esp32/machine_uart: Return None from UART read if no data is available.

dpgeorge · dpgeorge · commit 34e224a4afba · 2018-03-14T13:18:43.000+11:00
This is instead of returning an empty bytes object, and matches how other
ports handle non-blocking UART read behaviour.
diff --git a/ports/esp32/machine_uart.c b/ports/esp32/machine_uart.c
@@ -297,7 +297,7 @@ STATIC mp_uint_t machine_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t siz
 
     int bytes_read = uart_read_bytes(self->uart_num, buf_in, size, time_to_wait);
 
-    if (bytes_read < 0) {
+    if (bytes_read <= 0) {
         *errcode = MP_EAGAIN;
         return MP_STREAM_ERROR;
     }

Original file line number	Diff line number	Diff line change
`@@ -297,7 +297,7 @@ STATIC mp_uint_t machine_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t siz`
`297`	`297`
`298`	`298`	`int bytes_read = uart_read_bytes(self->uart_num, buf_in, size, time_to_wait);`
`299`	`299`
`300`		`- if (bytes_read < 0) {`
	`300`	`+ if (bytes_read <= 0) {`
`301`	`301`	`*errcode = MP_EAGAIN;`
`302`	`302`	`return MP_STREAM_ERROR;`
`303`	`303`	`}`