AM335x Mini PCIe USB configuration

Edward McNicholas

Other Parts Discussed in Thread: AM3359

We currently created a AM3359 based board that has 2 mini PCIe slots connected via usb and configured as hosts with the ID pins pulled down. But since the interface is 3.3v power on mini PCIe there was no vbus to feedback to the chip. the problem is that the when the device is plugged in it is not being recognized. In the current PSP 04.06.07.00 is there a way to enable the USB host functionality without a vbus signal? We do have both ports configured as host in the board.c file.

Thanks,

over 12 years ago

0 peaves over 12 years ago

TI__Guru 59585 points

The OTG controller in AM335x expects VBUS to be controlled by the respective DRVVBUS output with a valid VBUS voltage applied to the VBUS input when DRVVBUS is active and no voltage applied to the VBUS input when DRVVBUS is not active.

Regards,
Paul

0 Edward McNicholas over 12 years ago in reply to peaves

Prodigy 80 points

I am trying to use this as a host only port without OTG functionality so is there any way to configure the device as host only with no need for the vbus signal? I the case where I am not supplying 5v but 3.3v to the Mini PCIe card port how would i electrically connect the the DRVVBUS and VBUS pins?

0 peaves over 12 years ago in reply to Edward McNicholas

TI__Guru 59585 points

No. The OTG controller has a hard coded state machine that does not allow you to over-ride this requirement.

Regards,
Paul

0 Edward McNicholas over 12 years ago in reply to peaves

Prodigy 80 points

If there is no way to override should i tie VBUS high to 5V or should i place a load switch from it to 5V controlled by the DRVVBUS? or can i tie DRVVBUS to VBUS?

Thanks

0 peaves over 12 years ago in reply to Edward McNicholas

TI__Guru 59585 points

You must use a VBUS switch controlled by the respective DRVVBUS.

The OTG controller will never enter host mode if it detects a valid VBUS voltage applied to its VBUS pin before a session is started. The OTG controller assumes it is already connected to another host if it detects a valid VBUS level when a session is started and it will go into device mode.

Regards,
Paul

0 ed mcnicholas over 12 years ago in reply to peaves

Intellectual 290 points

What voltage must be seen by the vbus can it be 3.3v or must it be 5v.

Thanks

0 peaves over 12 years ago in reply to ed mcnicholas

TI__Guru 59585 points

The AM335x device expects to find a valid VBUS voltage as defined in the USB specification. The voltage should be greater than 4.75 volts and less than 5.25 volts.

Regards,
Paul

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AM335x Mini PCIe USB configuration