examples/gnrc_border_router: add example for WiFi <-> esp_now BR

This adds an example configuration to use the gnrc_border_router to route
between a regular WiFi network and an esp_now network.

All you need is an esp based board (esp8266, esp32).

Configure the access data for your WiFi network in `Makefile.esp.conf`,
then run

    make BOARD=esp32-wroom-32 USE_ETHOS=0 USE_ESP=1 flash term

to turn a e.g. `esp32-wroom-32` into a boarder router.

You can use other esp based boards as nodes in the network by flashing
e.g. the `gnrc_networking` example.
Be sure to add `CFLAGS += -DGNRC_IPV6_NIB_CONF_SLAAC=1` as otherwise
your esp_now node will not receive a link-local IP address.

examples/gnrc_border_router/Makefile

@@ -7,6 +7,18 @@ BOARD ?= samr21-xpro
 # This has to be the absolute path to the RIOT base directory:
 RIOTBASE ?= $(CURDIR)/../..
 
+# Default to using ethos for providing the uplink when not on native
+UPLINK ?= ethos
+
+# Check if the selected Uplink is valid
+ifeq (,$(filter ethos slip wifi,$(UPLINK)))
+  $(error Supported uplinks are `ethos`, `slip` and `wifi`)
+endif
+
+# Set the SSID and password of your WiFi network here
+WIFI_SSID ?= "Your_WiFi_name"
+WIFI_PASS ?= "Your_secure_password"
+
 # Include packages that pull up and auto-init the link layer.
 # NOTE: 6LoWPAN will be included if IEEE802.15.4 devices are present
 USEMODULE += gnrc_netdev_default
@@ -24,8 +36,12 @@ USEMODULE += ps
 # configure the node as a RPL DODAG root when receiving a prefix.
 #USEMODULE += gnrc_rpl
 
-# Optionally use DHCPv6 instead of UHCP
-USE_DHCPV6 ?= 0
+# When using a WiFi uplink we should use DHCPv6
+ifeq (wifi,$(UPLINK))
+  USE_DHCPV6 ?= 1
+else
+  USE_DHCPV6 ?= 0
+endif
 
 ifeq (1,$(USE_DHCPV6))
   # include DHCPv6 client for 6LoWPAN border router
@@ -35,10 +51,6 @@ else
   USEMODULE += gnrc_uhcpc
 endif
 
-# Optionally use SLIP instead of ethos when not on native
-# (added to USEMODULE in Makefile.board.dep)
-USE_SLIP ?= 0
-
 # Use two network interfaces
 GNRC_NETIF_NUMOF := 2
 
@@ -60,14 +72,17 @@ IPV6_PREFIX ?= 2001:db8::/64
 # communication and stdio over UART, but not on native, as native has a tap
 # interface towards the host.
 ifeq (,$(filter native,$(BOARD)))
-  ifeq (1,$(USE_SLIP))
+  ifeq (slip,$(UPLINK))
     # SLIP baudrate and UART device can be configured from make command
     SLIP_BAUDRATE ?= 115200
     include $(CURDIR)/Makefile.slip.conf
-  else
+  else ifeq (ethos,$(UPLINK))
     # ethos baudrate can be configured from make command
     ETHOS_BAUDRATE ?= 115200
     include $(CURDIR)/Makefile.ethos.conf
+  else ifeq (wifi,$(UPLINK))
+    # SSID and Password need to be configured
+    include $(CURDIR)/Makefile.wifi.conf
   endif
 else
   include $(CURDIR)/Makefile.native.conf

examples/gnrc_border_router/Makefile.board.dep

@@ -1,9 +1,16 @@
 # Put board specific dependencies here
 ifeq (,$(filter native,$(BOARD)))
-  ifeq (1,$(USE_SLIP))
+  ifeq (slip,$(UPLINK))
     USEMODULE += slipdev_stdio
-  else
+  else ifeq (ethos,$(UPLINK))
     USEMODULE += stdio_ethos
+  else ifeq (wifi,$(UPLINK))
+    ifneq (,$(filter esp32 esp8266,$(CPU)))
+      USEMODULE += esp_wifi
+      USEMODULE += esp_now
+    else
+      $(error Only esp32 and esp8266 are currently supported)
+    endif
   endif
 else
   USEMODULE += socket_zep

examples/gnrc_border_router/Makefile.wifi.conf

@@ -0,0 +1,2 @@
+CFLAGS += -DESP_WIFI_SSID=\"$(WIFI_SSID)\"
+CFLAGS += -DESP_WIFI_PASS=\"$(WIFI_PASS)\"