AnsweredAssumed Answered

How many USB devices can handle by i.MX6S USB host controller?

Question asked by torus1000 on Jul 22, 2015
Latest reply on Nov 6, 2015 by Karina Valencia Aguilar
Branched to a new discussion

Hi chip experts,


According with USB specification, up to 127 Devices could be connected to a single Host.
However, there are some bandwidth restrictions for interrupt and isochronous transfer types.
If the bandwidth limit is reached, no more Devices with the same requirements could be enumerated.


So I tried to evaluate 7 USB devices which can communicate with one host controller or not.

Please see attached.


  Transfer mode = Interrupt/IN only

         Transfer period = 2ms

         OS = T-kernel RTOS

         Protocol/USB class = original/original

         Data size = 256/512/1024 byte

In case of  256 byte or 512 byte of data packet size, we confirmed it was OK and there were all 7 IN transactions in 1 uFrame.
But in case of 1024 byte,  there were only 5 IN transactions in 1 uFrame. I guess the bandwidth limit is reached and
2 of IN transactions lost. I expected next transactions include missing 2 but I couldn't find them.


Are there any restrictions related to Host controller?

Can anyone explain about above behavior?