Use of USB 2.0 Micro AB connector on USB0 (Recovery)


I am reading the Jetson TX2 OEM Product Design Guide and Figure 15 illustrates how to connect the USB interfaces. Regarding USB0, as this is the recovery port, it is important that we can use this port for normal usage and recovery (the Jetson will behave as a host and a device respectively). I have two questions:

(1) Most importantly, in our design we will not be using USB OTG and will not be using a USB 2.0 Micro AB connector. The USB 2.0 signals brought out of the box will be the standard 4 pins (VBUS, GND, D+ and D-). USB0_OTG_ID will not be going to a connector. Is this acceptable? Will we need to strap USB0_OTG_ID to ground or a certain voltage level for this to work?

(2) If possible, could you give a brief explanation of how using the FORCE_RECOV# pin works? The following is my assumption (please correct me if I’m wrong):
When FORCE_RECOV# is pulled low at power up, the TX2i boots up as a device (not host) for USB port 0. As such, it should not output VBUS voltage. I am guessing that the TX2i pulls USB0_EN_OC# low at this point to disable the USB0 load switch? Is this correct? If this is not correct, and we have to find a way to disable the 5V USB VBUS output, does NVIDIA have a suggestion for accomplishing this?

Best regards,

It would be a violation of USB standards to use a type-A (host) to type-A (host) cable (some extensions work this way, but there is also a conversion at one end to put it back to type-B for that end). No type-A connector (host mode) should ever be set up as device mode.

Technically you could do it with custom cables of some sort, but it would be a really bad idea. The type-C of USB3 is the first cable to be universal without some sort of ID detect pin, but this cable type internally does not get around the “type-A is host and type-B is device” theme…it just adds extra wiring.

Only a type-A provides power, and type-B has the option of being self-powered or of pulling power from the type-A.

Using a type-A to type-A or type-B to type-B scheme should be avoided.

Someone else would need to answer the specific signal/pin questions.

Thanks very much,

However, we are not trying to use USB-OTG. Under normal circumstances, the Jetson will be the host and it will be connected to a device. The only thing that will be different is that we want to use USB0 as a recovery port as well. At this point the Jetson will be a device. In our design, we will not be able to use any standard USB connectors, we will be using ruggedized 38999 connectors. So we will not be able to use A, B or AB connectors at all. I’m trying to figure out if USB-OTG is a Jetson requirement for the recovery mode or if it is managed a different way (via the force recovery pin).

Best regards,

Someone else will need to verify, but I believe using USB0 as a recovery port as well should not be a problem if your device tree is correct.

The OTG detect pin is only used if the normally booted system is going to switch behavior between normal host mode and device mode (and you have indicated you are not using this functionality when booted normally). The device mode in recovery does not depend on the ID detect pin, and in recovery mode the Jetson is always a custom device on that port. Just disconnect any external devices (e.g., no keyboard on the port) when using a non-standard connector for recovery mode.

Thanks again. That’s more or less how I thought it should work. As you say, we have no requirement to dynamically switch between host and device. The force recovery signal is sampled at power-up so I expect the Jetson will find a way to disable the 5V bus power (probably with an enable single) so it can comply with being a device and not a host. Even if it does not disable the power, when we go into recovery mode, we should be able to just wire up the USB 2.0 data pins alone (D+ and D-) to the host PC that will be performing a software update to the Jetson and then we should not have any issues with 2 power supplies feeding each other.

If someone could answer if and how the Jetson disables 5V USB power in recovery mode that would be great. But we probably have a workaround either way.

Thanks again,