avionic design with actual uboot and tooling

submodule of avionic design uboot bootloader and with included tools to
get you started , read readme.md and readme-tk1-loader.md

u-boot/tools/gdb/serial.h

@@ -0,0 +1,18 @@
+/*
+ * (C) Copyright 2000
+ * Murray Jensen <Murray.Jensen@csiro.au>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <termios.h>
+
+#define SERIAL_ERROR	-1	/* General error, see errno for details */
+#define SERIAL_TIMEOUT	-2
+#define SERIAL_EOF	-3
+
+extern speed_t cvtspeed(char *);
+extern int serialopen(char *, speed_t);
+extern int serialreadchar(int, int);
+extern int serialwrite(int, char *, int);
+extern int serialclose(int);