSACTION PER MICROFRAME, HIGH-BANDWIDTH, HIGH-BANDWIDTH TERMINALS CAN perform THREE synchronous transactions in a MICROFRAME and transmit 3072 bits of data.
Full speed synchronous transmission cannot account for more than 80% of the frames and synchronous transmission cannot account for more than 90% of the microframe time.
Like interrupt endpoints, access to synchronous endpoints has a limited time limit.
There is a discrete transmission between the host controller and the USB HUB that only takes place between the host controller and the HUB, enabling the full/low speed device to connect to the high speed host. Isolation transfer is transparent and invisible to the USB device.
Now the four transmission modes of Wushuang cable have been described. Have you learned it?
