examples/emcute_mqttsn: allow override of EMCUTE_ID

examples/emcute_mqttsn/Makefile

@@ -33,6 +33,11 @@ USEMODULE += ps
 # For testing we also include the ping6 command and some stats
 USEMODULE += gnrc_icmpv6_echo
 
+# Allow for env-var-based override of the nodes name (EMCUTE_ID)
+ifneq (,$(EMCUTE_ID))
+  CFLAGS += -DEMCUTE_ID=\"$(EMCUTE_ID)\"
+endif
+
 # Comment this out to disable code in RIOT that does safety checking
 # which is not needed in a production environment but helps in the
 # development process:

examples/emcute_mqttsn/README.md

@@ -95,3 +95,13 @@ pub hello/world "One more beer, please."
 ```
 
 That's it, happy publishing!
+
+
+## FAQ
+
+### I can't connect multiple RIOT nodes to a broker, what can I do?
+Each node that connects to the broker must have a unique node ID string set. Per
+default, this example sets this statically ID to `getrud`. If you want to
+connect more than one node to the broker, you need to set a custom ID for each
+node during compile time. Simply use the `EMCUTE_ID` environment variable for
+this, e.g. build with `EMCUTE_ID=horst make all`.

examples/emcute_mqttsn/main.c

@@ -28,8 +28,10 @@
 #include "net/emcute.h"
 #include "net/ipv6/addr.h"
 
-#define EMCUTE_PORT         (1883U)
+#ifndef EMCUTE_ID
 #define EMCUTE_ID           ("gertrud")
+#endif
+#define EMCUTE_PORT         (1883U)
 #define EMCUTE_PRIO         (THREAD_PRIORITY_MAIN - 1)
 
 #define NUMOFSUBS           (16U)