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TUSB4020BI-Q1: stream control and trasmission delay

user3746678
Intellectual 400 points
Part Number: TUSB4020BI-Q1

Hi,TI engineers,

A question about USB hub TUSB4020BI-Q1 need your help:

Using a USB2.0-Hub to combine two usb data stream into one(maximum rate ：480Mbps ) , USB steam A has a continuous data transmission， say 400Mbps; and USB stream B has periodic data transmission , say 1K Bytes/10ms; how should this two stream occupy the combined USB bus？Time division or something else？ Is there any transmission delay for USB stream B or A？ If yes，how to calculate the time delay？

  • 0
    TI__Guru**** 177241 points

    The hub is transparent and is intended to act as a pass-through.

    The SW in the CPU is responsible for communicating to both device on Stream A and Stream B. The USB communication contains a series of frames. Each frame is 125us, assuming High Speed USB operatio, consists of a Start of Frame (SOF) followed by one or more transactions. Each transaction is made up of a series of packets. A packet is preceded with a sync pattern and ends with an End of Packet (EOP) pattern. At a minimum, a transaction has a token packet. Depending on the transaction, there may be one or more data packets and some transactions may or may not have a handshake packet.

    Thanks

    David

  • 0
    TI__Guru 60870 points

    Please note that USB hub devices are slave devices and simply route packets, the hub doesn't schedule the traffic - this is done by the USB host which is responsible for sending the tokens to the downstream devices.  The devices will not send data until they receive the token from the host.  Also, it should be noted that 400 Mbps throughput would be difficult if not impossible to hit due to the inherent overhead of the USB protocol.

    Regards,

    JMMN