+ * Read bytes from the specified serial port, blocking until complete.
+ *
+ * @warning If your program runs on Unix, defines its own signal handlers, and
+ * needs to abort blocking reads when these are called, then you
+ * should not use this function. It repeats system calls that return
+ * with EINTR. To be able to abort a read from a signal handler, you
+ * should implement your own blocking read 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.
+ *
+ * @param port Pointer to port structure.
+ * @param buf Buffer in which to store the bytes read.
+ * @param count Requested number of bytes to read.
+ * @param timeout Timeout in milliseconds, or zero to wait indefinitely.
+ *
+ * @return The number of bytes read on success, or a negative error code. If
+ * the number of bytes returned is less than that requested, the
+ * timeout was reached before the requested number of bytes was
+ * available. If timeout is zero, the function will always return
+ * either the requested number of bytes or a negative error code.
+ *
+ * @since 0.1.0
+ */
+enum sp_return sp_blocking_read(struct sp_port *port, void *buf, size_t count, unsigned int timeout);
+
+/**
+ * Read bytes from the specified serial port, without blocking.
+ *
+ * @param port Pointer to port structure.
+ * @param buf Buffer in which to store the bytes read.
+ * @param count Maximum number of bytes to read.
+ *
+ * @return The number of bytes read on success, or a negative error code. The
+ * number of bytes returned may be any number from zero to the maximum
+ * that was requested.
+ *
+ * @since 0.1.0
+ */
+enum sp_return sp_nonblocking_read(struct sp_port *port, void *buf, size_t count);
+
+/**
+ * Write bytes to the specified serial port, blocking until complete.
+ *
+ * Note that this function only ensures that the accepted bytes have been
+ * written to the OS; they may be held in driver or hardware buffers and not
+ * yet physically transmitted. To check whether all written bytes have actually
+ * been transmitted, use the sp_output_waiting() function. To wait until all
+ * written bytes have actually been transmitted, use the sp_drain() function.
+ *
+ * @warning If your program runs on Unix, defines its own signal handlers, and
+ * needs to abort blocking writes when these are called, then you
+ * should not use this function. It repeats system calls that return
+ * with EINTR. To be able to abort a write from a signal handler, you
+ * should implement your own blocking write using sp_nonblocking_write()
+ * 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.
+ *
+ * @param port Pointer to port structure.
+ * @param buf Buffer containing the bytes to write.
+ * @param count Requested number of bytes to write.
+ * @param timeout Timeout in milliseconds, or zero to wait indefinitely.
+ *
+ * @return The number of bytes written on success, or a negative error code.
+ * If the number of bytes returned is less than that requested, the
+ * timeout was reached before the requested number of bytes was
+ * written. If timeout is zero, the function will always return
+ * either the requested number of bytes or a negative error code. In
+ * the event of an error there is no way to determine how many bytes
+ * were sent before the error occured.
+ *
+ * @since 0.1.0
+ */
+enum sp_return sp_blocking_write(struct sp_port *port, const void *buf, size_t count, unsigned int timeout);
+
+/**
+ * Write bytes to the specified serial port, without blocking.
+ *
+ * Note that this function only ensures that the accepted bytes have been
+ * written to the OS; they may be held in driver or hardware buffers and not
+ * yet physically transmitted. To check whether all written bytes have actually
+ * been transmitted, use the sp_output_waiting() function. To wait until all
+ * written bytes have actually been transmitted, use the sp_drain() function.
+ *
+ * @param port Pointer to port structure.
+ * @param buf Buffer containing the bytes to write.
+ * @param count Maximum number of bytes to write.
+ *
+ * @return The number of bytes written on success, or a negative error code.
+ * The number of bytes returned may be any number from zero to the
+ * maximum that was requested.
+ *
+ * @since 0.1.0
+ */
+enum sp_return sp_nonblocking_write(struct sp_port *port, const void *buf, size_t count);