esp8266/uart: Add support for polling uart device.

esp8266/machine_uart.c

@@ -255,8 +255,22 @@ STATIC mp_uint_t pyb_uart_write(mp_obj_t self_in, const void *buf_in, mp_uint_t
 }
 
 STATIC mp_uint_t pyb_uart_ioctl(mp_obj_t self_in, mp_uint_t request, mp_uint_t arg, int *errcode) {
+    pyb_uart_obj_t *self = self_in;
+    mp_uint_t ret;
+    if (request == MP_STREAM_POLL) {
+        mp_uint_t flags = arg;
+        ret = 0;
+        if ((flags & MP_STREAM_POLL_RD) && uart_rx_any(self->uart_id)) {
+            ret |= MP_STREAM_POLL_RD;
+        }
+        if ((flags & MP_STREAM_POLL_WR) && uart_tx_any_room(self->uart_id)) {
+            ret |= MP_STREAM_POLL_WR;
+        }
+    } else {
         *errcode = MP_EINVAL;
-    return MP_STREAM_ERROR;
+        ret = MP_STREAM_ERROR;
+    }
+    return ret;
 }
 
 STATIC const mp_stream_p_t uart_stream_p = {

esp8266/uart.c

@@ -200,6 +200,21 @@ bool uart_rx_wait(uint32_t timeout_us) {
     }
 }
 
+int uart_rx_any(uint8 uart) {
+    if (input_buf.iget != input_buf.iput) {
+        return true; // have at least 1 char ready for reading
+    }
+    return false;
+}
+
+int uart_tx_any_room(uint8 uart) {
+    uint32_t fifo_cnt = READ_PERI_REG(UART_STATUS(uart)) & (UART_TXFIFO_CNT << UART_TXFIFO_CNT_S);
+    if ((fifo_cnt >> UART_TXFIFO_CNT_S & UART_TXFIFO_CNT) >= 126) {
+        return false;
+    }
+    return true;
+}
+
 // Returns char from the input buffer, else -1 if buffer is empty.
 int uart_rx_char(void) {
     return ringbuf_get(&input_buf);

esp8266/uart.h

@@ -99,5 +99,8 @@ void uart_tx_one_char(uint8 uart, uint8 TxChar);
 void uart_flush(uint8 uart);
 void uart_os_config(int uart);
 void uart_setup(uint8 uart);
+// check status of rx/tx
+int uart_rx_any(uint8 uart);
+int uart_tx_any_room(uint8 uart);
 
 #endif // _INCLUDED_UART_H_