Add mksunxi tool to make flashable image

tools/mksunxi.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+import sys
+import struct
+
+def align(num, alignment):
+    if num % alignment != 0:
+        num += (alignment - num % alignment)
+    return num
+
+
+def process_file(input, output):
+    with open(input, 'rb') as fin:
+        content = bytearray(fin.read())
+
+    align_value = 512
+    padded_length = align(len(content), align_value)
+    # pad file to actual length
+    content += b'\x00' * (padded_length - len(content))
+
+    struct_format = '<L8sLL'
+    (instruction, magic, checksum, length) = struct.unpack_from(struct_format, content)
+
+    if magic != b'eGON.BT0':
+        print("Magic is invalid:", magic)
+        return 2
+
+    checksum = 0x5F0A6C39
+    length = align(length, align_value)
+
+    struct.pack_into(struct_format, content, 0, instruction, magic, checksum, length)
+
+    checksum = 0
+    for i in range(0, length, 4):
+        (n, ) = struct.unpack_from('<L', content, i)
+        checksum += n
+        checksum %= 4294967296
+
+    struct.pack_into(struct_format, content, 0, instruction, magic, checksum, length)
+
+    with open(output, 'wb') as fout:
+        fout.write(content)
+    return 0
+
+if __name__ == "__main__":
+    if len(sys.argv) != 3:
+        print("Usage: mksunxi.py input.bin output.bin")
+        exit(1)
+    exit(process_file(sys.argv[1], sys.argv[2]))