The TetraHub defaults to single TT because at the time of designing HX2 the 2.0 drivers (from Microsoft) were not able to support multiple TT hubs. In order to change the mode to multiple TT, the host must issue a SetInterface Request to the TetraHub. Note that the TeraHub has an option of 0xD2 Load where an external SPI EEPROM is used to set various fileds of the hub descriptor. You may use an EEPROM to set the hub to default to multiple TT mode on enumeration using this 0xD2 load. When the host determines that the hub can indeed support multiple TT, it will send the hub device a Set-Interface request, when the hub will be set to multiple TT Mode.