scripts: imgtool: compression ARM thumb filter

Adds ARM thumb filter to imgtool's LZMA2 compression.

Signed-off-by: Mateusz Michalek <mateusz.michalek@nordicsemi.no>

Author: michalek-no

scripts/imgtool/image.py

@@ -70,6 +70,7 @@
         'ROM_FIXED':             0x0000100,
         'COMPRESSED_LZMA1':      0x0000200,
         'COMPRESSED_LZMA2':      0x0000400,
+        'COMPRESSED_ARM_THUMB':  0x0000800,
 }
 
 TLV_VALUES = {
@@ -533,8 +534,10 @@ def create(self, key, public_key_format, enckey, dependencies=None,
 
         compression_flags = 0x0
         if compression_tlvs is not None:
-            if compression_type == "lzma2":
+            if compression_type in ["lzma2", "lzma2armthumb"]:
                 compression_flags = IMAGE_F['COMPRESSED_LZMA2']
+                if compression_type == "lzma2armthumb":
+                    compression_flags |= IMAGE_F['COMPRESSED_ARM_THUMB']
         # This adds the header to the payload as well
         if encrypt_keylen == 256:
             self.add_header(enckey, protected_tlv_size, compression_flags, 256)

scripts/imgtool/main.py

@@ -363,7 +363,7 @@ def convert(self, value, param, ctx):
               help='When encrypting the image using AES, select a 128 bit or '
                    '256 bit key len.')
 @click.option('--compression', default='disabled',
-              type=click.Choice(['disabled', 'lzma2']),
+              type=click.Choice(['disabled', 'lzma2', 'lzma2armthumb']),
               help='Enable image compression using specified type. '
                    'Will fall back without image compression automatically '
                    'if the compression increases the image size.')
@@ -513,7 +513,7 @@ def sign(key, public_key_format, align, version, pad_sig, header_size,
                custom_tlvs, compression_tlvs, int(encrypt_keylen), clear,
                baked_signature, pub_key, vector_to_sign, user_sha)
 
-    if compression == "lzma2":
+    if compression in ["lzma2", "lzma2armthumb"]:
         compressed_img = image.Image(version=decode_version(version),
                   header_size=header_size, pad_header=pad_header,
                   pad=pad, confirm=confirm, align=int(align),
@@ -527,6 +527,8 @@ def sign(key, public_key_format, align, version, pad_sig, header_size,
                 "dict_size": comp_default_dictsize, "lp": comp_default_lp,
                 "lc": comp_default_lc}
         ]
+        if compression == "lzma2armthumb":
+            compression_filters.insert(0, {"id":lzma.FILTER_ARMTHUMB})
         compressed_data = lzma.compress(img.get_infile_data(),filters=compression_filters,
             format=lzma.FORMAT_RAW)
         uncompressed_size = len(img.get_infile_data())