USB connections

[petrn]

I am new to the ESP32-P4 and I have the Waveshare ESP32-P4-ETH board and I want to test it with the ESPKVM. But I am confused about the USB connections.

The P4 seems to have one USB OTG_HS and one USB OTG_FS and another USB Serial/JTAG controller. The ESPKVM seems to be using the OTG in device mode (so it can simulate a K+M and a MSC device). Is it using the OTG_HS or OTG_FS for this? I did not find any mention about this in the ESPKVM documentation. Is this choice of the USB controller hardcoded or is there a way to choose?

On the Waveshare ESP32-P4-ETH board, the OTG_HS seems to available on a MX1.25 connector, and the OTG_FS seems to be available on the interface pins corresponding to either FS_PHY1 (GPIO24 and GPIO25) or FS_PHY2 (GPIO26 and GPIO27). The OTG_FS is by default on FS_PHY2, but it can be apparently changed with a eFuse. So how exactly do I connect the ESP32-P4-ETH to the host to be controlled by ESPKVM and is there a ready made cable usable for that?

[dexif]

Hi. I use this one. mx1.25 p4
https://www.aliexpress.com/item/1005009552937705.html

[petrn]

OK, thanks, does this mean that you are using the OTG_HS on the MX1.25 connector? The Waveshare cable they sell in their bundles with the ESP32-P4-ETH seems to be with a female Type A USB plug, so it would make more sense for the host mode of OTG, the cable you refer to seems better for a device mode. To learn more about USB on the P4, would you please point me to where in your source code do you choose the OTG_FS for your keyboard + mouse device mode?

[dexif]

Yep - OTG_HS, and on the P4-ETH it's the MX1.25 connector (that's the OTG port into the target).
We don't set the port ourselves - on the P4, esp_tinyusb's TINYUSB_DEFAULT_CONFIG picks the high-speed peripheral (TINYUSB_PORT_HIGH_SPEED_0). See components/kvm_hid/usb_hid.c and esp_tinyusb's tinyusb_default_config.h.

[petrn]

OK, now I start to understand it, thanks a lot for your help.

[petrn]

I have one more questions after reading a bit more about the P4 and it's USB. If I understand it correctly, the ESP32-P4-ETH used with ESPKVM is a "Self-Powered USB device" and according to the Espressif documentation here https://docs.espressif.com/projects/esp-iot-solution/en/latest/usb/usb_overview/usb_device_self_power.html there should be GPIO used for the VBUS voltage monitoring. But when I look to the Waveshare schematic for the board, no such connection seems to be available for the MX1.25 connector for the OTG_HS controller. How does ESPKVM handle this? Does this mean that the USB must be connected to the host all the time as it would not be capable to detect it has been removed?

[dexif]

Yeah, you read it right - no VBUS sense on the MX1.25, and we don't use one. We just take esp_tinyusb's defaults (self_powered = false, vbus_monitor_io = -1), so we skip that self-powered VBUS-monitoring setup from the Espressif doc.

We don't watch VBUS at all - attach/detach comes from TinyUSB's tud_mount_cb/tud_umount_cb (mount on SetConfig, umount on the controller's disconnect), and that's what the console's "target attached" light reads (tud_mounted()).

So no, it doesn't need to be plugged in the whole time - it enumerates when the host powers up and comes back fineafter. The only thing you don't get without VBUS sensing is a guaranteed event on a bare cable-yank, but for a KVM that lives on one machine that never really matters.

[petrn]

OK, understood, thank you.