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Can USB3DR be used with PCI Express if USB3DR is configured as 2.0 e.g Hi-Speed?

Forum|Forum|3 months ago
November 17, 2025
2 replies
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I know that USB3DR cannot be used with PCI Express if USB3DR is configured as SuperSpeed.

But can USB3DR be used with PCI Express if USB3DR is configured as 2.0 e.g Hi-Speed?

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Best answer by AScha.3

USB3DR and PCI Express (PCIe) Mutual Exclusivity

When considering the use of USB3DR and PCI Express (PCIe) on STM32 devices, the key factor is the configuration of the USB3DR interface and its dependency on the ComboPHY:

USB3DR and PCIe cannot be used simultaneously if USB3DR is configured for SuperSpeed (USB 3.0). This is because both interfaces require the use of the ComboPHY, and the hardware design only allows one to be active at a time. The assignment of the ComboPHY is exclusive and must be defined during the product configuration phase.

USB3DR in USB 2.0 (Hi-Speed) Mode

When USB3DR is configured as USB 2.0 Hi-Speed only, it does not require the ComboPHY. Instead, it uses the USB2PHY, which is separate from the ComboPHY. In this configuration, the ComboPHY remains available and can be assigned to the PCIe controller.
Therefore, USB3DR (in USB 2.0 mode) and PCIe can be used simultaneously on STM32 devices, as long as USB3DR is not configured for SuperSpeed operation.

Device Tree and Peripheral Configuration

The device tree and peripheral configuration must reflect this exclusivity. If USB3DR is set to USB 2.0 only, the PCIe controller can be enabled and mapped to the ComboPHY. If USB3DR is set to SuperSpeed, PCIe must be disabled or not mapped to the ComboPHY.

Summary

Yes, USB3DR can be used with PCI Express if USB3DR is configured as 2.0 (Hi-Speed) only. The mutual exclusivity with PCIe applies only when USB3DR is configured for SuperSpeed (USB 3.0), as both would then require the ComboPHY. In USB 2.0 mode, USB3DR uses the USB2PHY, leaving the ComboPHY available for PCIe.

Super User

USB3DR and PCI Express (PCIe) Mutual Exclusivity

When considering the use of USB3DR and PCI Express (PCIe) on STM32 devices, the key factor is the configuration of the USB3DR interface and its dependency on the ComboPHY:

USB3DR and PCIe cannot be used simultaneously if USB3DR is configured for SuperSpeed (USB 3.0). This is because both interfaces require the use of the ComboPHY, and the hardware design only allows one to be active at a time. The assignment of the ComboPHY is exclusive and must be defined during the product configuration phase.

USB3DR in USB 2.0 (Hi-Speed) Mode

When USB3DR is configured as USB 2.0 Hi-Speed only, it does not require the ComboPHY. Instead, it uses the USB2PHY, which is separate from the ComboPHY. In this configuration, the ComboPHY remains available and can be assigned to the PCIe controller.
Therefore, USB3DR (in USB 2.0 mode) and PCIe can be used simultaneously on STM32 devices, as long as USB3DR is not configured for SuperSpeed operation.

Device Tree and Peripheral Configuration

The device tree and peripheral configuration must reflect this exclusivity. If USB3DR is set to USB 2.0 only, the PCIe controller can be enabled and mapped to the ComboPHY. If USB3DR is set to SuperSpeed, PCIe must be disabled or not mapped to the ComboPHY.

Summary

Yes, USB3DR can be used with PCI Express if USB3DR is configured as 2.0 (Hi-Speed) only. The mutual exclusivity with PCIe applies only when USB3DR is configured for SuperSpeed (USB 3.0), as both would then require the ComboPHY. In USB 2.0 mode, USB3DR uses the USB2PHY, leaving the ComboPHY available for PCIe.

Technical Moderator

that's the case on STM32MP257F-EV1 board.

You will have docs, schematics and DTS ready and working.

Regards.

DMårtAuthor

Graduate II

Yes, but they are using from a USB Hub 2.0.

I'm talking about USB3DR pins when they are configured as 2.0 (whithout a hub).

I have already implemented USB3DR onto my PCI Express Mini slot. Looking forward to test it!