nuttx/drivers/net/enc28j60.c

/****************************************************************************
 * drivers/net/enc28j60.c
 *
 *   Copyright (C) 2010 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 *
 * References:
 * - ENC28J60 Data Sheet, Stand-Alone Ethernet Controller with SPI Interface,
 *   DS39662C, 2008 Microchip Technology Inc.
 *
 * 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>
#if defined(CONFIG_NET) && defined(CONFIG_NET_ENC28J60)

#include <stdint.h>
#include <stdbool.h>
#include <stdint.h>
#include <time.h>
#include <string.h>
#include <debug.h>
#include <wdog.h>
#include <errno.h>

#include <nuttx/irq.h>
#include <nuttx/arch.h>
#include <nuttx/spi.h>
#include <nuttx/wqueue.h>
#include <nuttx/clock.h>
#include <nuttx/enc28j60.h>

#include <net/uip/uip.h>
#include <net/uip/uip-arp.h>
#include <net/uip/uip-arch.h>

#include "enc28j60.h"

/****************************************************************************
 * Definitions
 ****************************************************************************/

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

/* ENC28J60 Configuration Settings:
 *
 * CONFIG_NET_ENC28J60 - Enabled ENC28J60 support
 * CONFIG_ENC28J60_SPIMODE - Controls the SPI mode
 * CONFIG_ENC28J60_FREQUENCY - Define to use a different bus frequency
 * CONFIG_ENC28J60_NINTERFACES - Specifies the number of physical ENC28J60
 *   devices that will be supported.
 * CONFIG_ENC28J60_STATS - Collect network statistics
 * CONFIG_ENC28J60_HALFDUPPLEX - Default is full duplex
 */

/* The ENC28J60 spec says that is supports SPI mode 0,0 only.  However,
 * somtimes you need to tinker with these things.
 */

#ifndef CONFIG_ENC28J60_SPIMODE
#  define CONFIG_ENC28J60_SPIMODE SPIDEV_MODE2
#endif

/* CONFIG_ENC28J60_NINTERFACES determines the number of physical interfaces
 * that will be supported.
 */

#ifndef CONFIG_ENC28J60_NINTERFACES
#  define CONFIG_ENC28J60_NINTERFACES 1
#endif

/* CONFIG_NET_BUFSIZE must always be defined */

#if !defined(CONFIG_NET_BUFSIZE) && (CONFIG_NET_BUFSIZE <= MAX_FRAMELEN)
#  error "CONFIG_NET_BUFSIZE is not valid for the ENC28J60"
#endif

/* We need to have the work queue to handle SPI interrupts */

#if !defined(CONFIG_SCHED_WORKQUEUE) && !defined(CONFIG_SPI_OWNBUS)
#  error "Worker thread support is required (CONFIG_SCHED_WORKQUEUE)"
#endif

/* CONFIG_ENC28J60_DUMPPACKET will dump the contents of each packet to the console. */

#ifdef CONFIG_ENC28J60_DUMPPACKET
#  define enc_dumppacket(m,a,n) lib_dumpbuffer(m,a,n)
#else
#  define enc_dumppacket(m,a,n)
#endif

/* Timing *******************************************************************/

/* TX poll deley = 1 seconds. CLK_TCK is the number of clock ticks per second */

#define ENC_WDDELAY   (1*CLK_TCK)
#define ENC_POLLHSEC  (1*2)

/* TX timeout = 1 minute */

#define ENC_TXTIMEOUT (60*CLK_TCK)

/* Poll timeout */

#define ENC_POLLTIMEOUT MSEC2TICK(50)

/* Packet Memory ************************************************************/

/* Packet memory layout */

#define ALIGNED_BUFSIZE ((CONFIG_NET_BUFSIZE + 255) & ~255)

#define PKTMEM_TX_START 0x0000           /* Start TX buffer at 0 */
#define PKTMEM_TX_ENDP1 ALIGNED_BUFSIZE  /* Allow TX buffer for one frame + */
#define PKTMEM_RX_START PKTMEM_TX_ENDP1  /* Followed by RX buffer */
#define PKTMEM_RX_END   PKTMEM_END       /* RX buffer goes to the end of SRAM */

/* Misc. Helper Macros ******************************************************/

#define enc_rdgreg(priv,ctrlreg) \
  enc_rdgreg2(priv, ENC_RCR | GETADDR(ctrlreg))
#define enc_wrgreg(priv,ctrlreg,wrdata) \
  enc_wrgreg2(priv, ENC_WCR | GETADDR(ctrlreg), wrdata)
#define enc_bfcgreg(priv,ctrlreg,clrbits) \
  enc_wrgreg2(priv, ENC_BFC | GETADDR(ctrlreg), clrbits)
#define enc_bfsgreg(priv,ctrlreg,setbits) \
  enc_wrgreg2(priv, ENC_BFS | GETADDR(ctrlreg), setbits)

/* This is a helper pointer for accessing the contents of the Ethernet header */

#define BUF ((struct uip_eth_hdr *)priv->dev.d_buf)

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

/* The enc_driver_s encapsulates all state information for a single hardware
 * interface
 */

struct enc_driver_s
{
  /* Device control */

  bool          bifup;        /* true:ifup false:ifdown */
  uint8_t       bank;         /* Currently selected bank */
  uint16_t      nextpkt;      /* Next packet address */
  int           irq;          /* GPIO IRQ configured for the ENC28J60 */

  /* Timing */

  WDOG_ID       txpoll;       /* TX poll timer */
  WDOG_ID       txtimeout;    /* TX timeout timer */

  /* We we don't own the SPI bus, then we cannot do SPI accesses from the
   * interrupt handler.
   */
 
#ifndef CONFIG_SPI_OWNBUS
  struct work_s work;         /* Work queue support */
#endif

  /* This is the contained SPI driver intstance */

  FAR struct spi_dev_s *spi;

  /* This holds the information visible to uIP/NuttX */

  struct uip_driver_s dev;    /* Interface understood by uIP */

  /* Statistics */

#ifdef CONFIG_ENC28J60_STATS
  struct enc_stats_s stats;
#endif
};

/****************************************************************************
 * Private Data
 ****************************************************************************/

static struct enc_driver_s g_enc28j60[CONFIG_ENC28J60_NINTERFACES];

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

/* Low-level SPI helpers */

static inline void enc_configspi(FAR struct spi_dev_s *spi);
#ifdef CONFIG_SPI_OWNBUS
static inline void enc_select(FAR struct spi_dev_s *spi);
static inline void enc_deselect(FAR struct spi_dev_s *spi);
#else
static void enc_select(FAR struct spi_dev_s *spi);
static void enc_deselect(FAR struct spi_dev_s *spi);
#endif

/* SPI control register access */

static uint8_t enc_rdgreg2(FAR struct enc_driver_s *priv, uint8_t cmd);
static void enc_wrgreg2(FAR struct enc_driver_s *priv, uint8_t cmd,
         uint8_t wrdata);
static void enc_setbank(FAR struct enc_driver_s *priv, uint8_t bank);
static uint8_t enc_rdbreg(FAR struct enc_driver_s *priv, uint8_t ctrlreg);
static void enc_wrbreg(FAR struct enc_driver_s *priv, uint8_t ctrlreg,
         uint8_t wrdata);
static int  enc_waitbreg(FAR struct enc_driver_s *priv, uint8_t ctrlreg,
         uint8_t bits, uint8_t value);

/* SPI buffer transfers */

static void enc_rdbuffer(FAR struct enc_driver_s *priv, FAR uint8_t *buffer,
         size_t buflen);
static void enc_wrbuffer(FAR struct enc_driver_s *priv,
         FAR const uint8_t *buffer, size_t buflen);

/* PHY register access */

static uint16_t enc_rdphy(FAR struct enc_driver_s *priv, uint8_t phyaddr);
static void enc_wrphy(FAR struct enc_driver_s *priv, uint8_t phyaddr,
         uint16_t phydata);

/* Common TX logic */

static int  enc_transmit(FAR struct enc_driver_s *priv);
static int  enc_uiptxpoll(struct uip_driver_s *dev);

/* Interrupt handling */

static void enc_linkstatus(FAR struct enc_driver_s *priv);
static void enc_txif(FAR struct enc_driver_s *priv);
static void enc_txerif(FAR struct enc_driver_s *priv);
static void enc_txerif(FAR struct enc_driver_s *priv);
static void enc_rxerif(FAR struct enc_driver_s *priv);
static void enc_rxdispath(FAR struct enc_driver_s *priv);
static void enc_pktif(FAR struct enc_driver_s *priv);
static void enc_worker(FAR void *arg);
static int  enc_interrupt(int irq, FAR void *context);

/* Watchdog timer expirations */

static void enc_polltimer(int argc, uint32_t arg, ...);
static void enc_txtimeout(int argc, uint32_t arg, ...);

/* NuttX callback functions */

static int  enc_ifup(struct uip_driver_s *dev);
static int  enc_ifdown(struct uip_driver_s *dev);
static int  enc_txavail(struct uip_driver_s *dev);
#ifdef CONFIG_NET_IGMP
static int  enc_addmac(struct uip_driver_s *dev, FAR const uint8_t *mac);
static int  enc_rmmac(struct uip_driver_s *dev, FAR const uint8_t *mac);
#endif

/* Initialization */

static void enc_pwrsave(FAR struct enc_driver_s *priv);
static void enc_pwrfull(FAR struct enc_driver_s *priv);
static void enc_setmacaddr(FAR struct enc_driver_s *priv);
static int  enc_reset(FAR struct enc_driver_s *priv);

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

/****************************************************************************
 * Function: enc_configspi
 *
 * Description:
 *   Configure the SPI for use with the ENC28J60
 *
 * Parameters:
 *   spi  - Reference to the SPI driver structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/
 
static inline void enc_configspi(FAR struct spi_dev_s *spi)
{
  /* Configure SPI for the ENC28J60.  But only if we own the SPI bus.
   * Otherwise, don't bother because it might change.
   */

#ifdef CONFIG_SPI_OWNBUS
  SPI_SETMODE(spi, CONFIG_ENC28J60_SPIMODE);
  SPI_SETBITS(spi, 8);
#ifdef CONFIG_ENC28J60_FREQUENCY
  SPI_SETFREQUENCY(spi, CONFIG_ENC28J60_FREQUENCY)
#endif
#endif
}

/****************************************************************************
 * Function: enc_select
 *
 * Description:
 *   Select the SPI, locking and  re-configuring if necessary
 *
 * Parameters:
 *   spi  - Reference to the SPI driver structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

#ifdef CONFIG_SPI_OWNBUS
static inline void enc_select(FAR struct spi_dev_s *spi)
{
  /* We own the SPI bus, so just select the chip */

  SPI_SELECT(spi, SPIDEV_ETHERNET, true);
}
#else
static void enc_select(FAR struct spi_dev_s *spi)
{
  /* Select ENC28J60 chip (locking the SPI bus in case there are multiple
   * devices competing for the SPI bus
   */

  SPI_LOCK(spi, true);
  SPI_SELECT(spi, SPIDEV_ETHERNET, true);

  /* Now make sure that the SPI bus is configured for the ENC28J60 (it
   * might have gotten configured for a different device while unlocked)
   */

  SPI_SETMODE(spi, CONFIG_ENC28J60_SPIMODE);
  SPI_SETBITS(spi, 8);
#ifdef CONFIG_ENC28J60_FREQUENCY
  SPI_SETFREQUENCY(spi, CONFIG_ENC28J60_FREQUENCY);
#endif
}
#endif

/****************************************************************************
 * Function: enc_deselect
 *
 * Description:
 *   De-select the SPI
 *
 * Parameters:
 *   spi  - Reference to the SPI driver structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

#ifdef CONFIG_SPI_OWNBUS
static inline void enc_deselect(FAR struct spi_dev_s *spi)
{
  /* We own the SPI bus, so just de-select the chip */

  SPI_SELECT(spi, SPIDEV_ETHERNET, false);
}
#else
static void enc_deselect(FAR struct spi_dev_s *spi)
{
  /* De-select ENC28J60 chip and relinquish the SPI bus. */

  SPI_SELECT(spi, SPIDEV_ETHERNET, false);
  SPI_LOCK(spi, false);
}
#endif

/****************************************************************************
 * Function: enc_rdgreg2
 *
 * Description:
 *   Read a global register (EIE, EIR, ESTAT, ECON2, or ECON1).  The cmd
 *   include the CMD 'OR'd with the the global address register.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *   cmd   - The full command to received (cmd | address)
 *
 * Returned Value:
 *   The value read from the register
 *
 * Assumptions:
 *
 ****************************************************************************/

static uint8_t enc_rdgreg2(FAR struct enc_driver_s *priv, uint8_t cmd)
{
  FAR struct spi_dev_s *spi;
  uint8_t rddata;

  DEBUGASSERT(priv && priv->spi);
  spi = priv->spi;

  /* Select ENC28J60 chip */

  enc_select(spi);

  /* Send the read command and collect the data.  The sequence requires
   * 16-clocks:  8 to clock out the cmd + 8 to clock in the data.
   */

  (void)SPI_SEND(spi, cmd);  /* Clock out the command */
  rddata = SPI_SEND(spi, 0); /* Clock in the data */

  /* De-select ENC28J60 chip */

  enc_deselect(spi);
  return rddata;
}

/****************************************************************************
 * Function: enc_wrgreg2
 *
 * Description:
 *   Write to a global register (EIE, EIR, ESTAT, ECON2, or ECON1).  The cmd
 *   include the CMD 'OR'd with the the global address register.
 *
 * Parameters:
 *   priv   - Reference to the driver state structure
 *   cmd    - The full command to received (cmd | address)
 *   wrdata - The data to send
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_wrgreg2(FAR struct enc_driver_s *priv, uint8_t cmd,
                        uint8_t wrdata)
{
  FAR struct spi_dev_s *spi;

  DEBUGASSERT(priv && priv->spi);
  spi = priv->spi;

  /* Select ENC28J60 chip */

  enc_select(spi);

  /* Send the write command and data.  The sequence requires 16-clocks:
   * 8 to clock out the cmd + 8 to clock out the data.
   */

  (void)SPI_SEND(spi, cmd);    /* Clock out the command */
  (void)SPI_SEND(spi, wrdata); /* Clock out the data */

  /* De-select ENC28J60 chip. */

  enc_deselect(spi);
}

/****************************************************************************
 * Function: enc_setbank
 *
 * Description:
 *   Set the bank for these next control register access.
 *
 * Assumption:
 *   The caller has exclusive access to the SPI bus
 *
 * Parameters:
 *   priv   - Reference to the driver state structure
 *   bank   - The bank to select (0-3)
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_setbank(FAR struct enc_driver_s *priv, uint8_t bank)
{
  /* Check if the bank setting has changed*/

  if (bank != priv->bank)
    {
      /* Select bank 0 (just so that all of the bits are cleared) */

      enc_bfcgreg(priv, ENC_ECON1, ECON1_BSEL_MASK);

      /* Then OR in bits to get the correct bank */

      if (bank != 0)
        {
          enc_bfsgreg(priv, ENC_ECON1, (bank << ECON1_BSEL_SHIFT));
        }

      /* Then remember the bank setting */

      priv->bank = bank;
    }
}

/****************************************************************************
 * Function: enc_rdbreg
 *
 * Description:
 *   Read from a banked control register using the RCR command.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   ctrlreg - Bit encoded address of banked register to read
 *
 * Returned Value:
 *   The byte read from the banked register
 *
 * Assumptions:
 *
 ****************************************************************************/
 
static uint8_t enc_rdbreg(FAR struct enc_driver_s *priv, uint8_t ctrlreg)
{
  FAR struct spi_dev_s *spi;
  uint8_t rddata;

  DEBUGASSERT(priv && priv->spi);
  spi = priv->spi;

  /* Select ENC28J60 chip */

  enc_select(spi);

  /* Set the bank */

  enc_setbank(priv, GETBANK(ctrlreg));

  /* Send the RCR command and collect the data.  How we collect the data
   * depends on if this is a PHY/CAN or not.  The normal sequence requires
   * 16-clocks:  8 to clock out the cmd and  8 to clock in the data.
   */

  (void)SPI_SEND(spi, ENC_RCR | GETADDR(ctrlreg)); /* Clock out the command */
  if (ISPHYMAC(ctrlreg))
    {
      /* The PHY/MAC sequence requires 24-clocks:  8 to clock out the cmd,
       * 8 dummy bits, and 8 to clock in the PHY/MAC data.
       */

      (void)SPI_SEND(spi,0);                       /* Clock in the dummy byte */
    }
  rddata = SPI_SEND(spi, 0);                       /* Clock in the data */

  /* De-select ENC28J60 chip */

  enc_deselect(spi);
  return rddata;
}

/****************************************************************************
 * Function: enc_wrbreg
 *
 * Description:
 *   Write to a banked control register using the WCR command.  Unlike
 *   reading, this same SPI sequence works for normal, MAC, and PHY
 *   registers.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   ctrlreg - Bit encoded address of banked register to write
 *   wrdata  - The data to send
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/
 
static void enc_wrbreg(FAR struct enc_driver_s *priv, uint8_t ctrlreg,
                       uint8_t wrdata)
{
  FAR struct spi_dev_s *spi;

  DEBUGASSERT(priv && priv->spi);
  spi = priv->spi;

  /* Select ENC28J60 chip */

  enc_select(spi);

  /* Set the bank */

  enc_setbank(priv, GETBANK(ctrlreg));

  /* Send the WCR command and data.  The sequence requires 16-clocks:
   * 8 to clock out the cmd + 8 to clock out the data.
   */

  (void)SPI_SEND(spi, ENC_WCR | GETADDR(ctrlreg)); /* Clock out the command */
  (void)SPI_SEND(spi, wrdata);                     /* Clock out the data */

  /* De-select ENC28J60 chip. */

  enc_deselect(spi);
}

/****************************************************************************
 * Function: enc_waitbreg
 *
 * Description:
 *   Wait until banked register bit(s) take a specific value (or a timeout
 *   occurs).
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   ctrlreg - Bit encoded address of banked register to check
 *   bits    - The bits to check (a mask)
 *   value   - The value of the bits to return (value under mask)
 *
 * Returned Value:
 *   OK on success, negated errno on failure
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_waitbreg(FAR struct enc_driver_s *priv, uint8_t ctrlreg,
                        uint8_t bits, uint8_t value)
{
  uint32_t start = g_system_timer;
  uint32_t elapsed;
  uint8_t  rddata;

  /* Loop until the exit condition is met */

  do
    {
      /* Read the byte from the requested banked register */

      rddata  = enc_rdbreg(priv, ctrlreg);
      elapsed = g_system_timer - start;
    }
  while ((rddata & bits) != value || elapsed > ENC_POLLTIMEOUT);
  return (rddata & bits) == value ? -ETIMEDOUT : OK;
}

/****************************************************************************
 * Function: enc_rdbuffer
 *
 * Description:
 *   Read a buffer of data.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   buffer  - A pointer to the buffer to read into
 *   buflen  - The number of bytes to read
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *   Read pointer is set to the correct address
 *
 ****************************************************************************/

static void enc_rdbuffer(FAR struct enc_driver_s *priv, FAR uint8_t *buffer,
                         size_t buflen)
{
  FAR struct spi_dev_s *spi;

  DEBUGASSERT(priv && priv->spi);
  spi = priv->spi;

  /* Select ENC28J60 chip */

  enc_select(spi);

  /* Send the read buffer memory command (ignoring the response) */

  (void)SPI_SEND(spi, ENC_RBM);
 
  /* Then read the buffer data */

  SPI_RECVBLOCK(spi, buffer, buflen);

  /* De-select ENC28J60 chip. */

  enc_deselect(spi);
}

/****************************************************************************
 * Function: enc_wrbuffer
 *
 * Description:
 *   Write a buffer of data.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   buffer  - A pointer to the buffer to write from
 *   buflen  - The number of bytes to write
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *   Read pointer is set to the correct address
 *
 ****************************************************************************/

static void enc_wrbuffer(FAR struct enc_driver_s *priv,
                         FAR const uint8_t *buffer, size_t buflen)
{
  FAR struct spi_dev_s *spi;

  DEBUGASSERT(priv && priv->spi);
  spi = priv->spi;

  /* Select ENC28J60 chip */

  enc_select(spi);

  /* Send the write buffer memory command (ignoring the response) */

  (void)SPI_SEND(spi, ENC_WBM);
 
  /* Then send the buffer */

  SPI_SNDBLOCK(spi, buffer, buflen);

  /* De-select ENC28J60 chip. */

  enc_deselect(spi);
}

/****************************************************************************
 * Function: enc_rdphy
 *
 * Description:
 *   Read 16-bits of PHY data.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   phyaddr - The PHY register address
 *
 * Returned Value:
 *   16-bit value read from the PHY
 *
 * Assumptions:
 *
 ****************************************************************************/

static uint16_t enc_rdphy(FAR struct enc_driver_s *priv, uint8_t phyaddr)
{
  uint16_t data = 0;

  /* Set the PHY address (and start the PHY read operation) */

  enc_wrbreg(priv, ENC_MIREGADR, phyaddr);
  enc_wrbreg(priv, ENC_MICMD, MICMD_MIIRD);

  /* Wait until the PHY read completes */

  if (enc_waitbreg(priv, ENC_MISTAT, MISTAT_BUSY, 0x00) == OK);
    {
      /* Terminate reading */

      enc_wrbreg(priv, ENC_MICMD, 0x00);

      /* Get the PHY data */

      data  = (uint16_t)enc_rdbreg(priv, ENC_MIRDL);
      data |= (uint16_t)enc_rdbreg(priv, ENC_MIRDH) << 8;
    }
  return data;
}

/****************************************************************************
 * Function: enc_wrphy
 *
 * Description:
 *   write 16-bits of PHY data.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *   phyaddr - The PHY register address
 *   phydata - 16-bit data to write to the PHY
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_wrphy(FAR struct enc_driver_s *priv, uint8_t phyaddr,
                      uint16_t phydata)
{
  /* Set the PHY register address */

  enc_wrbreg(priv, ENC_MIREGADR, phyaddr);

  /* Write the PHY data */

  enc_wrbreg(priv, ENC_MIWRL, phydata);
  enc_wrbreg(priv, ENC_MIWRH, phydata >> 8);

  /* Wait until the PHY write completes */

  enc_waitbreg(priv, ENC_MISTAT, MISTAT_BUSY, 0x00);
}

/****************************************************************************
 * Function: enc_transmit
 *
 * Description:
 *   Start hardware transmission.  Called either from:
 *
 *   -  pkif interrupt when an application responds to the receipt of data
 *      by trying to send something, or
 *   -  From watchdog based polling.
 *
 * Parameters:
 *   priv - Reference to the driver state structure
 *
 * Returned Value:
 *   OK on success; a negated errno on failure
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_transmit(FAR struct enc_driver_s *priv)
{
  uint16_t txend;

  /* Increment statistics */

  nllvdbg("Sending packet, pktlen: %d\n", priv->dev.d_len);
#ifdef CONFIG_ENC28J60_STATS
  priv->stats.txrequests++;
#endif

  /* Verify that the hardware is ready to send another packet.  The driver
   * starts a transmission process by setting ECON1.TXRTS. When the packet is
   * finished transmitting or is aborted due to an error/cancellation, the
   * ECON1.TXRTS bit will be cleared.
   *
   * NOTE: If we got here, then we have committed to sending a packet.
   * higher level logic must have assured that (1) there is no transmission
   * in progress, and that (2) TX-related interrupts are disabled.
   */

  DEBUGASSERT((enc_rdgreg(priv, ENC_ECON1) & ECON1_TXRTS) == 0);
 
  /* Send the packet: address=priv->dev.d_buf, length=priv->dev.d_len */

  enc_dumppacket("Transmit Packet", priv->dev.d_buf, priv->dev.d_len);

  /* Reset the write pointer to start of transmit buffer */

  enc_wrbreg(priv, ENC_EWRPTL, PKTMEM_TX_START & 0xff);
  enc_wrbreg(priv, ENC_EWRPTH, PKTMEM_TX_START >> 8);

  /* Set the TX End pointer based on the size of the packet to send */

  txend = PKTMEM_TX_START +  priv->dev.d_len;
  enc_wrbreg(priv, ENC_ETXNDL, txend & 0xff);
  enc_wrbreg(priv, ENC_ETXNDH, txend >> 8);

  /* Write the per-packet control byte into the transmit buffer */

  enc_wrgreg(priv, ENC_WBM, 0x00);

  /* Copy the packet itself into the transmit buffer */

  enc_wrbuffer(priv, priv->dev.d_buf, priv->dev.d_len);

  /* Set TXRTS to send the packet in the transmit buffer */

  enc_bfsgreg(priv, ENC_ECON1, ECON1_TXRTS);

  /* Setup the TX timeout watchdog (perhaps restarting the timer).  Note:
   * Is there a race condition.  Could the TXIF interrupt occur before
   * the timer is started?
   */

  (void)wd_start(priv->txtimeout, ENC_TXTIMEOUT, enc_txtimeout, 1, (uint32_t)priv);
  return OK;
}

/****************************************************************************
 * Function: enc_uiptxpoll
 *
 * Description:
 *   The transmitter is available, check if uIP has any outgoing packets ready
 *   to send.  This is a callback from uip_poll().  uip_poll() may be called:
 *
 *   1. When the preceding TX packet send is complete,
 *   2. When the preceding TX packet send timesout and the interface is reset
 *   3. During normal TX polling
 *
 * Parameters:
 *   dev  - Reference to the NuttX driver state structure
 *
 * Returned Value:
 *   OK on success; a negated errno on failure
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_uiptxpoll(struct uip_driver_s *dev)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)dev->d_private;

  /* If the polling resulted in data that should be sent out on the network,
   * the field d_len is set to a value > 0.
   */

  nllvdbg("Poll result: d_len=%d\n", priv->dev.d_len);
  if (priv->dev.d_len > 0)
    {
      uip_arp_out(&priv->dev);
      enc_transmit(priv);

      /* Stop the poll now because we can queue only one packet */

      return -EBUSY;
    }

  /* If zero is returned, the polling will continue until all connections have
   * been examined.
   */

  return OK;
}

/****************************************************************************
 * Function: enc_linkstatus
 *
 * Description:
 *   The current link status can be obtained from the PHSTAT1.LLSTAT or
 *   PHSTAT2.LSTAT.
 *
 * Parameters:
 *   priv    - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_linkstatus(FAR struct enc_driver_s *priv)
{
#if 0
  uint16_t regval = enc_rdphy(priv, ENC_PHSTAT2);
  priv->duplex    = ((regval & PHSTAT2_DPXSTAT) != 0);
  priv->carrier   = ((regval & PHSTAT2_LSTAT) != 0);
#endif
}

/****************************************************************************
 * Function: enc_txif
 *
 * Description:
 *   An TXIF interrupt was received indicating that the last TX packet(s) is
 *   done
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_txif(FAR struct enc_driver_s *priv)
{
  /* Update statistics */

#ifdef CONFIG_ENC28J60_STATS
  priv->stats.txifs++;
  if (enc_rdgreg(priv, ENC_ESTAT) & ESTAT_TXABRT)
    {
      priv->stats.txabrts++;
    }
#endif

  /* Clear the request to send bit */

  enc_bfcgreg(priv, ENC_ECON1, ECON1_TXRTS);

  /* If no further xmits are pending, then cancel the TX timeout */

  wd_cancel(priv->txtimeout);

  /* Then poll uIP for new XMIT data */

  (void)uip_poll(&priv->dev, enc_uiptxpoll);
}

/****************************************************************************
 * Function: enc_txerif
 *
 * Description:
 *   An TXERIF interrupt was received indicating that a TX abort has occurred.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_txerif(FAR struct enc_driver_s *priv)
{
  /* Update statistics */

#ifdef CONFIG_ENC28J60_STATS
  priv->stats.txerifs++;
#endif

  /* Reset TX */

  enc_bfsgreg(priv, ENC_ECON1, ECON1_TXRST);
  enc_bfcgreg(priv, ENC_ECON1, ECON1_TXRST | ECON1_TXRTS);

  /* Here we really should re-transmit (I fact, if we want half duplex to
   * work right, then it is necessary to do this!):
   *
   * 1.  Read the TSV:
   *     - Read ETXNDL to get the end pointer
   *     - Read 7 bytes from that pointer + 1 using ENC_RMB.
   * 2. Determine if we need to retransmit.  Check the LATE COLLISION bit, if 
   *    set, then we need to transmit.
   * 3. Retranmit by resetting ECON1_TXRTS.
   */

#ifdef CONFIG_ENC28J60_HALFDUPLEX
#  error "Missing logic for half duplex"
#endif
}

/****************************************************************************
 * Function: enc_rxerif
 *
 * Description:
 *   An RXERIF interrupt was received indicating that the last TX packet(s) is
 *   done
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_rxerif(FAR struct enc_driver_s *priv)
{
  /* Update statistics */

#ifdef CONFIG_ENC28J60_STATS
  priv->stats.rxerifs++;
#endif
}

/****************************************************************************
 * Function: enc_rxdispath
 *
 * Description:
 *   Give the newly received packet to uIP.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_rxdispath(FAR struct enc_driver_s *priv)
{
 /* We only accept IP packets of the configured type and ARP packets */

#ifdef CONFIG_NET_IPv6
  if (BUF->type == HTONS(UIP_ETHTYPE_IP6))
#else
  if (BUF->type == HTONS(UIP_ETHTYPE_IP))
#endif
    {
      nllvdbg("IP packet received (%02x)\n", BUF->type);
      uip_arp_ipin();
      uip_input(&priv->dev);

      /* If the above function invocation resulted in data that should be
       * sent out on the network, the field  d_len will set to a value > 0.
       */

      if (priv->dev.d_len > 0)
        {
          uip_arp_out(&priv->dev);
          enc_transmit(priv);
        }
    }
  else if (BUF->type == htons(UIP_ETHTYPE_ARP))
    {
      nllvdbg("ARP packet received (%02x)\n", BUF->type);
      uip_arp_arpin(&priv->dev);

      /* If the above function invocation resulted in data that should be
       * sent out on the network, the field  d_len will set to a value > 0.
       */

       if (priv->dev.d_len > 0)
         {
           enc_transmit(priv);
         }
     }
  else
    {
      nlldbg("Unsupported packet type dropped (%02x)\n", htons(BUF->type));
    }
}

/****************************************************************************
 * Function: enc_pktif
 *
 * Description:
 *   An interrupt was received indicating the availability of a new RX packet
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_pktif(FAR struct enc_driver_s *priv)
{
  uint8_t  rsv[6];
  uint16_t pktlen;
  uint16_t rxstat;

  /* Update statistics */

#ifdef CONFIG_ENC28J60_STATS
  priv->stats.pktifs++;
#endif

  /* Set the read pointer to the start of the received packet */

  DEBUGASSERT(priv->nextpkt <= PKTMEM_RX_END);
  enc_wrbreg(priv, ENC_ERDPTL, (priv->nextpkt));
  enc_wrbreg(priv, ENC_ERDPTH, (priv->nextpkt) >> 8);

  /* Read the next packet pointer and the 4 byte read status vector (RSV)
   * at the beginning of the received packet
   */

  enc_rdbuffer(priv, rsv, 6);

  /* Decode the new next packet pointer, and the RSV.  The
   * RSV is encoded as:
   *
   *  Bits 0-15:  Indicates length of the received frame. This includes the
   *              destination address, source address, type/length, data,
   *              padding and CRC fields. This field is stored in little-
   *              endian format.
   *  Bits 16-31: Bit encoded RX status.
   */

  priv->nextpkt = (uint16_t)rsv[1] << 8 | (uint16_t)rsv[0];
  pktlen        = (uint16_t)rsv[3] << 8 | (uint16_t)rsv[2];
  rxstat        = (uint16_t)rsv[5] << 8 | (uint16_t)rsv[4];
  nllvdbg("Receiving packet, pktlen: %d\n", pktlen);

  /* Check if the packet was received OK */

  if ((rxstat & RXSTAT_OK) == 0)
    {
      nlldbg("ERROR: RXSTAT: %04x\n", rxstat);
#ifdef CONFIG_ENC28J60_STATS
      priv->stats.rxnotok++;
#endif
    }
 
  /* Check for a usable packet length (4 added for the CRC) */

  else if (pktlen > (CONFIG_NET_BUFSIZE + 4) || pktlen <= (UIP_LLH_LEN + 4))
    {
      nlldbg("Bad packet size dropped (%d)\n", pktlen);
#ifdef CONFIG_ENC28J60_STATS
      priv->stats.rxpktlen++;
#endif	    
    }

  /* Otherwise, read and process the packet */

  else
    {
      /* Save the packet length (without the 4 byte CRC) in priv->dev.d_len*/

      priv->dev.d_len = pktlen - 4;

      /* Copy the data data from the receive buffer to priv->dev.d_buf */

      enc_rdbuffer(priv, priv->dev.d_buf, priv->dev.d_len);
      enc_dumppacket("Received Packet", priv->ld_dev.d_buf, priv->ld_dev.d_len);

      /* Dispatch the packet to uIP */
 
      enc_rxdispath(priv);
    }

  /* Move the RX read pointer to the start of the next received packet.
   * This frees the memory we just read.
   */

  enc_wrbreg(priv, ENC_ERXRDPTL, (priv->nextpkt));
  enc_wrbreg(priv, ENC_ERXRDPTH, (priv->nextpkt) >> 8);

 /* Decrement the packet counter indicate we are done with this packet */

  enc_bfsgreg(priv, ENC_ECON2, ECON2_PKTDEC);
}

/****************************************************************************
 * Function: enc_worker
 *
 * Description:
 *   Perform interrupt handling logic outside of the interrupt handler (on
 *   the work queue thread).
 *
 * Parameters:
 *   arg     - The reference to the driver structure (case to void*)
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_worker(FAR void *arg)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)arg;
  uint8_t eir;

  DEBUGASSERT(priv);

  /* Disable further interrupts by clearing the global interrup enable bit */

  enc_bfcgreg(priv, ENC_EIE, EIE_INTIE);

  /* Loop until all interrupts have been processed (EIR==0).  Note that
   * there is no infinite loop check... if there are always pending interrupts,
   * we are just broken.
   */

  while ((eir = enc_rdgreg(priv, ENC_EIR) & EIR_ALLINTS) != 0)
    {
      /* Handle interrupts according to interrupt register register bit
       * settings
       *
       * DMAIF: The DMA interrupt indicates that the DMA module has completed
       * its memory copy or checksum calculation. Additionally, this interrupt
       * will be caused if the host controller cancels a DMA operation by
       * manually clearing the DMAST bit. Once set, DMAIF can only be cleared
       * by the host controller or by a Reset condition.
       */

      if ((eir & EIR_DMAIF) != 0) /* DMA interrupt */
        {
          /* Not used by this driver. Just clear the interrupt request. */

          enc_bfcgreg(priv, ENC_EIR, EIR_DMAIF);
        }

      /* LINKIF: The LINKIF indicates that the link status has changed.
       * The actual current link status can be obtained from the
       * PHSTAT1.LLSTAT or PHSTAT2.LSTAT. Unlike other interrupt sources, the
       * link status change interrupt is created in the integrated PHY
       * module.
       *
       * To receive it, the host controller must set the PHIE.PLNKIE and
       * PGEIE bits. After setting the two PHY interrupt enable bits, the
       * LINKIF bit will then shadow the contents of the PHIR.PGIF bit.
       *
       * Once LINKIF is set, it can only be cleared by the host controller or
       * by a Reset. The LINKIF bit is read-only. Performing an MII read on
       * the PHIR register will clear the LINKIF, PGIF and PLNKIF bits
       * automatically and allow for future link status change interrupts.
       */

      if ((eir & EIR_LINKIF) != 0) /* Link change interrupt */
        {
          enc_linkstatus(priv);       /* Get current link status */
          enc_rdphy(priv, ENC_PHIR);  /* Clear the LINKIF interrupt */
        }

      /* TXIF: The Transmit Interrupt Flag (TXIF) is used to indicate that
       * the requested packet transmission has ended. Upon transmission
       * completion, abort or transmission cancellation by the host
       * controller, the EIR.TXIF flag will be set to 1.
       *
       * Once TXIF is set, it can only be cleared by the host controller
       * or by a Reset condition. Once processed, the host controller should
       * use the BFC command to clear the EIR.TXIF bit.
       */

      if ((eir & EIR_TXIF) != 0) /* Transmit interrupt */
        {
          enc_txif(priv);                       /* Handle TX completion */
          enc_bfcgreg(priv, ENC_EIR, EIR_TXIF); /* Clear the TXIF interrupt */
        }

      /* TXERIF: The Transmit Error Interrupt Flag (TXERIF) is used to
       * indicate that a transmit abort has occurred. An abort can occur
       * because of any of the following:
       *
       * 1. Excessive collisions occurred as defined by the Retransmission
       *    Maximum (RETMAX) bits in the MACLCON1 register.
       * 2. A late collision occurred as defined by the Collision Window
       *   (COLWIN) bits in the MACLCON2 register.
       * 3. A collision after transmitting 64 bytes occurred (ESTAT.LATECOL
       *    set).
       * 4. The transmission was unable to gain an opportunity to transmit
       *    the packet because the medium was constantly occupied for too long.
       *    The deferral limit (2.4287 ms) was reached and the MACON4.DEFER bit
       *    was clear.
       * 5. An attempt to transmit a packet larger than the maximum frame
       *    length defined by the MAMXFL registers was made without setting
       *    the MACON3.HFRMEN bit or per packet POVERRIDE and PHUGEEN bits.
       *
       * Upon any of these conditions, the EIR.TXERIF flag is set to 1. Once
       * set, it can only be cleared by the host controller or by a Reset
       * condition.
       *
       * After a transmit abort, the TXRTS bit will be cleared, the
       * ESTAT.TXABRT bit will be set and the transmit status vector will be
       * written at ETXND + 1. The MAC will not automatically attempt to
       * retransmit the packet. The host controller may wish to read the
       * transmit status vector and LATECOL bit to determine the cause of
       * the abort. After determining the problem and solution, the host
       * controller should clear the LATECOL (if set) and TXABRT bits so
       * that future aborts can be detected accurately.
       *
       * In Full-Duplex mode, condition 5 is the only one that should cause
       * this interrupt. Collisions and other problems related to sharing
       * the network are not possible on full-duplex networks. The conditions
       * which cause the transmit error interrupt meet the requirements of the
       * transmit interrupt. As a result, when this interrupt occurs, TXIF
       * will also be simultaneously set.
       */

      if ((eir & EIR_TXERIF) != 0) /* Transmit Error Interrupts */
        {
          enc_txerif(priv);                       /* Handle the TX error */
          enc_bfcgreg(priv, ENC_EIR, EIR_TXERIF); /* Clear the TXERIF interrupt */
        }

      /* PKTIF The Receive Packet Pending Interrupt Flag (PKTIF) is used to
       * indicate the presence of one or more data packets in the receive
       * buffer and to provide a notification means for the arrival of new
       * packets. When the receive buffer has at least one packet in it,
       * EIR.PKTIF will be set. In other words, this interrupt flag will be
       * set anytime the Ethernet Packet Count register (EPKTCNT) is non-zero.
       *
       * The PKTIF bit can only be cleared by the host controller or by a Reset
       * condition. In order to clear PKTIF, the EPKTCNT register must be
       * decremented to 0. If the last data packet in the receive buffer is
       * processed, EPKTCNT will become zero and the PKTIF bit will automatically
       * be cleared.
       */

      /* Ignore PKTIF because is unreliable. Use EPKTCNT instead */
      /* if ((eir & EIR_PKTIF) != 0) */
        {
          uint8_t pktcnt = enc_rdbreg(priv, ENC_EPKTCNT);
          if (pktcnt > 0)
            {
#ifdef CONFIG_ENC28J60_STATS
              if (pktcnt > priv->stats.maxpktcnt)
                {
                  priv->stats.maxpktcnt = pktcnt;
                }
#endif
              /* Handle packet receipt */

              enc_pktif(priv);
            }
        }

      /* RXERIF: The Receive Error Interrupt Flag (RXERIF) is used to
       * indicate a receive buffer overflow condition. Alternately, this
       * interrupt may indicate that too many packets are in the receive
       * buffer and more cannot be stored without overflowing the EPKTCNT
       * register.  When a packet is being received and the receive buffer
       * runs completely out of space, or EPKTCNT is 255 and cannot be
       * incremented, the packet being received will be aborted (permanently
       * lost) and the EIR.RXERIF bit will be set to 1.
       *
       * Once set, RXERIF can only be cleared by the host controller or by a
       * Reset condition. Normally, upon the receive error condition, the
       * host controller would process any packets pending from the receive
       * buffer and then make additional room for future packets by
       * advancing the ERXRDPT registers (low byte first) and decrementing
       * the EPKTCNT register.
       *
       * Once processed, the host controller should use the BFC command to
       * clear the EIR.RXERIF bit.
       */

      if ((eir & EIR_RXERIF) != 0) /* Receive Errror Interrupts */
        {
          enc_rxerif(priv);                       /* Handle the RX error */
          enc_bfcgreg(priv, ENC_EIR, EIR_RXERIF); /* Clear the RXERIF interrupt */
        }

    }

  /* Enable Ethernet interrupts */

  enc_bfsgreg(priv, ENC_EIE, EIE_INTIE);
}

/****************************************************************************
 * Function: enc_interrupt
 *
 * Description:
 *   Hardware interrupt handler
 *
 * Parameters:
 *   irq     - Number of the IRQ that generated the interrupt
 *   context - Interrupt register state save info (architecture-specific)
 *
 * Returned Value:
 *   OK on success
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_interrupt(int irq, FAR void *context)
{
  register FAR struct enc_driver_s *priv = &g_enc28j60[0];

  DEBUGASSERT(priv->irq == irq);

#ifdef CONFIG_SPI_OWNBUS
  /* In very simple environments, we own the SPI and can do data transfers
   * from the interrupt handler.  That is actually a very bad idea in any
   * case because it keeps interrupts disabled for a long time.
   */

  enc_worker((FAR void*)priv);
  return OK;
#else
  /* In complex environments, we cannot do SPI transfers from the interrupt
   * handler because semaphores are probably used to lock the SPI bus.  In
   * this case, we will defer processing to the worker thread.  This is also
   * much kinder in the use of system resources and is, therefore, probably
   * a good thing to do in any event.
   */

  return work_queue(&priv->work, enc_worker, (FAR void *)priv, 0);
#endif
}

/****************************************************************************
 * Function: enc_txtimeout
 *
 * Description:
 *   Our TX watchdog timed out.  Called from the timer interrupt handler.
 *   The last TX never completed.  Reset the hardware and start again.
 *
 * Parameters:
 *   argc - The number of available arguments
 *   arg  - The first argument
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_txtimeout(int argc, uint32_t arg, ...)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)arg;
  int ret;

  /* Increment statistics and dump debug info */

  nlldbg("Tx timeout\n");
#ifdef CONFIG_ENC28J60_STATS
  priv->stats.txtimeouts++;
#endif

  /* Then reset the hardware: Take the interface down, then bring it
   * back up
   */
 
  ret = enc_ifdown(&priv->dev);
  DEBUGASSERT(ret == OK);
  ret = enc_ifup(&priv->dev);
  DEBUGASSERT(ret == OK);

  /* Then poll uIP for new XMIT data */

  (void)uip_poll(&priv->dev, enc_uiptxpoll);
}

/****************************************************************************
 * Function: enc_polltimer
 *
 * Description:
 *   Periodic timer handler.  Called from the timer interrupt handler.
 *
 * Parameters:
 *   argc - The number of available arguments
 *   arg  - The first argument
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_polltimer(int argc, uint32_t arg, ...)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)arg;

  /* Verify that the hardware is ready to send another packet.  The driver
   * start a transmission process by setting ECON1.TXRTS. When the packet is
   * finished transmitting or is aborted due to an error/cancellation, the
   * ECON1.TXRTS bit will be cleared.
   */

  if ((enc_rdgreg(priv, ENC_ECON1) & ECON1_TXRTS) == 0)
    {
      /* Yes.. update TCP timing states and poll uIP for new XMIT data. Hmmm..
       * looks like a bug here to me.  Does this mean if there is a transmit
       * in progress, we will missing TCP time state updates?
       */

      (void)uip_timer(&priv->dev, enc_uiptxpoll, ENC_POLLHSEC);
    }

  /* Setup the watchdog poll timer again */

  (void)wd_start(priv->txpoll, ENC_WDDELAY, enc_polltimer, 1, arg);
}

/****************************************************************************
 * Function: enc_ifup
 *
 * Description:
 *   NuttX Callback: Bring up the Ethernet interface when an IP address is
 *   provided 
 *
 * Parameters:
 *   dev  - Reference to the NuttX driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_ifup(struct uip_driver_s *dev)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)dev->d_private;
  int ret;

  nlldbg("Bringing up: %d.%d.%d.%d\n",
         dev->d_ipaddr & 0xff, (dev->d_ipaddr >> 8) & 0xff,
        (dev->d_ipaddr >> 16) & 0xff, dev->d_ipaddr >> 24 );

  /* Initialize Ethernet interface, set the MAC address, and make sure that
   * the ENC28J80 is not in power save mode.
   */

  ret = enc_reset(priv);
  if (ret == OK)
    {
      enc_setmacaddr(priv);
      enc_pwrfull(priv);

      /* Enable interrupts at the ENC28J60.  Interrupts are still disabled
       * at the interrupt controller.
       */

      enc_wrphy(priv, ENC_PHIE, PHIE_PGEIE | PHIE_PLNKIE);
      enc_bfsgreg(priv, ENC_EIE, EIE_INTIE | EIE_PKTIE);
      enc_bfsgreg(priv, ENC_EIR, EIR_DMAIF  | EIR_LINKIF | EIR_TXIF |
                                 EIR_TXERIF | EIR_RXERIF | EIR_PKTIF);
      enc_wrgreg(priv, ENC_EIE,  EIE_INTIE  | EIE_PKTIE  | EIE_LINKIE |
                                 EIE_TXIE   | EIE_TXERIE | EIE_RXERIE);

      /* Enable the receiver */

      enc_bfsgreg(priv, ENC_ECON1, ECON1_RXEN);

      /* Set and activate a timer process */

      (void)wd_start(priv->txpoll, ENC_WDDELAY, enc_polltimer, 1, (uint32_t)priv);

      /* Mark the interface up and enable the Ethernet interrupt at the
       * controller
       */

      priv->bifup = true;
      up_enable_irq(priv->irq);
    }
  return ret;
}

/****************************************************************************
 * Function: enc_ifdown
 *
 * Description:
 *   NuttX Callback: Stop the interface.
 *
 * Parameters:
 *   dev  - Reference to the NuttX driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_ifdown(struct uip_driver_s *dev)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)dev->d_private;
  irqstate_t flags;
  int ret;

  nlldbg("Taking down: %d.%d.%d.%d\n",
       dev->d_ipaddr & 0xff, (dev->d_ipaddr >> 8) & 0xff,
       (dev->d_ipaddr >> 16) & 0xff, dev->d_ipaddr >> 24 );

  /* Disable the Ethernet interrupt */

  flags = irqsave();
  up_disable_irq(priv->irq);

  /* Cancel the TX poll timer and TX timeout timers */

  wd_cancel(priv->txpoll);
  wd_cancel(priv->txtimeout);

  /* Reset the device and leave in the power save state */

  ret = enc_reset(priv);
  enc_pwrsave(priv);

  priv->bifup = false;
  irqrestore(flags);
  return ret;
}

/****************************************************************************
 * Function: enc_txavail
 *
 * Description:
 *   Driver callback invoked when new TX data is available.  This is a 
 *   stimulus perform an out-of-cycle poll and, thereby, reduce the TX
 *   latency.
 *
 * Parameters:
 *   dev  - Reference to the NuttX driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *   Called in normal user mode
 *
 ****************************************************************************/

static int enc_txavail(struct uip_driver_s *dev)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)dev->d_private;
  irqstate_t flags;

  flags = irqsave();

  /* Ignore the notification if the interface is not yet up */

  if (priv->bifup)
    {
      /* Check if the hardware is ready to send another packet.  The driver
       * starts a transmission process by setting ECON1.TXRTS. When the packet is
       * finished transmitting or is aborted due to an error/cancellation, the
       * ECON1.TXRTS bit will be cleared.
       */

      if ((enc_rdgreg(priv, ENC_ECON1) & ECON1_TXRTS) == 0)
        {
          /* The interface is up and TX is idle; poll uIP for new XMIT data */

          (void)uip_poll(&priv->dev, enc_uiptxpoll);
        }
    }

  irqrestore(flags);
  return OK;
}

/****************************************************************************
 * Function: enc_addmac
 *
 * Description:
 *   NuttX Callback: Add the specified MAC address to the hardware multicast
 *   address filtering
 *
 * Parameters:
 *   dev  - Reference to the NuttX driver state structure
 *   mac  - The MAC address to be added 
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

#ifdef CONFIG_NET_IGMP
static int enc_addmac(struct uip_driver_s *dev, FAR const uint8_t *mac)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)dev->d_private;

  /* Add the MAC address to the hardware multicast routing table */

#warning "Multicast MAC support not implemented"
  return OK;
}
#endif

/****************************************************************************
 * Function: enc_rmmac
 *
 * Description:
 *   NuttX Callback: Remove the specified MAC address from the hardware multicast
 *   address filtering
 *
 * Parameters:
 *   dev  - Reference to the NuttX driver state structure
 *   mac  - The MAC address to be removed 
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

#ifdef CONFIG_NET_IGMP
static int enc_rmmac(struct uip_driver_s *dev, FAR const uint8_t *mac)
{
  FAR struct enc_driver_s *priv = (FAR struct enc_driver_s *)dev->d_private;

  /* Add the MAC address to the hardware multicast routing table */

#warning "Multicast MAC support not implemented"
  return OK;
}
#endif

/****************************************************************************
 * Function: enc_pwrsave
 *
 * Description:
 *   The ENC28J60 may be commanded to power-down via the SPI interface.
 *   When powered down, it will no longer be able to transmit and receive
 *   any packets. To maximize power savings:
 *
 *   1. Turn off packet reception by clearing ECON1.RXEN.
 *   2. Wait for any in-progress packets to finish being received by
 *      polling ESTAT.RXBUSY. This bit should be clear before proceeding.
 *   3. Wait for any current transmissions to end by confirming ECON1.TXRTS
 *      is clear.
 *   4. Set ECON2.VRPS (if not already set).
 *   5. Enter Sleep by setting ECON2.PWRSV. All MAC, MII and PHY registers
 *      become inaccessible as a result. Setting PWRSV also clears
 *      ESTAT.CLKRDY automatically.
 *
 *   In Sleep mode, all registers and buffer memory will maintain their
 *   states. The ETH registers and buffer memory will still be accessible
 *   by the host controller. Additionally, the clock driver will continue
 *   to operate. The CLKOUT function will be unaffected.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_pwrsave(FAR struct enc_driver_s *priv)
{
  nllvdbg("Set PWRSV\n");

  /* 1. Turn off packet reception by clearing ECON1.RXEN. */

  enc_bfcgreg(priv, ENC_ECON1, ECON1_RXEN);

  /* 2. Wait for any in-progress packets to finish being received by
   *    polling ESTAT.RXBUSY. This bit should be clear before proceeding.
   */

  if (enc_waitbreg(priv, ENC_ESTAT, ESTAT_RXBUSY, 0) == OK)
    {
      /* 3. Wait for any current transmissions to end by confirming
       * ECON1.TXRTS is clear.
       */

      enc_waitbreg(priv, ENC_ECON1, ECON1_TXRTS, 0);

      /* 4. Set ECON2.VRPS (if not already set). */
      /* enc_bfsgreg(priv, ENC_ECON2, ECON2_VRPS); <-- Set in enc_reset() */

      /* 5. Enter Sleep by setting ECON2.PWRSV. */

      enc_bfsgreg(priv, ENC_ECON2, ECON2_PWRSV);
    }
}

/****************************************************************************
 * Function: enc_pwrfull
 *
 * Description:
 *   When normal operation is desired, the host controller must perform
 *   a slightly modified procedure:
 *
 *   1. Wake-up by clearing ECON2.PWRSV.
 *   2. Wait at least 300 <EFBFBD>s for the PHY to stabilize. To accomplish the
 *      delay, the host controller may poll ESTAT.CLKRDY and wait for it
 *      to become set.
 *   3. Restore receive capability by setting ECON1.RXEN.
 *
 *   After leaving Sleep mode, there is a delay of many milliseconds
 *   before a new link is established (assuming an appropriate link
 *   partner is present). The host controller may wish to wait until
 *   the link is established before attempting to transmit any packets.
 *   The link status can be determined by polling the PHSTAT2.LSTAT bit.
 *   Alternatively, the link change interrupt may be used if it is
 *   enabled.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/
 
static void enc_pwrfull(FAR struct enc_driver_s *priv)
{
  nllvdbg("Clear PWRSV\n");

  /* 1. Wake-up by clearing ECON2.PWRSV. */

  enc_bfcgreg(priv, ENC_ECON2, ECON2_PWRSV);
  
  /* 2. Wait at least 300 <20>s for the PHY to stabilize. To accomplish the
   * delay, the host controller may poll ESTAT.CLKRDY and wait for it to
   * become set.
   */

  enc_waitbreg(priv, ENC_ESTAT, ESTAT_CLKRDY, ESTAT_CLKRDY);

  /* 3. Restore receive capability by setting ECON1.RXEN.
   *
   * The caller will do this when it is read to receive packets
   */
}

/****************************************************************************
 * Function: enc_setmacaddr
 *
 * Description:
 *   Set the MAC address to the configured value.  This is done after ifup
 *   or after a TX timeout.  Note that this means that the interface must
 *   be down before configuring the MAC addr.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static void enc_setmacaddr(FAR struct enc_driver_s *priv)
{
  /* Program the hardware with it's MAC address (for filtering) */

  enc_wrbreg(priv, ENC_MAADR1, priv->dev.d_mac.ether_addr_octet[5]);
  enc_wrbreg(priv, ENC_MAADR2, priv->dev.d_mac.ether_addr_octet[4]);
  enc_wrbreg(priv, ENC_MAADR3, priv->dev.d_mac.ether_addr_octet[3]);
  enc_wrbreg(priv, ENC_MAADR4, priv->dev.d_mac.ether_addr_octet[2]);
  enc_wrbreg(priv, ENC_MAADR5, priv->dev.d_mac.ether_addr_octet[1]);
  enc_wrbreg(priv, ENC_MAADR6, priv->dev.d_mac.ether_addr_octet[0]);
}

/****************************************************************************
 * Function: enc_reset
 *
 * Description:
 *   Stop, reset, re-initialize, and restart the ENC28J60.  This is done
 *   initially, on ifup, and after a TX timeout.
 *
 * Parameters:
 *   priv  - Reference to the driver state structure
 *
 * Returned Value:
 *   None
 *
 * Assumptions:
 *
 ****************************************************************************/

static int enc_reset(FAR struct enc_driver_s *priv)
{
  uint8_t regval;

  nlldbg("Reset\n");

  /* Configure SPI for the ENC28J60 */

  enc_configspi(priv->spi);

  /* Reset the ENC28J60 */

  enc_wrgreg(priv, ENC_SRC, ENC_SRC);

  /* Check CLKRDY bit to see when the reset is complete.  There is an errata
   * that says the CLKRDY may be invalid.  We'll wait a couple of msec to
   * workaround this condition.
   */

  up_mdelay(2);
  /* while ((enc_rdgreg(priv, ENC_ESTAT) & ESTAT_CLKRDY) != 0); */

  /* Initialize ECON1: Clear ECON1 */

  enc_wrgreg(priv, ENC_ECON1, 0x00);

  /* Initialize ECON2: Enable address auto increment and voltage
   * regulator powersave.
   */

  enc_wrgreg(priv, ENC_ECON2, ECON2_AUTOINC | ECON2_VRPS);

  /* Initialize receive buffer.
   * First, set the receive buffer start address.
   */

  priv->nextpkt = PKTMEM_RX_START;
  enc_wrbreg(priv, ENC_ERXSTL, PKTMEM_RX_START & 0xff);
  enc_wrbreg(priv, ENC_ERXSTH, PKTMEM_RX_START >> 8);

  /* Set the receive data pointer */

  enc_wrbreg(priv, ENC_ERXRDPTL, PKTMEM_RX_START & 0xff);
  enc_wrbreg(priv, ENC_ERXRDPTH, PKTMEM_RX_START >> 8);

  /* Set the receive buffer end. */

  enc_wrbreg(priv, ENC_ERXNDL, PKTMEM_RX_END & 0xff);
  enc_wrbreg(priv, ENC_ERXNDH, PKTMEM_RX_END >> 8);

  /* Set transmit buffer start. */

  enc_wrbreg(priv, ENC_ETXSTL, PKTMEM_TX_START & 0xff);
  enc_wrbreg(priv, ENC_ETXSTH, PKTMEM_TX_START >> 8);

  /* Check if we are actually communicating with the ENC28J60.  If its
   * 0x00 or 0xff, then we are probably not communicating correctly
   * via SPI.
   */

  regval = enc_rdbreg(priv, ENC_EREVID);
  if (regval == 0x00 || regval == 0xff)
    {
      nlldbg("Bad Rev ID: %02x\n", regval);
      return -ENODEV;
    }
  nllvdbg("Rev ID: %02x\n", regval);

  /* Set filter mode: unicast OR broadcast AND crc valid */

  enc_wrbreg(priv, ENC_ERXFCON, ERXFCON_UCEN | ERXFCON_CRCEN | ERXFCON_BCEN);

  /* Enable MAC receive */

  enc_wrbreg(priv, ENC_MACON1, MACON1_MARXEN | MACON1_TXPAUS | MACON1_RXPAUS);

  /* Enable automatic padding and CRC operations */

#ifdef CONFIG_ENC28J60_HALFDUPLEX
  enc_wrbreg(priv, ENC_MACON3, MACON3_PADCFG0 | MACON3_TXCRCEN | MACON3_FRMLNEN);
  enc_wrbreg(priv, ENC_MACON4, MACON4_DEFER);        /* Defer transmission enable */

  /* Set Non-Back-to-Back Inter-Packet Gap */

  enc_wrbreg(priv, ENC_MAIPGL, 0x12);
  enc_wrbreg(priv, ENC_MAIPGH, 0x0c);

  /* Set Back-to-Back Inter-Packet Gap */
 
  enc_wrbreg(priv, ENC_MABBIPG, 0x12);
#else
  /* Set filter mode: unicast OR broadcast AND crc valid AND Full Duplex */

  enc_wrbreg(priv, ENC_MACON3,
             MACON3_PADCFG0 | MACON3_TXCRCEN | MACON3_FRMLNEN | MACON3_FULDPX);

  /* Set Non-Back-to-Back Inter-Packet Gap */

  enc_wrbreg(priv, ENC_MAIPGL, 0x12);

  /* Set ack-to-Back Inter-Packet Gap */

  enc_wrbreg(priv, ENC_MABBIPG, 0x15);
#endif

  /* Set the maximum packet size which the controller will accept */

  enc_wrbreg(priv, ENC_MAMXFLL, CONFIG_NET_BUFSIZE & 0xff);
  enc_wrbreg(priv, ENC_MAMXFLH, CONFIG_NET_BUFSIZE >> 8);

  /* Configure LEDs (No, just use the defaults for now) */
  /* enc_wrphy(priv, ENC_PHLCON, ??); */

  /* Setup up PHCON1 & 2 */
  
#ifdef CONFIG_ENC28J60_HALFDUPLEX
  enc_wrphy(priv, ENC_PHCON1, 0x00);
  enc_wrphy(priv, ENC_PHCON2, PHCON2_HDLDIS);
#else
  enc_wrphy(priv, ENC_PHCON1, PHCON1_PDPXMD);
  enc_wrphy(priv, ENC_PHCON2, 0x00);
#endif
  return OK;
}

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

/****************************************************************************
 * Function: enc_initialize
 *
 * Description:
 *   Initialize the Ethernet driver.  The ENC28J60 device is assumed to be
 *   in the post-reset state upon entry to this function.
 *
 * Parameters:
 *   spi   - A reference to the platform's SPI driver for the ENC28J60
 *   devno - If more than one ENC28J60 is supported, then this is the
 *           zero based number that identifies the ENC28J60;
 *   irq   - The fully configured GPIO IRQ that ENC28J60 interrupts will be
 *           asserted on.  This driver will attach and entable this IRQ.
 *
 * Returned Value:
 *   OK on success; Negated errno on failure.
 *
 * Assumptions:
 *
 ****************************************************************************/

int enc_initialize(FAR struct spi_dev_s *spi, unsigned int devno, unsigned int irq)
{
  FAR struct enc_driver_s *priv ;
  int ret;

  DEBUGASSERT(devno < CONFIG_ENC28J60_NINTERFACES);
  priv = &g_enc28j60[devno];

  /* Initialize the driver structure */

  memset(g_enc28j60, 0, CONFIG_ENC28J60_NINTERFACES*sizeof(struct enc_driver_s));
  priv->dev.d_ifup    = enc_ifup;     /* I/F down callback */
  priv->dev.d_ifdown  = enc_ifdown;   /* I/F up (new IP address) callback */
  priv->dev.d_txavail = enc_txavail;  /* New TX data callback */
#ifdef CONFIG_NET_IGMP
  priv->dev.d_addmac  = enc_addmac;   /* Add multicast MAC address */
  priv->dev.d_rmmac   = enc_rmmac;    /* Remove multicast MAC address */
#endif
  priv->dev.d_private = priv;         /* Used to recover private state from dev */

  /* Create a watchdog for timing polling for and timing of transmisstions */

  priv->txpoll       = wd_create();   /* Create periodic poll timer */
  priv->txtimeout    = wd_create();   /* Create TX timeout timer */
  priv->spi          = spi;           /* Save the SPI instance */
  priv->irq          = irq;           /* Save the IRQ number */

  /* Make sure that the interface is in the down state.  NOTE:  The MAC
   * address will not be set up until ifup.  That gives the app time to set
   * the MAC address before bringing the interface up.
   */

  ret = enc_ifdown(&priv->dev);
  if (ret == OK)
    {
      /* Attach the IRQ to the driver (but don't enable it yet) */

      if (irq_attach(irq, enc_interrupt))
        {
          /* We could not attach the ISR to the interrupt */

          ret =  -EAGAIN;
        }

      /* Register the device with the OS so that socket IOCTLs can be performed */

      (void)netdev_register(&priv->dev);
    }
  return ret;
}

/****************************************************************************
 * Function: enc_stats
 *
 * Description:
 *   Return accumulated ENC28J60 statistics.  Statistics are cleared after
 *   being returned.
 *
 * Parameters:
 *   devno - If more than one ENC28J60 is supported, then this is the
 *           zero based number that identifies the ENC28J60;
 *   stats - The user-provided location to return the statistics.
 *
 * Returned Value:
 *   OK on success; Negated errno on failure.
 *
 * Assumptions:
 *
 ****************************************************************************/

#ifdef CONFIG_ENC28J60_STATS
int enc_stats(unsigned int devno, struct enc_stats_s *stats)
{
  FAR struct enc_driver_s *priv ;
  irqstate_t flags;

  DEBUGASSERT(devno < CONFIG_ENC28J60_NINTERFACES);
  priv = &g_enc28j60[devno];

  /* Disable the Ethernet interrupt */

  flags = irqsave();
  memcpy(stats, &priv->stats, sizeof(struct enc_stats_s));
  memset(&priv->stats, 0, sizeof(struct enc_stats_s));
  irqrestore(flags);
  return OK;
}
#endif
#endif /* CONFIG_NET && CONFIG_ENC28J60_NET */