boards: provide stdio_rtt as default module where required

For the moment, hamilton, ruuvitag and thingy52 use stdio_rtt by default.

boards/hamilton/Makefile.dep

@@ -12,3 +12,6 @@ ifneq (,$(filter saul_default,$(USEMODULE)))
   # ToDo: peripherals to be added in the future
   #USEMODULE += apds9007
 endif
+
+# Use Segger's RTT by default for stdio on this board
+DEFAULT_MODULE += stdio_rtt

boards/hamilton/Makefile.include

@@ -3,10 +3,8 @@ export JLINK_DEVICE := atsamr21e18a
 OBJDUMPFLAGS += --disassemble --source --disassembler-options=force-thumb
 OFLAGS := --gap-fill 0xff
 
-# Configure terminal, hamilton doesn't provide any UART, thus use RTT
-TERMPROG = $(RIOTTOOLS)/jlink/jlink.sh
-TERMFLAGS = term-rtt
-
-USEMODULE += stdio_rtt
+# use JLink Segger RTT by default
+RIOT_TERMINAL ?= jlink
+include $(RIOTMAKE)/tools/serial.inc.mk
 
 include $(RIOTMAKE)/tools/jlink.inc.mk

boards/ruuvitag/Makefile.dep

@@ -4,4 +4,7 @@ ifneq (,$(filter saul_default,$(USEMODULE)))
   USEMODULE += lis2dh12_spi
 endif
 
+# Use Segger's RTT by default for stdio on this board
+DEFAULT_MODULE += stdio_rtt
+
 include $(RIOTBOARD)/common/nrf52/Makefile.dep

boards/ruuvitag/Makefile.include

@@ -1,7 +1,11 @@
-# for this board, we are using Segger's RTT as default terminal interface
-USEMODULE += stdio_rtt
-TERMPROG = $(RIOTTOOLS)/jlink/jlink.sh
-TERMFLAGS = term-rtt
+# HACK: replicate dependency resolution in Makefile.dep, only works
+# if `USEMODULE` or `DEFAULT_MODULE` is set by the command line or in the
+# application Makefile.
+ifeq (,$(filter stdio_%,$(DISABLE_MODULE) $(USEMODULE)))
+  RIOT_TERMINAL ?= jlink
+endif
+
+include $(RIOTMAKE)/tools/serial.inc.mk
 
 # use shared Makefile.include
 include $(RIOTBOARD)/common/nrf52xxxdk/Makefile.include

boards/thingy52/Makefile.dep

@@ -4,4 +4,7 @@ ifneq (,$(filter saul_default,$(USEMODULE)))
   USEMODULE += lps22hb
 endif
 
+# Use Segger's RTT by default for stdio on this board
+DEFAULT_MODULE += stdio_rtt
+
 include $(RIOTBOARD)/common/nrf52/Makefile.dep

boards/thingy52/Makefile.include

@@ -1,7 +1,11 @@
-# for this board, we are using Segger's RTT as default terminal interface
-USEMODULE += stdio_rtt
-TERMPROG = $(RIOTTOOLS)/jlink/jlink.sh
-TERMFLAGS = term-rtt
+# HACK: replicate dependency resolution in Makefile.dep, only works
+# if `USEMODULE` or `DEFAULT_MODULE` is set by the command line or in the
+# application Makefile.
+ifeq (,$(filter stdio_%,$(DISABLE_MODULE) $(USEMODULE)))
+  RIOT_TERMINAL ?= jlink
+endif
+
+include $(RIOTMAKE)/tools/serial.inc.mk
 
 # use shared Makefile.include
 include $(RIOTBOARD)/common/nrf52/Makefile.include

makefiles/tools/serial.inc.mk

@@ -26,4 +26,7 @@ else ifeq ($(RIOT_TERMINAL),miniterm)
   # The RIOT shell will still transmit back a CRLF, but at least with --eol LF
   # we avoid sending two lines on every "enter".
   TERMFLAGS ?= --eol LF "$(PORT)" "$(BAUD)"
+else ifeq ($(RIOT_TERMINAL),jlink)
+  TERMPROG = $(RIOTTOOLS)/jlink/jlink.sh
+  TERMFLAGS = term-rtt
 endif