+#if USE_SERIAL_1_SW_FLOW || USE_SERIAL_2_SW_FLOW || USE_SERIAL_3_SW_FLOW
+#define HAS_SERIAL_SW_FLOW 1
+#else
+#define HAS_SERIAL_SW_FLOW 0
+#endif
+
+#if USE_SERIAL_1_FLOW && !USE_SERIAL_1_SW_FLOW || USE_SERIAL_2_FLOW && !USE_SERIAL_2_SW_FLOW || USE_SERIAL_3_FLOW && !USE_SERIAL_3_SW_FLOW
+#define HAS_SERIAL_HW_FLOW 1
+#else
+#define HAS_SERIAL_HW_FLOW 0
+#endif
+
+/* ao_serial_stm.c */
+struct ao_stm_usart {
+ struct ao_fifo rx_fifo;
+ struct ao_fifo tx_fifo;
+ struct stm_usart *reg;
+ uint8_t tx_running;
+ uint8_t draining;
+#if HAS_SERIAL_SW_FLOW
+ /* RTS - 0 if we have FIFO space, 1 if not
+ * CTS - 0 if we can send, 0 if not
+ */
+ struct stm_gpio *gpio_rts;
+ struct stm_gpio *gpio_cts;
+ uint8_t pin_rts;
+ uint8_t pin_cts;
+ uint8_t rts;
+#endif
+};
+
+#if HAS_SERIAL_1
+extern struct ao_stm_usart ao_stm_usart1;
+#endif
+
+#if HAS_SERIAL_2
+extern struct ao_stm_usart ao_stm_usart2;
+#endif
+
+#if HAS_SERIAL_3
+extern struct ao_stm_usart ao_stm_usart3;
+#endif
+