I have been working with an LPC Link-2 configured with JLink firmware (as
distributed by Segger and LPC). This firmware basically turns the very nice
$20 LPC Link-2 board into a JLink adapter. It is clear to me that Segger
had a hand in this firmware and you can find references to it on their
pages as well as on LPC's pages.
This adapter has two other firmwares choices - either the proprietary
RedLink firmware which works only with LPC Xpresso or also the CMSIS-DAP
firmware. Since I had even less luck with the CMSIS-DAP firmware and I am
much more familiar with JTAG than SWD, I decided to try to use JLink
firmware because that should be supported with OpenOCD.
Well, it didn't work. I have found a couple references to OpenOCD not
working with "newer" JLink firmware on this forum, but nothing clear.
At first I thought it was a hardware problem, but I tested the Segger JLink
proprietary executable on the same system and USB port and cable and it
worked fine. Moreover, after OpenOCD attempted to access the LPC Link-2
JLink, the Segger software stopped working.
After a long while with a USB sniffer, I was able to discern the critical
difference between the USB initialization of Segger JLink software vs.
OpenOCD. The problem appears to be that the LPC Link-2 JLink firmware
crashes if the USB "set_configuration" is called more than once.
On my Ubuntu Linux with libusb 1.0, plugging the device into the system
causes the default configurations to be set. Either the kernel or some user
level service like udev is doing this, not the application. The Segger
software does not call "set_configuration", but OpenOCD tries to reset the
device and then explicitly calls "set_configuration" again, which actually
causes it to happen two more times. This crashes the probe. Clearly what
OpenOCD is doing is "right", but the probe firmware is just stupid.
I was able to comment out the USB reset and set_configuration from jlink.c
and everything worked beautifully.
Unfortunately, the firmware is closed-source and is the latest and only
version available.
So here is the problem: I suspect a few people might be interested in
getting the LPC Link-2 working with OpenOCD because it is such a nice and
yet very cheap JTAG probe. CMSIS-DAP is broken (I may work on that next),
and JLink support is broken too but I know the fix. However, I don't
suspect that the fixes I made will apply to *all* types of JLink, and
strongly suspect they won't.
So, what I''d like to do is either:
1. Based on USB ID detect the LPC Link-2 and apply this workaround
or
2. Add some parameter or command to the jlink adapter so that the TCL
config can control this workaround.
or
3. Something almost entirely different that 1 or 2 that I haven't thought of
The problem with this is that I don't know how to do them, and I don't know
what the most acceptable approach would be. I'm leaning toward option 2,
but I am less confident in what would be involved in doing it that way.
So, I could get a few pointers (especially on how to do option 2) and
suggestions on what people might want to see, I could make a proper patch
for this.
Until then, I have my own private build that "works", and you all have a
"hint"...
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