Some microcontrollers, for example the common STM32 line, claim USB capabilities along these lines:
USB 2.0 OTG HS, that is, USB 2.0 FS/HS device/host/OTG controller, integrating the transceivers for full-speed operation, and featuring an ULPI for high-speed operation: an external PHY device connected to the device is required.
Does that mean there is one USB controller, connected to a FS PHY and with the capabilities(/pins, ULPI) to connect to a HS PHY (one or the other), or does that mean there's one standalone controller+PHY couple capped at full speed and something else entirely that would manage an external PHY, which would mean double USB capabilities when using an external PHY ?
The wording of that resource makes me believe the former, but datasheet feature summaries have me believe the latter:
- USB 2.0 full-speed device/host/OTG controller with on-chip PHY
- USB 2.0 high-speed/full-speed device/host/OTG controller with dedicated DMA, on-chip full-speed PHY and on-chip Hi-speed PHY or ULPI depending on the part number
This question Connecting two USB DP/DM also leaves me unsure: "The only time the FS port will be used is during dfu where the ulpi won't be working." ?
I'd love a clarification. Hopefully the underlying concepts aren't STM32 specific.