lm4f/uart: Implement uart_get_baudrate

lib/lm4f/uart.c

@@ -130,6 +130,25 @@ void uart_set_baudrate(uint32_t uart, uint32_t baud)
 	UART_FBRD(uart) = div % 64;
 }
 
+/**
+ * \brief Get UART baudrate
+ *
+ * @param[in] uart UART block register address base @ref uart_reg_base
+ * @return Baud rate in bits per second (bps)
+ */
+uint32_t uart_get_baudrate(uint32_t uart)
+{
+	/* Are we running off the internal clock or system clock? */
+	const uint32_t clock = UART_CC(uart) == UART_CC_CS_PIOSC ? 16000000U : rcc_get_system_clock_frequency();
+
+	/* Read back divisor parts. Baudrate = clock/16 / (ibrd+fbrd/64). */
+	const uint16_t ibrd = UART_IBRD(uart);
+	const uint16_t fbrd = UART_FBRD(uart);
+	uint32_t div = ibrd * 64U + fbrd;
+	/* Recalculate the actual baudrate. Note that 4 comes from 1/(16/64). */
+	return 4U * clock / div;
+}
+
 /**
  * \brief Set UART databits
  *