As best I can tell it's a software limitation. I've found reference to a couple RTOS' around supporting hubs and the stm32f4, although I wasn't really looking for an RTOS, so didn't dig that deeply. I've also found reference to some commercial stacks that support it.
I'm using the ST sample stack, which fundamentally assumes 1 device. So even if I did get USB hub support working, getting the rest of the stack to understand there may be multiple devices would still be an issue. Adding hub support to the sample stack seems beyond the scope of a hobby project, at least for the amount of time I can realistically invest in it. Finding and converting to an RTOS that already supports hubs on this hardware is an option, although my existing adb & pre-adb code would need to be ported.
I'm using the ST sample stack, which fundamentally assumes 1 device. So even if I did get USB hub support working, getting the rest of the stack to understand there may be multiple devices would still be an issue. Adding hub support to the sample stack seems beyond the scope of a hobby project, at least for the amount of time I can realistically invest in it. Finding and converting to an RTOS that already supports hubs on this hardware is an option, although my existing adb & pre-adb code would need to be ported.