add script to compress firmware before ota upload (#1065)

* add script to compress firmware before ota upload

* add examples for OTA flashing/updating Sonoff RF Bridge

- use compress script to save space uploading firmware
- use "board_build.ldscript = eagle.flash.1m64.ld" to free some additional space for OTA flashing.

scripts/compressFirmware.py

@@ -0,0 +1,33 @@
+import gzip
+import shutil
+import os
+Import("env")
+
+
+def compressFirmware(source, target, env):
+    """ Compress firmware using gzip for 'compressed OTA upload' """
+    SOURCE_FILE = env.subst("$BUILD_DIR") + os.sep + env.subst("$PROGNAME") + ".bin"
+    SOURCE_BAK = SOURCE_FILE + '.bak'
+    do_compress = True
+    if os.path.exists(SOURCE_FILE) and os.path.exists(SOURCE_BAK):
+        src_mtime = os.stat(SOURCE_FILE).st_mtime
+        bak_mtime = os.stat(SOURCE_BAK).st_mtime
+        """ Recompress if .bin file is newer than .bak file """
+        do_compress = (src_mtime > bak_mtime)
+
+    if do_compress:
+        print("Compressing firmware for upload...")
+        shutil.move(SOURCE_FILE, SOURCE_BAK)
+        with open(SOURCE_BAK, 'rb') as f_in:
+            with gzip.open(SOURCE_FILE, 'wb', compresslevel = 9) as f_out:
+                shutil.copyfileobj(f_in, f_out)
+        """ Set modification time on compressed file so incremental build works """
+        shutil.copystat(SOURCE_BAK, SOURCE_FILE)
+
+    if os.path.exists(SOURCE_BAK):
+        ORG_FIRMWARE_SIZE = os.stat(SOURCE_BAK).st_size
+        GZ_FIRMWARE_SIZE = os.stat(SOURCE_FILE).st_size
+
+        print("Compression reduced firmware size to {:.0f}% (was {} bytes, now {} bytes)".format((GZ_FIRMWARE_SIZE / ORG_FIRMWARE_SIZE) * 100, ORG_FIRMWARE_SIZE, GZ_FIRMWARE_SIZE))
+
+env.AddPostAction("$BUILD_DIR/firmware.bin", [compressFirmware])