OpenOCD nRF52-DK experiments

openocd commit 6b2acc0243f6dd54823c336ded8c20d16cdc50a3
+patch http://openocd.zylin.com/#/c/3215/2

$ ./bootstrap && .configure --prefix=/usr --enable-jlink && make && sudo make install

$ echo -e "source [find \"interface/jlink.cfg\"]\ntransport select swd\nsource [find \"target/nrf52.cfg\"]" > openocd-nrf52dk.cfg

$ openocd -f openocd-nrf52dk.cfg
Open On-Chip Debugger 0.10.0+dev-00093-g6b2acc0 (2017-03-16-16:30)
Licensed under GNU GPL v2
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
adapter speed: 10000 kHz
cortex_m reset_config sysresetreq
Info : No device selected, using first device.
Info : J-Link OB-SAM3U128-V2-NordicSemi compiled Aug 28 2015 19:26:24
Info : Hardware version: 1.00
Info : VTarget = 3.300 V
Info : Reduced speed from 10000 kHz to 1000 kHz (maximum).
Info : Reduced speed from 10000 kHz to 1000 kHz (maximum).
Info : clock speed 10000 kHz
Info : SWD DPIDR 0x2ba01477
Info : nrf52.cpu: hardware has 6 breakpoints, 4 watchpoints
Info : accepting 'gdb' connection on tcp/3333
Warn : Unknown device (HWID 0x000000c7)