1 files changed, 55 insertions, 0 deletions
diff --git a/tools/pad_checksum.py b/tools/pad_checksum.py
new file mode 100755
index 0000000..d301756
--- /dev/null
+++ b/tools/pad_checksum.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+
+import argparse
+import binascii
+import struct
+import sys
+
+
+def any_int(x):
+    try:
+        return int(x, 0)
+    except:
+        raise argparse.ArgumentTypeError("expected an integer, not '{!r}'".format(x))
+
+
+def bitrev(x, width):
+    return int("{:0{w}b}".format(x, w=width)[::-1], 2)
+
+
+parser = argparse.ArgumentParser()
+parser.add_argument("ifile", help="Input file (binary)")
+parser.add_argument("ofile", help="Output file (assembly)")
+parser.add_argument("-p", "--pad", help="Padded size (bytes), including 4-byte checksum, default 256",
+                    type=any_int, default=256)
+parser.add_argument("-s", "--seed", help="Checksum seed value, default 0",
+                    type=any_int, default=0)
+args = parser.parse_args()
+
+try:
+    idata = open(args.ifile, "rb").read()
+except:
+    sys.exit("Could not open input file '{}'".format(args.ifile))
+
+if len(idata) > args.pad - 4:
+    sys.exit("Input file size ({} bytes) too large for final size ({} bytes)".format(len(idata), args.pad))
+
+idata_padded = idata + bytes(args.pad - 4 - len(idata))
+
+# Our bootrom CRC32 is slightly bass-ackward but it's best to work around for now (FIXME)
+# 100% worth it to save two Thumb instructions
+checksum = bitrev(
+    (binascii.crc32(bytes(bitrev(b, 8) for b in idata_padded), args.seed ^ 0xffffffff) ^ 0xffffffff) & 0xffffffff, 32)
+odata = idata_padded + struct.pack("<L", checksum)
+
+try:
+    with open(args.ofile, "w") as ofile:
+        ofile.write("// Padded and checksummed version of: {}\n\n".format(args.ifile))
+        ofile.write(".cpu cortex-m0plus\n")
+        ofile.write(".thumb\n\n")
+        ofile.write(".section .boot2, \"ax\"\n\n")
+        for offs in range(0, len(odata), 16):
+            chunk = odata[offs:min(offs + 16, len(odata))]
+            ofile.write(".byte {}\n".format(", ".join("0x{:02x}".format(b) for b in chunk)))
+except:
+    sys.exit("Could not open output file '{}'".format(args.ofile))