+ * Read bytes from the specified serial port, blocking until complete.
+ *
+ * @warning If your program runs on Unix and makes use of signal handlers,
+ * note that this function will repeat blocking system calls that
+ * are interrupted by a signal and return with EINTR. If your program
+ * needs to abort blocking reads when a signal is handled, you will
+ * need to implement your own loop using sp_nonblocking_read()
+ * together with a blocking method that makes sense for your program.
+ * E.g. you can obtain the file descriptor for an open port using
+ * sp_get_port_handle() and use this to call select() or pselect(),
+ * with appropriate arrangements to return if a signal is received.