usart: Add usart_rx().

usart_rx() is a nonblocking USART receive.  Add it for symmetry with
usart_tx().

2 files changed, 17 insertions, 0 deletions

diff --git a/libmaple/usart.c b/libmaple/usart.c
index 998da17..0bdc37a 100644
--- a/libmaple/usart.c
+++ b/libmaple/usart.c
@@ -192,6 +192,22 @@ uint32 usart_tx(usart_dev *dev, const uint8 *buf, uint32 len) {
 }
 
 /**
+ * @brief Nonblocking USART receive.
+ * @param dev Serial port to receive bytes from
+ * @param buf Buffer to store received bytes into
+ * @param len Maximum number of bytes to store
+ * @return Number of bytes received
+ */
+uint32 usart_rx(usart_dev *dev, uint8 *buf, uint32 len) {
+    uint32 rxed = 0;
+    while (usart_data_available(dev) && rxed < len) {
+        *buf++ = usart_getc(dev);
+        rxed++;
+    }
+    return rxed;
+}
+
+/**
  * @brief Transmit an unsigned integer to the specified serial port in
  *        decimal format.
  *
diff --git a/libmaple/usart.h b/libmaple/usart.h
index e747e65..ed00e16 100644
--- a/libmaple/usart.h
+++ b/libmaple/usart.h
@@ -259,6 +259,7 @@ void usart_enable(usart_dev *dev);
 void usart_disable(usart_dev *dev);
 void usart_foreach(void (*fn)(usart_dev *dev));
 uint32 usart_tx(usart_dev *dev, const uint8 *buf, uint32 len);
+uint32 usart_rx(usart_dev *dev, uint8 *buf, uint32 len);
 void usart_putudec(usart_dev *dev, uint32 val);
 
 /**