+#if defined(SERIAL_UART_RTS_LO) && defined(SERIAL_UART_RTS_HI)
+ // Buffer state
+ // Empty: RBUF_SPACE == RBUF_SIZE(head==tail)
+ // Last 1 space: RBUF_SPACE == 2
+ // Full: RBUF_SPACE == 1(last cell of rbuf be never used.)
+ #define RBUF_SPACE() (rbuf_head < rbuf_tail ? (rbuf_tail - rbuf_head) : (RBUF_SIZE - rbuf_head + rbuf_tail))
+ // allow to send
+ #define rbuf_check_rts_lo() do { if (RBUF_SPACE() > 2) SERIAL_UART_RTS_LO(); } while (0)
+ // prohibit to send
+ #define rbuf_check_rts_hi() do { if (RBUF_SPACE() <= 2) SERIAL_UART_RTS_HI(); } while (0)
+#else
+ #define rbuf_check_rts_lo()
+ #define rbuf_check_rts_hi()
+#endif
+
+