Merged in hg42/nuttx/lpc17-disable-FDR-2 (pull request #596)

disable LPC17 FDR when not used (second fix)

if a boot loader sets the fractional divider (FDR) the baud rate in
nuttx will be wrong (multiplied by this fraction).

This also has to be added to lpc17_lowputc.c

Unfortunately the constant used for shifting the bits was wrong in the header file, so it took some time to realize this...

Approved-by: Gregory Nutt <gnutt@nuttx.org>

arch/arm/src/lpc17xx/chip/lpc17_uart.h

@@ -342,7 +342,7 @@
 
 #define UART_FDR_DIVADDVAL_SHIFT     (0)       /* Bits 0-3: Baud-rate generation pre-scaler divisor value */
 #define UART_FDR_DIVADDVAL_MASK      (15 << UART_FDR_DIVADDVAL_SHIFT)
-#define UART_FDR_MULVAL_SHIFT        (3)       /* Bits 4-7 Baud-rate pre-scaler multiplier value */
+#define UART_FDR_MULVAL_SHIFT        (4)       /* Bits 4-7 Baud-rate pre-scaler multiplier value */
 #define UART_FDR_MULVAL_MASK         (15 << UART_FDR_MULVAL_SHIFT)
                                                /* Bits 8-31: Reserved */
 /* TER Transmit Enable Register (all) */

arch/arm/src/lpc17xx/lpc17_lowputc.c

@@ -389,6 +389,13 @@ void lpc17_lowsetup(void)
   putreg32(UART_FCR_FIFOEN | UART_FCR_RXTRIGGER_8,
            CONSOLE_BASE + LPC17_UART_FCR_OFFSET);
 
+  /* Disable FDR (fractional divider),
+   * ignored by baudrate calculation => has to be disabled
+   */
+
+  putreg32((1 << UART_FDR_MULVAL_SHIFT) + (0 << UART_FDR_DIVADDVAL_SHIFT),
+           CONSOLE_BASE + LPC17_UART_FDR_OFFSET);
+
   /* Set up the LCR and set DLAB=1 */
 
   putreg32(CONSOLE_LCR_VALUE | UART_LCR_DLAB,

arch/arm/src/lpc17xx/lpc17_serial.c

@@ -920,8 +920,8 @@ static int up_setup(struct uart_dev_s *dev)
       lcr |= (UART_LCR_PE | UART_LCR_PS_EVEN);
     }
 
-  /* Disable FDR (fractional divider, not used by baudrate settings -> has
-   * to be disabled)
+  /* Disable FDR (fractional divider),
+   * ignored by baudrate calculation => has to be disabled
    */
 
   up_serialout(priv, LPC17_UART_FDR_OFFSET,