boards/common/qn908x: Compute the image checksum

boards/common/qn908x/Makefile.include

@@ -14,3 +14,17 @@ OPENOCD_CONFIG ?= $(RIOTBOARD)/common/qn908x/dist/openocd.cfg
 # verify the image, which needs to have the WDT disabled but it is normally
 # enabled after a 'reset halt' command.
 OPENOCD_PRE_FLASH_CMDS += "-c qn908x disable_wdog"
+
+# In order to boot, the CPU requires that the Vector table contain a valid
+# checksum in one of the "reserved" fields. We don't generate this checksum when
+# compiling and linking the code, instead this make target computes the checksum
+# in another ELF file and we set it as the FLASHFILE.
+ELFFILE ?= $(BINDIR)/$(APPLICATION).elf
+ELFFILE_CHECKSUM ?= $(ELFFILE:.elf=-checksum.elf)
+
+$(ELFFILE_CHECKSUM): $(ELFFILE)
+	$(Q)$(OBJCOPY) --dump-section .vectors=$<.vectors $<
+	$(Q)$(RIOTBOARD)/common/qn908x/dist/nxp_checksum.py $(if $(Q),--quiet) \
+	  $<.vectors
+	$(Q)$(OBJCOPY) --update-section .vectors=$<.vectors $< $@
+FLASHFILE ?= $(ELFFILE_CHECKSUM)

boards/common/qn908x/dist/nxp_checksum.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2020 iosabi
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+"""
+NXP Vector table checksum generator for RAW binary files.
+
+Computes and verifies the Vector table checksum entry for the NXP QN908x
+family. These MCUs need a specific checksum value in the Vector table in order
+to boot.
+"""
+
+import argparse
+import logging
+import struct
+
+
+class NXPChecksumError(Exception):
+    """Generic tool error."""
+
+
+# Number of uint32_t entries that the checksum covers in the QN908X family.
+# The computed checksum is stored right after these values.
+CHECKSUM_ENTRIES = 7
+
+
+def fix_checksum(binary_name, dry_run):
+    with open(binary_name, 'rb' if dry_run else 'rb+') as fobj:
+
+        checksum_fmt = '<%dI' % (CHECKSUM_ENTRIES + 1)
+        checksum_data_size = struct.calcsize(checksum_fmt)
+        data = fobj.read(checksum_data_size)
+
+        if len(data) < checksum_data_size:
+            raise NXPChecksumError(
+                'File %s is too small, it should have at least %d bytes' % (
+                    binary_name, checksum_data_size))
+
+        values = list(struct.unpack(checksum_fmt, data))
+        checksum = (-sum(values[:-1])) % (1 << 32)
+        if checksum != values[-1]:
+            logging.info(
+                'Computed checksum 0x%.8x doesn\'t match the value in the file '
+                '(0x%.8x), updating...', checksum, values[-1])
+            if not dry_run:
+                fobj.seek(checksum_data_size - 4)
+                fobj.write(struct.pack('<I', checksum))
+            else:
+                logging.info('Checksum not updated [DRY-RUN].')
+            logging.info('Checksum updated. Done.')
+        else:
+            logging.info('Checksum in file is already valid. Done.')
+
+
+def main_func():
+    parser = argparse.ArgumentParser(description=__doc__)
+
+    parser.add_argument('--dry-run', action='store_true', default=False)
+    parser.add_argument('--quiet', action='store_true', default=False)
+    parser.add_argument(
+        'bin', help='Path to RAW binary to check/update', type=str)
+
+    args = parser.parse_args()
+    logging.basicConfig(
+        format='%(filename)s: %(message)s',
+        level=logging.ERROR if args.quiet else logging.INFO)
+
+    fix_checksum(args.bin, args.dry_run)
+
+
+if __name__ == '__main__':
+    main_func()