Author: EddieZ_31 Version: **
Translation - Japanese: USBハブのアイソクロナス帯域幅割り当て - KBA228110 - Community Translated (JA)
Why does the HX3 connected to USB 2.0 port not have enough isochronous bandwidth for my second device?
Understanding HUB Transaction Translation Bandwidth Losses
High speed upstream port handling a low speed downstream device ends up with bandwidth losses. However, this issue will not apply to the (USB SuperSpeed (SS) data path. This higher or lower speed device has a separate dedicated data path (also electrically separated) and this will not interfere with the SS upstream port. So, considering the HUB translation bandwidth losses is not correct for SS transactions.
Understanding from Host Driver Perspective
Interface 0 (Default interface setting: No endpoints with non-zero isochronous bandwidth in the default setting)
Isochronous Endpoint 1: maximum packet size = 0 bytes
Isochronous Endpoint 2: maximum packet size = 0 bytes
Interface 0 Alt setting 1
Isochronous Endpoint 1: maximum packet size = 256 bytes
Isochronous Endpoint 2: maximum packet size = 256 bytes
Interface 0 Alt setting 2
Isochronous Endpoint 1: maximum packet size = 512 bytes
Isochronous Endpoint 2: maximum packet size = 512 bytes
Bandwidth throttle down comes from the Host Client Driver based on system USB stack acceptance. USB Host controller stack plays the major role in isochronous bandwidth management.
ISO bandwidth adjustment is beyond any user control. This is dynamically driven by OS USB software stack (root hub driver + Host Controller Driver).
For more details, visit the Microsoft Website.