waf: pad bootloader to multiple of 32 bytes

this ensures that we can write a whole flash line when updating
bootloader from ROMFS

Tools/ardupilotwaf/embed.py

@@ -12,13 +12,24 @@ import os, sys, tempfile, gzip
 def write_encode(out, s):
     out.write(s.encode())
 
-def embed_file(out, f, idx):
+def embed_file(out, f, idx, embedded_name):
     '''embed one file'''
     try:
         contents = open(f,'rb').read()
     except Exception:
         print("Failed to embed %s" % f)
         return False
+
+    pad = 0
+    if embedded_name.endswith("bootloader.bin"):
+        # round size to a multiple of 32 bytes for bootloader, this ensures
+        # it can be flashed on a STM32H7 chip
+        blen = len(contents)
+        pad = (32 - (blen % 32)) % 32
+        if pad != 0:
+            contents += bytes([0xff]*pad)
+            print("Padded %u bytes for %s" % (pad, embedded_name))
+
     write_encode(out, 'static const uint8_t ap_romfs_%u[] = {' % idx)
 
     # compress it
@@ -45,7 +56,7 @@ def create_embedded_h(filename, files):
 
     for i in range(len(files)):
         (name, filename) = files[i]
-        if not embed_file(out, filename, i):
+        if not embed_file(out, filename, i, name):
             return False
 
     write_encode(out, '''const AP_ROMFS::embedded_file AP_ROMFS::files[] = {\n''')