Fix up submodule paths, add some hints for submodule usage

.gitmodules

@@ -1,6 +1,7 @@
 [submodule "lwip/lwip"]
 	path = lwip/lwip
-	url = git://git.savannah.nongnu.org/lwip.git
+	url = git@github.com:SuperHouse/esp-lwip.git
 [submodule "axtls/axtls"]
 	path = axtls/axtls
-	url = ../../axtls-code/
+	url = git@github.com:SuperHouse/axtls.git
+

README.md

@@ -14,10 +14,10 @@ Similar to, but substantially different from, the [Espressif IOT RTOS SDK](https
 
 * The build process uses `GNU Make`, and the utilities `sed` and `grep`. Linux & OS X should have these already. Windows users can get these tools a variety of ways, [MingGW](http://www.mingw.org/wiki/mingw) is one option.
 
-* Use git to clone the esp-open-rtos project:
+* Use git to clone the esp-open-rtos project (note the `--recursive`):
 
 ```
-git clone git@github.com:superhouse/esp-open-rtos.git
+git clone --recursive git@github.com:superhouse/esp-open-rtos.git
 cd esp-open-rtos
 ```
 

axtls/component.mk

@@ -17,3 +17,7 @@ axtls_SRC_DIR = $(AXTLS_DIR)crypto $(AXTLS_DIR)ssl $(ROOT)axtls
 #axtls_CFLAGS = $(CFLAGS) -Wno-address
 
 $(eval $(call component_compile_rules,axtls))
+
+# Helpful error if git submodule not initialised
+$(axtls_SRC_DIR):
+	$(error "axtls git submodule not installed. Please run 'git submodule init' then 'git submodule update'")

common.mk

@@ -149,7 +149,7 @@ $(1)_CFLAGS ?= $(CFLAGS)
 $(1)_CC_ARGS = $(Q) $(CC) $(addprefix -I,$(INC_DIRS)) $$(addprefix -I,$$($(1)_INC_DIR)) $$($(1)_CFLAGS)
 $(1)_AR = $(BUILD_DIR)$(1).a
 
-$$($(1)_OBJ_DIR)%.o: $$($(1)_REAL_ROOT)%.c
+$$($(1)_OBJ_DIR)%.o: $$($(1)_REAL_ROOT)%.c | $$($(1)_SRC_DIR)
 	$(vecho) "CC $$<"
 	$(Q) mkdir -p $$(dir $$@)
 	$$($(1)_CC_ARGS) -c $$< -o $$@

lwip/component.mk

@@ -13,3 +13,7 @@ lwip_CFLAGS = $(CFLAGS) -Wno-address
 
 $(eval $(call component_compile_rules,lwip))
 
+# Helpful error if git submodule not initialised
+$(lwip_SRC_DIR):
+	$(error "LWIP git submodule not installed. Please run 'git submodule init' then 'git submodule update'")
+