c139/c140 jtag anyone?

Christophe Devine devinechristophe at gmail.com
Fri Apr 25 15:36:04 UTC 2014

Hi Craig,

I got JTAG working (thanks to #osmocom!). I first recommend you get a C115
or C118 with JTAG exposed, which is much easier than having to remove the
shields. However remove the plastic cover which makes soldering GND, TDI,
TMS, TDO & TCK easier - be careful not to short them the surrounding
shields! You will see there is actually 8+9 pads, you must disregard the
pin that is left of CTS (it is not shown on
Finally you need a proper VREF. As for me, I just connected the internal
3.3V (TP4) on my Flyswatter2 to the VREF, it appears to work fine (the
Flyswatter1 has a jumper that you can use to bridge VREF and 3.3V).

On Fri, Oct 4, 2013 at 5:08 PM, Craig Comstock <craig_comstock at yahoo.com>wrote:

> I cracked open the shield on my C139 and didn't see the TPs I expected
> from the schematic. I thought maybe the angle of the photo on osmocom hid
> the TPs but it really didn't.
> I'll try my C115 instead since that is more clear and accessible. Flashing
> hello_world on my C115 seemed to fail in a similar fashion as it does on my
> C139 so maybe the same issue exists there.
> I was wrong too... it was TP16 not TP6, so I found TP16 but still haven't
> located TP8 on the C139 schematic.
> -Craig
>   ------------------------------
>  *From:* Craig Comstock <craig_comstock at yahoo.com>
> *To:* "baseband-devel at lists.osmocom.org" <baseband-devel at lists.osmocom.org>
> *Sent:* Thursday, October 3, 2013 9:57 AM
> *Subject:* c139/c140 jtag anyone?
> I'm at the point w/ flashing firmware where I feel like I need to use a
> debugger w/ JTAG. I figured I could probably use serial line logging
> somehow but JTAG seems better and I should learn it anyway.
> Has anyone pried open the shield on a c139/c140 and tried attaching to the
> JTAG test points that are just inside the shield next to the test points
> which are accessible via the battery compartment?
> From what I can gather from the schematics:
> TDI - TP8
> TCK - TP17
> TDO - TP16
> TMS - TP18
> Looking at the board from the battery compartment side with the top of the
> phone pointing North/Up I see at least TP17 is near the right-hand bank of
> test points visible from the battery compartment. From left-to-right there
> I see something like: TP12, TP18?, TP16?, TP17 so it looks like I have two
> of the TPs I need: 17 and 18.
> I can't seem to find TP6 or TP8 anywhere on the schematic.
> -Craig
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