boards/nrf52: thingy52 and ruuvitag don't work with openocd

boards/common/nrf52/Makefile.include

@@ -27,6 +27,10 @@ ifeq (jlink,$(PROGRAMMER))
   endif
   include $(RIOTMAKE)/tools/jlink.inc.mk
 else ifeq (openocd,$(PROGRAMMER))
+  ifneq (,$(filter $(BOARD),ruuvitag thingy52))
+    # openocd doesn't fully work with ruuvitag and thingy52
+    $(error Cannot use OpenOCD with $(BOARD) board)
+  endif
   # setup OpenOCD for flashing. Version 0.10 of OpenOCD doesn't contain support
   # for nrf52dk and nrf52840dk boards. To use OpenOCD with these a version
   # build from source (master > 2018, August the 13rd) is required.

boards/common/nrf52/doc.txt

@@ -14,9 +14,11 @@ Example with `hello-world` application:
     make BOARD=<nrf52 board> -C examples/hello-world flash
 ```
 
-OpenOCD can also be used to flash nrf52 boards. For the moment, the latest
-stable version of OpenOCD (0.10) doesn't contain any support for nrf52 but
-versions built against the current development version can be used.
+OpenOCD can also be used to flash nrf52 boards (except thingy52 and ruuvitag
+because they are hardly coupled with JLink segger_rtt stdio).
+For the moment, the latest stable version of OpenOCD (0.10) doesn't contain any
+support for nrf52 but versions built against the current development version
+can be used.
 
 To flash the board with OpenOCD, use the `PROGRAMMER` variable:
 ```