+/*
+ *
+ * serial_buf: A buffer that holds keyboard characters for the
+ * Sandbox U-boot.
+ *
+ * invariants:
+ * serial_buf_write == serial_buf_read -> empty buffer
+ * (serial_buf_write + 1) % 16 == serial_buf_read -> full buffer
+ */
+static char serial_buf[16];
+static unsigned int serial_buf_write;
+static unsigned int serial_buf_read;
+