Clarify uart write

will block until data "has been sent to the UART transmit buffer"

Fixes raspberrypi#1481

src/rp2_common/hardware_uart/include/hardware/uart.h

@@ -356,7 +356,7 @@ static inline bool uart_is_readable(uart_inst_t *uart) {
 /*! \brief  Write to the UART for transmission.
  *  \ingroup hardware_uart
  *
- * This function will block until all the data has been sent to the UART
+ * This function will block until all the data has been sent to the UART transmit buffer
  *
  * \param uart UART instance. \ref uart0 or \ref uart1
  * \param src The bytes to send
@@ -393,7 +393,7 @@ static inline void uart_read_blocking(uart_inst_t *uart, uint8_t *dst, size_t le
 /*! \brief  Write single character to UART for transmission.
  *  \ingroup hardware_uart
  *
- * This function will block until the entire character has been sent
+ * This function will block until the entire character has been sent to the UART transmit buffer
  *
  * \param uart UART instance. \ref uart0 or \ref uart1
  * \param c The character  to send
@@ -405,7 +405,7 @@ static inline void uart_putc_raw(uart_inst_t *uart, char c) {
 /*! \brief  Write single character to UART for transmission, with optional CR/LF conversions
  *  \ingroup hardware_uart
  *
- * This function will block until the character has been sent
+ * This function will block until the character has been sent to the UART transmit buffer
  *
  * \param uart UART instance. \ref uart0 or \ref uart1
  * \param c The character  to send
@@ -422,7 +422,7 @@ static inline void uart_putc(uart_inst_t *uart, char c) {
 /*! \brief  Write string to UART for transmission, doing any CR/LF conversions
  *  \ingroup hardware_uart
  *
- * This function will block until the entire string has been sent
+ * This function will block until the entire string has been sent to the UART transmit buffer
  *
  * \param uart UART instance. \ref uart0 or \ref uart1
  * \param s The null terminated string to send