If I configure the AM3703 USB OTG port (MUSB) as a full speed device, how can I “attach” it to a PC host?

I am using AM3703 OTG port (MUSB) as a full speed device (no OTG feature, a straight full speed device). The transceiver is TPS65921 using ULPI interface. If I want to  “attach” it to a PC USB host, I suppose pull D+ pin high so that the host can detect it. However, I cannot find the way to make D+ pin high. I looked the SDK uboot USBTTY example. The called udc_connect() is basically empty. Can anyone tell me how to make this happen? Thank you.