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Last Post 28 Jun 2017 12:59 PM by  Adam Ford
DM3730 Torpedo
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Greg Durant
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26 Jun 2017 02:06 PM

    I've a design with the Torpedo (dm3730) in an embedded (SOM interfaced to a USB/Eth bridge device on custom board) implementation. I'm unable to get the SOM to recognize the USB/Eth bridge device physically (USB data lines) interfaced to the SOM's USB OTG port. Additionally, the USB_ID pin is grounded on the custom card to indicate to the SOM it is to be the host. Can you add any insight into what the problem would be? I've since noticed this specific note in the Torpedo HW Specification section 4.6  "In order to for the port to operate as a host, a proper adapter cable must be used;" I'm curious of the implication of this note given there is no "cabling" in an embedded implementation. Is there a recommended embedded implementation (that accounts for functionality added by the adapter cable)? What are the implications, if any, by this note?

     

     
    Adam Ford
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    27 Jun 2017 07:02 AM
    The note is just referring to a mini-USB to OTG adapter which grounds the necessary port to configure the system to appear as a host instead of a client device when attached to the USB. If you've grounded the ID pin, I would expect the SOM to operate in host mode.

    The OTG port is limited to 100mA, so it is possible that if you're trying to draw more power than it can source, the USB device may fail to enumerate on the USB bus. I would also suggest making sure there is a 4.7uF capacitor on VBUS. We have a desisgn checklist (https://support.logicpd.com/DesktopModules/Bring2mind/DMX/Download.aspx?portalid=0&EntryId=586) and there we have an alternative method described if you need more than 100mA.

    What Operating System are you using?

    adam
    Greg Durant
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    27 Jun 2017 05:37 PM
    The operating system is linux.

    With regard to VBUS, it's not used (the carrier board supplies power to all resident circuits including the SOM) in my embedded implementation although (it appears) the linux driver (for the TPS65950) senses VBUS as part of the OTG host/peripheral detection. Can you recommend a HW (modification) solution or do you recommend modifying the driver? If so, are there pitfalls in this approach?

    Greg
    Greg Durant
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    New Member
    Posts:5


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    27 Jun 2017 05:38 PM

    The operating system is linux.

    With regard to VBUS, it's not used (the carrier board supplies power to all resident circuits including the SOM) in my embedded implementation although (it appears) the linux driver (for the TPS65950) senses VBUS as part of the OTG host/peripheral detection. Can you recommend a HW (modification) solution or do you recommend modifying the driver? If so, are there pitfalls in this approach?

    Greg
    Greg Durant
    New Member
    New Member
    Posts:5


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    28 Jun 2017 11:22 AM
    Issue resolved: although the embedded design does not use VBUS (USB1_VBUS) from the SOM for powering circuits, the TPS65950 (SOM's USB controller)/linux driver monitors/compare VBUS levels as it performs USB OTG plug detection. Adding a capacitive load (0.1uf capacitor from VBUS to GND) onto my carrier enables this process.

    Greg
    Adam Ford
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    28 Jun 2017 12:59 PM
    I am glad you got it working. I have been in meetings all morning, so I apologize for the late delay. I was just getting to reply. Our App note suggests 4.7uF. The 0.1uF might work, but a slightly larger cap might be better.

    Please don't hesitate to ask questions.

    adam
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