Our design with the L137/L138 using USB0 (the high speed connection) requires 5 hubs connected in serial fashion, that is one hub connected to a downstream hub connected to a downstream hub, etc. We tested this on a HP laptop, no problem. Tested on the OMAP-L137 eval board using USB1 (the full speed link) and no problem. When connected to the USB0 port, only three hubs are recognized, the fourth is not recognized. According to the USB spec, 5 hubs deep is the limit, which is what we are seeing on USB1 and other devices we have tested. Is there some switch in the Linux kernel or does USB0 not support this.