STM32MP257FAI3 - Can USB 2.0 and USB 3.0 operate simultaneously on the USB3DR interface?

[Nilay Patel]

According to the STM32MP257 datasheet:

• "1× USB 2.0/3.0 high-speed/SuperSpeed dual role data with embedded 480 Mbits/s and 5 Gbits/s PHY"
• "1× PCI Express with embedded 5 Gbits/s PHY (PHY shared with USB 3.0 SuperSpeed)"

I would like to clarify:

1. Can the USB3DR peripheral be used as a USB 3.0 SuperSpeed port while simultaneously supporting USB 2.0 High-Speed operation on the same connector?
2. Is the embedded USB 2.0 PHY always available when the USB3DR interface is enabled?
3. When PCIe is not used, can the USB3DR interface provide both the 480 Mbit/s USB 2.0 and 5 Gbit/s USB 3.0 links together as a standard USB 3.x port?
4. Is the PHY sharing limitation only between PCIe and USB 3.0 SuperSpeed, or does it also affect USB 2.0 functionality?

Any clarification on the USB/PCIe PHY sharing architecture would be appreciated.

[Erwan SZYMANSKI]

Hello ​@Nilay Patel ,

1. Yes, depending on the USB device put on the connector and the speed supported (or configured), the path taken will be either the USB2PHY2 (for HS) or the COMBOPHY (for SS). You can see the subsystem overview in the Reference Manual USB subsystem (USBSS) chapter.
2. Yes, the USB2PHY2 is dedicated physically to the USB3DR controller. It cannot be used by another controller. See https://wiki.st.com/stm32mpu/wiki/USB2PHY_internal_peripheral
3. It can be the case if a SuperSpeed HUB is used for example. You can have multiple devices with different speeds connected to the HUB, then the traffic will pass through COMBOPHY but with different speeds according to the device talking.
4. It is only between USB 3.0 SuperSpeed and PCIe. As HS traffic involves the USB2PHY2, it does not concern the COMBOPHY and so PCIe is free to use it.

I hope it answers your questions.

Kind regards,
Erwan.

[PatrickF]

HI ​@Nilay Patel ,
USB3DR is only managing a single USB-C connector, so, as per USB standard, the superspeed or high-speed are of exclusive usage (possible speed is negotiated with the device on the other side of the USB cable).
 
I confirm that high-speed USB3DR is still available when PCIe is wired (example is STM32MP257F-EV1 board) or super-speed or high-speed USB3DR when PCI is not used (example is STM32MP257F-DK board)

AN5489 also give you some information
 

Regards.

[Nilay Patel]

Thanks for your reply. I would like to clarify one more technical point regarding the USB3DR interface.

Our requirement is to use the USB3DR interface for simultaneous operation of USB 2.0 High-Speed and either USB 3.0 SuperSpeed or PCIe (via a Combo-PHY), with each interface being used for a separate application.

The intended architecture is as follows:

• USB 2.0 High-Speed (480 Mbps): The USB 2.0 D+/D− interface would be used for a keyboard like application.

• USB 3.0 SuperSpeed (5 Gbps) or PCIe: The SuperSpeed TX/RX lanes, or the PCIe lanes of the Combo-PHY, would be used for an Ethernet application through an appropriate USB-to-Ethernet or PCIe-to-Ethernet bridge/controller.

In other words, we would like to use the USB3DR interface such that the USB 2.0 path and the USB 3.0 SuperSpeed/PCIe path operate simultaneously but serve two independent functions.

Could you please confirm the following:

1. Does the USB3DR interface/controller support simultaneous USB 2.0 High-Speed and USB 3.0 SuperSpeed operation for two separate applications?

2. If the PHY supports USB 3.0/PCIe Combo-PHY operation, can the USB 2.0 interface be used for the keyboard while the high-speed PHY is configured for PCIe and connected to a PCIe-to-Ethernet bridge?

3. Are there any hardware, PHY, controller, firmware, or USB/PCIe topology limitations for this architecture?

4. Is there a recommended reference design or block diagram showing this type of simultaneous operation?

[PatrickF]

Hi ​@Nilay Patel 
 

USB3DR can only use one interface at a time. As per USB standard, an USB-C port with super-speed capabilities MUST support both USB high-speed AND super-speed.
Anyway, you could use PCIe for an ethernet bridge. But STM32MP257F already provide up to THREE Ethernet ports.
Note that for a keyboard or similar device, you connect it to a host port, so better to use USBH high-speed (with maybe an soldered Hub chip if you want more hosts ports).

Unless you have a very specific requirements for your product, I recommend to look at STM32MP257F-EV1 or STM32MP257F-DK  board and prototyping/derive your custom product from it.

 

Regards.