Dragonboard 410c R173/R174 0 ohm pad location?

I want to use the debug uart on the dragonboard. The manual states to solder R173/R174 0 ohm resistors to route the pind to J15 connector.

However, I can’t find the pad locations. I only have the schematics and the HW manual. There is no layout document. Further there are no labels on the board itself. (Or I don’t know where to find that info).

Please help.


@ljking: is this one for you?

If it helps I have some hi-res photos of the board that you can scribble on if you need to point things out:

DB410C back (hi-res) by Daniel Thompson, on Flickr

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Hi @danielt

Yes, this is one I should be answering.

Hi @behlingc

The Dragonboard 410c Layout drawing is here: https://developer.qualcomm.com/download/db410c/assembly-drawing.pdf The PDF is searchable, but you will need to zoom in to see the resistor.

The Debug UART is available at the 96Boards low-speed connector (pins 11,13), you only need to add the resistors if you are connecting to J15 (lower right corner in the picture above). You will also need to add J15 if you want to use this connection, since it is not populated. Of course J15 is a really small connector so you will need to build a PCB to connect to it.

Full disclosure: I am an employee of Qualcomm Canada, any opinions I have expressed in this or any other post may not reflect the opinions of my employer.

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Great, got it working, thanks!

Thank you, I found the resistors on p.4 section 3C (upper right corner) and got it working by connecting J15 GND, UART1_TX_DBG, UART2_RX_DBG (pinout here https://developer.qualcomm.com/download/db410c/schematic.pdf p.30 section 7C) to FTDI 2332 converter. It is properly mapped to ttyMSM0 console on currently used Linux kernels (4.14).

Hi @behlingc

The way you have made the connections are certainly valid and as you have shown, they work, however for other readers of the forum, there are “easier” ways to do this.

The most “obvious” way is to simply plug in the UART Serial UART Serial - 96Boards mezzanine board and use a micro USB cable to your laptop. The UART Serial mezzanine card has exactly the same circuitry on board as the FTDI adapter that you connected. Of course, if you have your own mezzanine board already plugged onto the DragonBoard 410c, then this may not work for you (some mezzanine boards have a pass-through and you can plug the UART Serial card on top of them).

The second less obvious way, which works if you already have a mezzanine board on top of your DragonBoard is to use the Audio Mezzanine board Audio Mezzanine - 96Boards. The Audio Mezzanine board has the same FTDI circuitry as the UART Serial card, but it also has full pass through of both the low-speed and the high speed connections (you can disable the rest of the circuitry on the board by sliding the switch SW1 the OFF position). Most of the camera mezzanine board manufacturers have used this trick while debugging their designs.

Finally, you can also use the Sensors Mezzanine board Sensors - 96Boards, since this also has the same FTDI circuit on board. The Sensors Mezzanine gives you a lot of interesting features (including an Arduino) but is not stackable like the Audio Mezzanine.

Full disclosure: I am an employee of Qualcomm Canada, any opinions I have expressed in this or any other post may not reflect the opinions of my employer.

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