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?