nuttx/arch/arm/src/lm3s/lm3s_lowputc.c

/**************************************************************************
 * arch/arm/src/lm3s/lm3s_lowputc.c
 *
 *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 **************************************************************************/

/**************************************************************************
 * Included Files
 **************************************************************************/

#include <nuttx/config.h>
#include <sys/types.h>

#include "up_internal.h"
#include "up_arch.h"

#include "chip.h"
#include "lm3s_internal.h"

/**************************************************************************
 * Private Definitions
 **************************************************************************/

/* Configuration **********************************************************/

/* Is there a serial console? */

#if defined(CONFIG_UART0_SERIAL_CONSOLE) && !defined(CONFIG_UART0_DISABLE)
#  undef CONFIG_UART1_SERIAL_CONSOLE
#  define HAVE_CONSOLE 1
#elif defined(CONFIG_UART1_SERIAL_CONSOLE) && !defined(CONFIG_UART1_DISABLE)
#  undef CONFIG_UART0_SERIAL_CONSOLE
#  define HAVE_CONSOLE 1
#else
#  undef CONFIG_UART0_SERIAL_CONSOLE
#  undef CONFIG_UART1_SERIAL_CONSOLE
#  undef HAVE_CONSOLE
#endif

/* Select UART parameters for the selected console */

#if defined(CONFIG_UART0_SERIAL_CONSOLE)
#  define LM3S_CONSOLE_BASE     LM3S_UART0_BASE
#  define LM3S_CONSOLE_BAUD     CONFIG_UART0_BAUD
#  define LM3S_CONSOLE_BITS     CONFIG_UART0_BITS
#  define LM3S_CONSOLE_PARITY   CONFIG_UART0_PARITY
#  define LM3S_CONSOLE_2STOP    CONFIG_UART0_2STOP
#elif defined(CONFIG_UART1_SERIAL_CONSOLE)
#  define LM3S_CONSOLE_BASE     LM3S_UART1_BASE
#  define LM3S_CONSOLE_BAUD     CONFIG_UART1_BAUD
#  define LM3S_CONSOLE_BITS     CONFIG_UART1_BITS
#  define LM3S_CONSOLE_PARITY   CONFIG_UART1_PARITY
#  define LM3S_CONSOLE_2STOP    CONFIG_UART1_2STOP
#else
#  error "No CONFIG_UARTn_SERIAL_CONSOLE Setting"
#endif

/* Get LCRH settings */

#if LM3S_CONSOLE_BITS == 5
#  define UART_LCRH_NBITS UART_LCRH_WLEN_5BITS
#elif LM3S_CONSOLE_BITS == 6
#  define UART_LCRH_NBITS UART_LCRH_WLEN_6BITS
#elif LM3S_CONSOLE_BITS == 7
#  define UART_LCRH_NBITS UART_LCRH_WLEN_7BITS
#elif LM3S_CONSOLE_BITS == 8
#  define UART_LCRH_NBITS UART_LCRH_WLEN_8BITS
#else
#  error "Number of bits not supported"
#endif

#if LM3S_CONSOLE_PARITY == 0
#  define UART_LCRH_PARITY (0)
#elif LM3S_CONSOLE_PARITY == 1
#  define UART_LCRH_PARITY UART_LCRH_PEN
#elif LM3S_CONSOLE_PARITY == 2
#  define UART_LCRH_PARITY (UART_LCRH_PEN|UART_LCRH_EPS)
#else
#  error "Invalid parity selection"
#endif

#if LM3S_CONSOLE_2STOP != 0
#  define UART_LCRH_NSTOP UART_LCRH_STP2
#else
#  define UART_LCRH_NSTOP (0)
#endif

#define UART_LCRH_VALUE (UART_LCRH_NBITS|UART_LCRH_PARITY|UART_LCRH_NSTOP|UART_LCRH_FEN)

/* Calculate BAUD rate from the SYS clock:
 *
 * "The baud-rate divisor is a 22-bit number consisting of a 16-bit integer and a 6-bit
 *  fractional part. The number formed by these two values is used by the baud-rate generator
 *  to determine the bit period. Having a fractional baud-rate divider allows the UART to
 *  generate all the standard baud rates.
 *
 * "The 16-bit integer is loaded through the UART Integer Baud-Rate Divisor (UARTIBRD)
 *  register ... and the 6-bit fractional part is loaded with the UART Fractional Baud-Rate
 *  Divisor (UARTFBRD) register... The baud-rate divisor (BRD) has the following relationship
 *  to the system clock (where BRDI is the integer part of the BRD and BRDF is the fractional
 *  part, separated by a decimal place.):
 *
 *    "BRD = BRDI + BRDF = UARTSysClk / (16 * Baud Rate)
 *
 * "where UARTSysClk is the system clock connected to the UART. The 6-bit fractional number
 *  (that is to be loaded into the DIVFRAC bit field in the UARTFBRD register) can be calculated
 *  by taking the fractional part of the baud-rate divisor, multiplying it by 64, and adding 0.5
 *  to account for rounding errors:
 *
 *    "UARTFBRD[DIVFRAC] = integer(BRDF * 64 + 0.5)
 *
 * "The UART generates an internal baud-rate reference clock at 16x the baud-rate (referred
 *  to as Baud16). This reference clock is divided by 16 to generate the transmit clock, and is
 *  used for error detection during receive operations.
 *
 * "Along with the UART Line Control, High Byte (UARTLCRH) register ..., the UARTIBRD and
 *  UARTFBRD registers form an internal 30-bit register. This internal register is only
 *  updated when a write operation to UARTLCRH is performed, so any changes to the baud-rate
 *  divisor must be followed by a write to the UARTLCRH register for the changes to take effect. ..."
 */

#define LM3S_BRDDEN     (16 * LM3S_CONSOLE_BAUD)
#define LM3S_BRDI       (SYSCLK_FREQUENCY / LM3S_BRDDEN)
#define LM3S_REMAINDER  (SYSCLK_FREQUENCY - LM3S_BRDDEN * LM3S_BRDI)
#define LM3S_DIVFRAC    ((LM3S_REMAINDER * 64 + (LM3S_BRDDEN/2)) / LM3S_BRDDEN)

/* For example: LM3S_CONSOLE_BAUD = 115,200, SYSCLK_FREQUENCY = 20,000,000:
 *
 * LM3S_BRDDEN    = (16 * 115,200)                           = 1,843,200
 * LM3S_BRDI      = 20,000,000 / 1,843,200                   = 10
 * LM3S_REMAINDER = 20,000,000 - 1,843,200 * 10              = 1,568,000
 * LM3S_DIVFRAC   = (1,568,000 * 64 + 921,600) / 1,843,200   = 54
 *
 * Which should yied BAUD = 20,000,000 / (16 * (10 + 54/64)) = 115273.8
 */

/**************************************************************************
 * Private Types
 **************************************************************************/

/**************************************************************************
 * Private Function Prototypes
 **************************************************************************/

/**************************************************************************
 * Global Variables
 **************************************************************************/

/**************************************************************************
 * Private Variables
 **************************************************************************/

/**************************************************************************
 * Private Functions
 **************************************************************************/

/**************************************************************************
 * Public Functions
 **************************************************************************/

/**************************************************************************
 * Name: up_lowputc
 *
 * Description:
 *   Output one byte on the serial console
 *
 **************************************************************************/

void up_lowputc(char ch)
{
#ifdef HAVE_CONSOLE
  /* Wait until the TX FIFO is not full */

  while ((getreg32(LM3S_CONSOLE_BASE+LM3S_UART_FR_OFFSET) & UART_FR_TXFF) != 0);

  /* Then send the character */

  putreg32((uint32)ch, LM3S_CONSOLE_BASE+LM3S_UART_DR_OFFSET);
#endif
}

/**************************************************************************
 * Name: up_lowsetup
 *
 * Description:
 *   This performs basic initialization of the UART used for the serial
 *   console.  Its purpose is to get the console output availabe as soon
 *   as possible.
 *
 **************************************************************************/

void up_lowsetup(void)
{
#if defined(HAVE_CONSOLE) && !defined(CONFIG_SUPPRESS_UART_CONFIG)
  uint32 ctl;

  /* Enable the selected console device */
  /* 1. Disable the UART by clearing the UARTEN bit in the UART CTL register */

  ctl = getreg32(LM3S_CONSOLE_BASE+LM3S_UART_CTL_OFFSET);
  ctl &= ~UART_CTL_UARTEN;
  putreg32(ctl, LM3S_CONSOLE_BASE+LM3S_UART_CTL_OFFSET);

  /* 2. Write the integer portion of the BRD to the UART IBRD register */

  putreg32(LM3S_BRDI, LM3S_CONSOLE_BASE+LM3S_UART_IBRD_OFFSET);

  /* 3. Write the fractional portion of the BRD to the UART FBRD register */

  putreg32(LM3S_DIVFRAC, LM3S_CONSOLE_BASE+LM3S_UART_FBRD_OFFSET);

  /* 4. Write the desired serial parameters to the UART LCRH register */

  putreg32(UART_LCRH_VALUE, LM3S_CONSOLE_BASE+LM3S_UART_LCRH_OFFSET);

  /* 5. Enable the UART by setting the UARTEN bit in the UART CTL register */

  ctl |= (UART_CTL_UARTEN|UART_CTL_TXE|UART_CTL_RXE);
  putreg32(ctl, LM3S_CONSOLE_BASE+LM3S_UART_CTL_OFFSET);
#endif

  /* Then configure GPIO pins to enable the selected UARTs.  NOTE: The
   * serial driver later depends on this pin configuration.
   */

#ifndef CONFIG_UART0_DISABLE
  lm3s_configgpio(GPIO_UART0_RX);
  lm3s_configgpio(GPIO_UART0_TX);
#endif

#ifndef CONFIG_UART1_DISABLE
  lm3s_configgpio(GPIO_UART1_RX);
  lm3s_configgpio(GPIO_UART1_TX);
#endif
}