Starting to fix AVR32 UARt code:

- Check for error return values and return errors when they happen
- Return error value when invalid parameters are passed
- uart.setup(): return the actual baud rate set.

src/platform/avr32/platform.c

@@ -348,27 +348,42 @@ u32 platform_uart_setup( unsigned id, u32 baud, int databits, int parity, int st
   opts.baudrate = baud;
 
   // Set stopbits
-  if( stopbits == PLATFORM_UART_STOPBITS_1 )
+  switch (stopbits) {
+  case PLATFORM_UART_STOPBITS_1:
     opts.stopbits = USART_1_STOPBIT;
-  else if( stopbits == PLATFORM_UART_STOPBITS_1_5 )
+    break;
+  case PLATFORM_UART_STOPBITS_1_5:
     opts.stopbits = USART_1_5_STOPBITS;
-  else
+    break;
+  case PLATFORM_UART_STOPBITS_2:
     opts.stopbits = USART_2_STOPBITS;
+    break;
+  default:
+    return 0;
+  }
 
   // Set parity
-  if( parity == PLATFORM_UART_PARITY_EVEN )
+  switch (parity) {
+  case PLATFORM_UART_PARITY_EVEN:
     opts.paritytype = USART_EVEN_PARITY;
-  else if( parity == PLATFORM_UART_PARITY_ODD )
+    break;
+  case PLATFORM_UART_PARITY_ODD:
     opts.paritytype = USART_ODD_PARITY;
-  else
+    break;
+  case PLATFORM_UART_PARITY_NONE:
     opts.paritytype = USART_NO_PARITY;
+    break;
+  default:
+    return 0;
+  }
 
   // Set actual interface
   gpio_enable_module(uart_pins + id * 2, 2 );
-  usart_init_rs232( pusart, &opts, REQ_PBA_FREQ );
+  if ( usart_init_rs232( pusart, &opts, REQ_PBA_FREQ ) != USART_SUCCESS )
+    return 0;
 
-  // [TODO] Return actual baud here
-  return baud;
+  // Return actual baud here
+  return usart_get_async_baudrate(pusart, REQ_PBA_FREQ);
 }
 
 void platform_s_uart_send( unsigned id, u8 data )

src/platform/avr32/usart.c

@@ -111,6 +111,60 @@ static int usart_set_async_baudrate(volatile avr32_usart_t *usart, unsigned int
 }
 
 
+/*! \brief Return the actual baud rate set into the USART
+ *
+ * Baud rate calculation:
+ * \f$ Baudrate = \frac{SelectedClock}{Over \times (CD + \frac{FP}{8})} \f$, \e Over being 16 or 8.
+ *
+ * \param usart     Base address of the USART instance.
+ * \param pba_hz    USART module input clock frequency (PBA clock, Hz).
+ *
+ * \retval baudrate The closest integer to the actual baud rate
+ * \retval 0        UART clock is off or there was some error on our part
+ */
+unsigned int usart_get_async_baudrate(volatile avr32_usart_t *usart, unsigned long pba_hz)
+{
+  unsigned int clock;	// Master clock frequency
+  unsigned int over;    // divisor of 8 or 16
+  unsigned int cd;      // clock divider (0-65535)
+  unsigned int fp;      // fractional part of clock divider (0-7)
+  unsigned int divisor; // What the master clock is divided by to get
+                        // the final baud rate
+
+  // Find 
+  switch ((usart->mr & AVR32_USART_MR_USCLKS_MASK) >> AVR32_USART_MR_USCLKS_OFFSET)
+  {
+    case AVR32_USART_MR_USCLKS_MCK:
+      clock = pba_hz;
+      break;
+
+    case AVR32_USART_MR_USCLKS_MCK_DIV:
+      // I can't figure out where the divider is defined.  The datasheet
+      // section 26.7.1 says it is "product dependent, but generally set to 8".
+      // Fortunately, the code above always selects MCK.
+    case AVR32_USART_MR_USCLKS_SCK:
+      // If we have an external clock, we don't know its frequency here.
+    default:
+      return 0;	
+  }
+
+  over = usart->mr & AVR32_USART_MR_OVER_MASK;
+  cd = (usart->brgr & AVR32_USART_BRGR_CD_MASK) >> AVR32_USART_BRGR_CD_OFFSET;
+  fp = (usart->brgr & AVR32_USART_BRGR_FP_MASK) >> AVR32_USART_BRGR_FP_OFFSET;
+
+  // if CD==0, no baud rate is generated.
+  // if CD==1, the clock divider and fractional part are bypassed.
+  if (cd == 0) return 0;   
+  if (cd == 1) fp = 0;
+
+  // Rewriting "divisor = 8 * (2 - over) * (cd + fp/8)" for integer math:
+  divisor = (2 - over) * (8 * cd + fp);
+
+  // Round to the integer that is closest to the actual result
+  return (clock + divisor/2) / divisor;
+}
+
+
 /*! \brief Calculates a clock divider (\e CD) for the USART synchronous master
  *         modes to generate a baud rate as close as possible to the baud rate
  *         set point.

src/platform/avr32/usart.h

@@ -230,6 +230,16 @@ extern void usart_reset(volatile avr32_usart_t *usart);
  */
 extern int usart_init_rs232(volatile avr32_usart_t *usart, const usart_options_t *opt, long pba_hz);
 
+/*! \brief Returns the actual baud rate set into the USART in async mode
+ *
+ * \param usart   Base address of the USART instance.
+ * \param pba_hz  USART module input clock frequency (PBA clock, Hz).
+ *
+ * \retval baudrate             The nearest integer to the actual baud rate
+ * \retval 0                    No baudrate is being generated or some error
+ */
+extern unsigned int usart_get_async_baudrate(volatile avr32_usart_t *usart, unsigned long pba_hz);
+
 /*! \brief Sets up the USART to use the standard RS232 protocol in TX-only mode.
  *
  * Compared to \ref usart_init_rs232, this function allows very high baud rates