wrote the code for the BBB side
diff --git a/bbb_cape/src/bbb/crc.h b/bbb_cape/src/bbb/crc.h
new file mode 100644
index 0000000..b353efc
--- /dev/null
+++ b/bbb_cape/src/bbb/crc.h
@@ -0,0 +1,14 @@
+#ifndef BBB_CRC_H_
+#define BBB_CRC_H_
+
+#include <stdint.h>
+
+namespace cape {
+
+// Calculates a CRC32 checksum for data. This is definitely the same one as the
+// cape MCU does in hardware which seems to be the same one as Ethernet etc use.
+uint32_t CalculateChecksum(uint8_t *data, size_t length);
+
+} // namespace cape
+
+#endif // BBB_CRC_H_