Minimal USB-OTG connection for serial downloader

[frankambrosius]

Dear all,

We have developed a i.MX6 Dual Light board where we deliberately left off the USB-OTG. The DP and DN signals are available on test-pads on the board. The other signals (VBUS and ID) are not available. These are left floating.

For various reasons we now want to (temporarily) use the USB OTG.

When we connect only the DP and DN lines to a PC (short wires to a USB connector), nothing happens when we start a fresh board (nand flash empty, no fuses burned, boot-mode = 00) .

The questions:

1) Is it enough to only connect DP and DN?

2) Should a fresh board in boot-mode 00 always end up in the serial downloader?

3) What should we measure on the DP and DN when the serial downloader starts?

Thank you in advance for your help!

Regards,

Frank

[frankambrosius]

Hi Yuri,

Just to be completely sure: the following setup should result in a usable serial downloader?

And: on a virgin board, the BT_FUSE_SEL is always set to 0?

Sorry for asking the same thing twice, but your answers lead me to believe that out setup should give a working serial downloader. In practice, it is not working...so double checking everything now.

Your help is much appreciated!

Best regards,

Frank

[Yuri]

Hello,

  the BT_FUSE_SEL is not factory burned.

As for the issue, please check  if voltage is present on VDD_USB_CAP.
Also, please follow recommendations of Chapter 8 (Avoiding Board Bring-up Problems)

of “Hardware Development Guide for i.MX 6Quad, 6Dual, 6DualLite,

6Solo Families …”

< http://cache.nxp.com/files/32bit/doc/user_guide/IMX6DQ6SDLHDG.pdf >

Regards,

Yuri.

[frankambrosius]

Hi Yuri,

Thank you for your quick reply!

The USB_H1_VBUS is connected, but the USB_OTG_VBUS not.

Should this be enough to work or does the USB_OTG_VBUS need to be connected as well?

From the figure 1 and the datasheet it looks like the LDO_USB can work with either power supply...

Best regards,

Frank

[Yuri]

Hello,

> it looks like the LDO_USB can work with either power supply...

Yes.

Regards,

Yuri.

[Yuri]

Hello,

1.

  VBUS is needed for USB module and should be provided.

Please look at Figure 1 (i.MX 6DualLite power rails) of app note AN4576

http://cache.freescale.com/files/32bit/doc/app_note/AN4576.pdf

The USB ID may be left float in order to use OTG device mode of i.MX6.

2.

  BOOT_MODE[1:0] = 01 for Serial (USB) Downloader.

When using BOOT_MODE[1:0] = 00 (Boot From Fuses) boot ROM enters Serial
Downloader if BT_FUSE_SEL = 0.

3.

  USB signals activity may be detected during USB boot operations.

Have a great day,
Yuri

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