When using the USB host mode, the STM32 has a pin named OTG_FS_SOF that ST gives very little useful information (in both Datasheet and USB tech documents) other than it has something to do with syncing when driving Audio devices.
However, I've seen various designs where no audio application was used but the SOF pin was connected anyway — pull up with 47k under most cases. Why is that? Is it very important to host mode? Must I connect it, or data wouldn't be sent and received properly? What does it do anyway?