osd-contiki/dev/cc2420/cc2420.c

/*
 * Copyright (c) 2007, Swedish Institute of Computer Science
 * All rights reserved.
 *
 * 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 of the Institute 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 INSTITUTE 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 INSTITUTE 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.
 *
 * This file is part of the Contiki operating system.
 *
 */
/*
 * This code is almost device independent and should be easy to port.
 */

#include <string.h>

#include "contiki.h"

#if defined(__AVR__)
#include <avr/io.h>
#endif

#include "dev/leds.h"
#include "dev/spi.h"
#include "cc2420.h"
#include "cc2420_const.h"

#include "net/packetbuf.h"
#include "net/rime/rimestats.h"
#include "net/netstack.h"

#define WITH_SEND_CCA 1

#define FOOTER_LEN 2

#ifndef CC2420_CONF_CHECKSUM
#define CC2420_CONF_CHECKSUM 0
#endif /* CC2420_CONF_CHECKSUM */

#ifndef CC2420_CONF_CHANNEL
#define CC2420_CONF_CHANNEL 26
#endif /* CC2420_CONF_CHANNEL */

#ifndef CC2420_CONF_CCA_THRESH
#define CC2420_CONF_CCA_THRESH -45
#endif /* CC2420_CONF_CCA_THRESH */


#ifndef CC2420_CONF_AUTOACK
#define CC2420_CONF_AUTOACK 0
#endif /* CC2420_CONF_AUTOACK */

#if CC2420_CONF_CHECKSUM
#include "lib/crc16.h"
#define CHECKSUM_LEN 2
#else
#define CHECKSUM_LEN 0
#endif /* CC2420_CONF_CHECKSUM */

#define AUX_LEN (CHECKSUM_LEN + FOOTER_LEN)


#define FOOTER1_CRC_OK      0x80
#define FOOTER1_CORRELATION 0x7f

/* The RSSI_OFFSET is approximate -45 (see CC2420 specification) */
#define RSSI_OFFSET -45

#define DEBUG 0
#if DEBUG
#include <stdio.h>
#define PRINTF(...) printf(__VA_ARGS__)
#else
#define PRINTF(...) do {} while (0)
#endif

#define DEBUG_LEDS DEBUG
#undef LEDS_ON
#undef LEDS_OFF
#if DEBUG_LEDS
#define LEDS_ON(x) leds_on(x)
#define LEDS_OFF(x) leds_off(x)
#else
#define LEDS_ON(x)
#define LEDS_OFF(x)
#endif

/* Conversion map between PA_LEVEL and output power in dBm
   (from table 9 in CC2420 specification).
*/
struct output_config {
  int8_t power;
  uint8_t config;
};

static const struct output_config output_power[] = {
  {  0, 31 }, /* 0xff */
  { -1, 27 }, /* 0xfb */
  { -3, 23 }, /* 0xf7 */
  { -5, 19 }, /* 0xf3 */
  { -7, 15 }, /* 0xef */
  {-10, 11 }, /* 0xeb */
  {-15,  7 }, /* 0xe7 */
  {-25,  3 }, /* 0xe3 */
};
#define OUTPUT_NUM (sizeof(output_power) / sizeof(struct output_config))
#define OUTPUT_POWER_MAX   0
#define OUTPUT_POWER_MIN -25

void cc2420_arch_init(void);

/* XXX hack: these will be made as Chameleon packet attributes */
rtimer_clock_t cc2420_time_of_arrival, cc2420_time_of_departure;

int cc2420_authority_level_of_sender;

int cc2420_packets_seen, cc2420_packets_read;

/* static uint8_t volatile pending; */

#define BUSYWAIT_UNTIL(cond, max_time)                                  \
  do {                                                                  \
    rtimer_clock_t t0;                                                  \
    t0 = RTIMER_NOW();                                                  \
    while(!(cond) && RTIMER_CLOCK_LT(RTIMER_NOW(), t0 + (max_time)));   \
  } while(0)

volatile uint8_t cc2420_sfd_counter;
volatile uint16_t cc2420_sfd_start_time;
volatile uint16_t cc2420_sfd_end_time;

static volatile uint16_t last_packet_timestamp;
/*---------------------------------------------------------------------------*/
PROCESS(cc2420_process, "CC2420 driver");
/*---------------------------------------------------------------------------*/


int cc2420_on(void);
int cc2420_off(void);

static int cc2420_read(void *buf, unsigned short bufsize);

static int cc2420_prepare(const void *data, unsigned short len);
static int cc2420_transmit(unsigned short len);
static int cc2420_send(const void *data, unsigned short len);

static int cc2420_receiving_packet(void);
static int pending_packet(void);
static int cc2420_cca(void);
/*static int detected_energy(void);*/

signed char cc2420_last_rssi;
uint8_t cc2420_last_correlation;

static uint8_t receive_on;
static int channel;

static radio_result_t
get_value(radio_param_t param, radio_value_t *value)
{
  int i, v;

  if(!value) {
    return RADIO_RESULT_INVALID_VALUE;
  }
  switch(param) {
  case RADIO_PARAM_POWER_MODE:
    *value = receive_on ? RADIO_POWER_MODE_ON : RADIO_POWER_MODE_OFF;
    return RADIO_RESULT_OK;
  case RADIO_PARAM_CHANNEL:
    *value = cc2420_get_channel();
    return RADIO_RESULT_OK;
  case RADIO_PARAM_TXPOWER:
    v = cc2420_get_txpower();
    *value = OUTPUT_POWER_MIN;
    /* Find the actual estimated output power in conversion table */
    for(i = 0; i < OUTPUT_NUM; i++) {
      if(v >= output_power[i].config) {
        *value = output_power[i].power;
        break;
      }
    }
    return RADIO_RESULT_OK;
  case RADIO_PARAM_RSSI:
    /* Return the RSSI value in dBm */
    *value = cc2420_rssi() + RSSI_OFFSET;
    return RADIO_RESULT_OK;
  case RADIO_CONST_CHANNEL_MIN:
    *value = 11;
    return RADIO_RESULT_OK;
  case RADIO_CONST_CHANNEL_MAX:
    *value = 26;
    return RADIO_RESULT_OK;
  case RADIO_CONST_TXPOWER_MIN:
    *value = OUTPUT_POWER_MIN;
    return RADIO_RESULT_OK;
  case RADIO_CONST_TXPOWER_MAX:
    *value = OUTPUT_POWER_MAX;
    return RADIO_RESULT_OK;
  default:
    return RADIO_RESULT_NOT_SUPPORTED;
  }
}

static radio_result_t
set_value(radio_param_t param, radio_value_t value)
{
  int i;

  switch(param) {
  case RADIO_PARAM_POWER_MODE:
    if(value == RADIO_POWER_MODE_ON) {
      cc2420_on();
      return RADIO_RESULT_OK;
    }
    if(value == RADIO_POWER_MODE_OFF) {
      cc2420_off();
      return RADIO_RESULT_OK;
    }
    return RADIO_RESULT_INVALID_VALUE;
  case RADIO_PARAM_CHANNEL:
    if(value < 11 || value > 26) {
      return RADIO_RESULT_INVALID_VALUE;
    }
    cc2420_set_channel(value);
    return RADIO_RESULT_OK;
  case RADIO_PARAM_TXPOWER:
    if(value < OUTPUT_POWER_MIN || value > OUTPUT_POWER_MAX) {
      return RADIO_RESULT_INVALID_VALUE;
    }
    /* Find the closest higher PA_LEVEL for the desired output power */
    for(i = 1; i < OUTPUT_NUM; i++) {
      if(value > output_power[i].power) {
        break;
      }
    }
    cc2420_set_txpower(output_power[i - 1].config);
    return RADIO_RESULT_OK;
  default:
    return RADIO_RESULT_NOT_SUPPORTED;
  }
}

static radio_result_t
get_object(radio_param_t param, void *dest, size_t size)
{
  return RADIO_RESULT_NOT_SUPPORTED;
}

static radio_result_t
set_object(radio_param_t param, const void *src, size_t size)
{
  return RADIO_RESULT_NOT_SUPPORTED;
}

const struct radio_driver cc2420_driver =
  {
    cc2420_init,
    cc2420_prepare,
    cc2420_transmit,
    cc2420_send,
    cc2420_read,
    /* cc2420_set_channel, */
    /* detected_energy, */
    cc2420_cca,
    cc2420_receiving_packet,
    pending_packet,
    cc2420_on,
    cc2420_off,
    get_value,
    set_value,
    get_object,
    set_object
  };

/*---------------------------------------------------------------------------*/
static void
strobe(enum cc2420_register regname)
{
  CC2420_STROBE(regname);
}
/*---------------------------------------------------------------------------*/

static void
getrxdata(void *buf, int len)
{
  CC2420_READ_FIFO_BUF(buf, len);
}
static void
getrxbyte(uint8_t *byte)
{
  CC2420_READ_FIFO_BYTE(*byte);
}
static void
flushrx(void)
{
  uint8_t dummy;

  getrxbyte(&dummy);
  strobe(CC2420_SFLUSHRX);
  strobe(CC2420_SFLUSHRX);
  if(dummy) {
    /* avoid unused variable compiler warning */
  }
}
/*---------------------------------------------------------------------------*/
static unsigned int
status(void)
{
  uint8_t status;
  CC2420_GET_STATUS(status);
  return status;
}
/*---------------------------------------------------------------------------*/
static void
wait_for_status(unsigned int mask)
{
  BUSYWAIT_UNTIL((status() & mask), RTIMER_SECOND / 10);
}
/*---------------------------------------------------------------------------*/
static void
wait_for_not_status(unsigned int mask)
{
  BUSYWAIT_UNTIL(!(status() & mask), RTIMER_SECOND / 10);
}
/*---------------------------------------------------------------------------*/
static uint8_t locked, lock_on, lock_off;

static void
on(void)
{
  CC2420_ENABLE_FIFOP_INT();
  strobe(CC2420_SRXON);

  wait_for_status(BV(CC2420_XOSC16M_STABLE));

  ENERGEST_ON(ENERGEST_TYPE_LISTEN);
  receive_on = 1;
}
static void
off(void)
{
  /*  PRINTF("off\n");*/
  receive_on = 0;

  /* Wait for transmission to end before turning radio off. */
  wait_for_not_status(BV(CC2420_TX_ACTIVE));

  ENERGEST_OFF(ENERGEST_TYPE_LISTEN);
  strobe(CC2420_SRFOFF);
  CC2420_DISABLE_FIFOP_INT();

  if(!CC2420_FIFOP_IS_1) {
    flushrx();
  }
}
/*---------------------------------------------------------------------------*/
#define GET_LOCK() locked++
static void RELEASE_LOCK(void) {
  if(locked == 1) {
    if(lock_on) {
      on();
      lock_on = 0;
    }
    if(lock_off) {
      off();
      lock_off = 0;
    }
  }
  locked--;
}
/*---------------------------------------------------------------------------*/
static unsigned
getreg(enum cc2420_register regname)
{
  unsigned reg;
  CC2420_READ_REG(regname, reg);
  return reg;
}
/*---------------------------------------------------------------------------*/
static void
setreg(enum cc2420_register regname, unsigned value)
{
  CC2420_WRITE_REG(regname, value);
}
/*---------------------------------------------------------------------------*/
static void
write_ram(const void *buf, uint16_t addr, int count)
{
  CC2420_WRITE_RAM(buf, addr, count);
}
/*---------------------------------------------------------------------------*/
static void
set_txpower(uint8_t power)
{
  uint16_t reg;

  reg = getreg(CC2420_TXCTRL);
  reg = (reg & 0xffe0) | (power & 0x1f);
  setreg(CC2420_TXCTRL, reg);
}
/*---------------------------------------------------------------------------*/
#define AUTOACK (1 << 4)
#define ADR_DECODE (1 << 11)
#define RXFIFO_PROTECTION (1 << 9)
#define CORR_THR(n) (((n) & 0x1f) << 6)
#define FIFOP_THR(n) ((n) & 0x7f)
#define RXBPF_LOCUR (1 << 13);
/*---------------------------------------------------------------------------*/
int
cc2420_init(void)
{
  uint16_t reg;
  {
    int s = splhigh();
    cc2420_arch_init();		/* Initalize ports and SPI. */
    CC2420_DISABLE_FIFOP_INT();
    CC2420_FIFOP_INT_INIT();
    splx(s);
  }

  /* Turn on voltage regulator and reset. */
  SET_VREG_ACTIVE();
  clock_delay(250);
  SET_RESET_ACTIVE();
  clock_delay(127);
  SET_RESET_INACTIVE();
  clock_delay(125);


  /* Turn on the crystal oscillator. */
  strobe(CC2420_SXOSCON);

  /* Turn on/off automatic packet acknowledgment and address decoding. */
  reg = getreg(CC2420_MDMCTRL0);

#if CC2420_CONF_AUTOACK
  reg |= AUTOACK | ADR_DECODE;
#else
  reg &= ~(AUTOACK | ADR_DECODE);
#endif /* CC2420_CONF_AUTOACK */
  setreg(CC2420_MDMCTRL0, reg);

  /* Set transmission turnaround time to the lower setting (8 symbols
     = 0.128 ms) instead of the default (12 symbols = 0.192 ms). */
  /*  reg = getreg(CC2420_TXCTRL);
  reg &= ~(1 << 13);
  setreg(CC2420_TXCTRL, reg);*/

  
  /* Change default values as recomended in the data sheet, */
  /* correlation threshold = 20, RX bandpass filter = 1.3uA. */
  setreg(CC2420_MDMCTRL1, CORR_THR(20));
  reg = getreg(CC2420_RXCTRL1);
  reg |= RXBPF_LOCUR;
  setreg(CC2420_RXCTRL1, reg);

  /* Set the FIFOP threshold to maximum. */
  setreg(CC2420_IOCFG0, FIFOP_THR(127));

  /* Turn off "Security enable" (page 32). */
  reg = getreg(CC2420_SECCTRL0);
  reg &= ~RXFIFO_PROTECTION;
  setreg(CC2420_SECCTRL0, reg);

  cc2420_set_pan_addr(0xffff, 0x0000, NULL);
  cc2420_set_channel(CC2420_CONF_CHANNEL);
  cc2420_set_cca_threshold(CC2420_CONF_CCA_THRESH);

  flushrx();

  process_start(&cc2420_process, NULL);
  return 1;
}
/*---------------------------------------------------------------------------*/
static int
cc2420_transmit(unsigned short payload_len)
{
  int i, txpower;
#if CC2420_CONF_CHECKSUM
  uint16_t checksum;
#endif /* CC2420_CONF_CHECKSUM */

  GET_LOCK();

  txpower = 0;
  if(packetbuf_attr(PACKETBUF_ATTR_RADIO_TXPOWER) > 0) {
    /* Remember the current transmission power */
    txpower = cc2420_get_txpower();
    /* Set the specified transmission power */
    set_txpower(packetbuf_attr(PACKETBUF_ATTR_RADIO_TXPOWER) - 1);
  }

  /* The TX FIFO can only hold one packet. Make sure to not overrun
   * FIFO by waiting for transmission to start here and synchronizing
   * with the CC2420_TX_ACTIVE check in cc2420_send.
   *
   * Note that we may have to wait up to 320 us (20 symbols) before
   * transmission starts.
   */
#ifndef CC2420_CONF_SYMBOL_LOOP_COUNT
#error CC2420_CONF_SYMBOL_LOOP_COUNT needs to be set!!!
#else
#define LOOP_20_SYMBOLS CC2420_CONF_SYMBOL_LOOP_COUNT
#endif

#if WITH_SEND_CCA
  strobe(CC2420_SRXON);
  wait_for_status(BV(CC2420_RSSI_VALID));
  strobe(CC2420_STXONCCA);
#else /* WITH_SEND_CCA */
  strobe(CC2420_STXON);
#endif /* WITH_SEND_CCA */
  for(i = LOOP_20_SYMBOLS; i > 0; i--) {
    if(CC2420_SFD_IS_1) {
      {
        rtimer_clock_t sfd_timestamp;
        sfd_timestamp = cc2420_sfd_start_time;
        if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
           PACKETBUF_ATTR_PACKET_TYPE_TIMESTAMP) {
          /* Write timestamp to last two bytes of packet in TXFIFO. */
          write_ram(&sfd_timestamp, CC2420RAM_TXFIFO + payload_len - 1, 2);
        }
      }

      if(!(status() & BV(CC2420_TX_ACTIVE))) {
        /* SFD went high but we are not transmitting. This means that
           we just started receiving a packet, so we drop the
           transmission. */
        RELEASE_LOCK();
        return RADIO_TX_COLLISION;
      }
      if(receive_on) {
	ENERGEST_OFF(ENERGEST_TYPE_LISTEN);
      }
      ENERGEST_ON(ENERGEST_TYPE_TRANSMIT);
      /* We wait until transmission has ended so that we get an
	 accurate measurement of the transmission time.*/
      wait_for_not_status(BV(CC2420_TX_ACTIVE));

#ifdef ENERGEST_CONF_LEVELDEVICE_LEVELS
      ENERGEST_OFF_LEVEL(ENERGEST_TYPE_TRANSMIT,cc2420_get_txpower());
#endif
      ENERGEST_OFF(ENERGEST_TYPE_TRANSMIT);
      if(receive_on) {
	ENERGEST_ON(ENERGEST_TYPE_LISTEN);
      } else {
	/* We need to explicitly turn off the radio,
	 * since STXON[CCA] -> TX_ACTIVE -> RX_ACTIVE */
	off();
      }

      if(packetbuf_attr(PACKETBUF_ATTR_RADIO_TXPOWER) > 0) {
        /* Restore the transmission power */
        set_txpower(txpower & 0xff);
      }

      RELEASE_LOCK();
      return RADIO_TX_OK;
    }
  }

  /* If we are using WITH_SEND_CCA, we get here if the packet wasn't
     transmitted because of other channel activity. */
  RIMESTATS_ADD(contentiondrop);
  PRINTF("cc2420: do_send() transmission never started\n");

  if(packetbuf_attr(PACKETBUF_ATTR_RADIO_TXPOWER) > 0) {
    /* Restore the transmission power */
    set_txpower(txpower & 0xff);
  }

  RELEASE_LOCK();
  return RADIO_TX_COLLISION;
}
/*---------------------------------------------------------------------------*/
static int
cc2420_prepare(const void *payload, unsigned short payload_len)
{
  uint8_t total_len;
#if CC2420_CONF_CHECKSUM
  uint16_t checksum;
#endif /* CC2420_CONF_CHECKSUM */
  GET_LOCK();

  PRINTF("cc2420: sending %d bytes\n", payload_len);

  RIMESTATS_ADD(lltx);

  /* Wait for any previous transmission to finish. */
  /*  while(status() & BV(CC2420_TX_ACTIVE));*/

  /* Write packet to TX FIFO. */
  strobe(CC2420_SFLUSHTX);

#if CC2420_CONF_CHECKSUM
  checksum = crc16_data(payload, payload_len, 0);
#endif /* CC2420_CONF_CHECKSUM */
  total_len = payload_len + AUX_LEN;
  CC2420_WRITE_FIFO_BUF(&total_len, 1);
  CC2420_WRITE_FIFO_BUF(payload, payload_len);
#if CC2420_CONF_CHECKSUM
  CC2420_WRITE_FIFO_BUF(&checksum, CHECKSUM_LEN);
#endif /* CC2420_CONF_CHECKSUM */

  RELEASE_LOCK();
  return 0;
}
/*---------------------------------------------------------------------------*/
static int
cc2420_send(const void *payload, unsigned short payload_len)
{
  cc2420_prepare(payload, payload_len);
  return cc2420_transmit(payload_len);
}
/*---------------------------------------------------------------------------*/
int
cc2420_off(void)
{
  /* Don't do anything if we are already turned off. */
  if(receive_on == 0) {
    return 1;
  }

  /* If we are called when the driver is locked, we indicate that the
     radio should be turned off when the lock is unlocked. */
  if(locked) {
    /*    printf("Off when locked (%d)\n", locked);*/
    lock_off = 1;
    return 1;
  }

  GET_LOCK();
  /* If we are currently receiving a packet (indicated by SFD == 1),
     we don't actually switch the radio off now, but signal that the
     driver should switch off the radio once the packet has been
     received and processed, by setting the 'lock_off' variable. */
  if(status() & BV(CC2420_TX_ACTIVE)) {
    lock_off = 1;
  } else {
    off();
  }
  RELEASE_LOCK();
  return 1;
}
/*---------------------------------------------------------------------------*/
int
cc2420_on(void)
{
  if(receive_on) {
    return 1;
  }
  if(locked) {
    lock_on = 1;
    return 1;
  }

  GET_LOCK();
  on();
  RELEASE_LOCK();
  return 1;
}
/*---------------------------------------------------------------------------*/
int
cc2420_get_channel(void)
{
  return channel;
}
/*---------------------------------------------------------------------------*/
int
cc2420_set_channel(int c)
{
  uint16_t f;

  GET_LOCK();
  /*
   * Subtract the base channel (11), multiply by 5, which is the
   * channel spacing. 357 is 2405-2048 and 0x4000 is LOCK_THR = 1.
   */
  channel = c;

  f = 5 * (c - 11) + 357 + 0x4000;
  /*
   * Writing RAM requires crystal oscillator to be stable.
   */
  wait_for_status(BV(CC2420_XOSC16M_STABLE));

  /* Wait for any transmission to end. */
  wait_for_not_status(BV(CC2420_TX_ACTIVE));

  setreg(CC2420_FSCTRL, f);

  /* If we are in receive mode, we issue an SRXON command to ensure
     that the VCO is calibrated. */
  if(receive_on) {
    strobe(CC2420_SRXON);
  }

  RELEASE_LOCK();
  return 1;
}
/*---------------------------------------------------------------------------*/
void
cc2420_set_pan_addr(unsigned pan,
                    unsigned addr,
                    const uint8_t *ieee_addr)
{
  uint16_t f = 0;
  uint8_t tmp[2];

  GET_LOCK();
  
  /*
   * Writing RAM requires crystal oscillator to be stable.
   */
  wait_for_status(BV(CC2420_XOSC16M_STABLE));

  tmp[0] = pan & 0xff;
  tmp[1] = pan >> 8;
  write_ram(&tmp, CC2420RAM_PANID, 2);

  tmp[0] = addr & 0xff;
  tmp[1] = addr >> 8;
  write_ram(&tmp, CC2420RAM_SHORTADDR, 2);
  if(ieee_addr != NULL) {
    uint8_t tmp_addr[8];
    /* LSB first, MSB last for 802.15.4 addresses in CC2420 */
    for (f = 0; f < 8; f++) {
      tmp_addr[7 - f] = ieee_addr[f];
    }
    write_ram(tmp_addr, CC2420RAM_IEEEADDR, 8);
  }
  RELEASE_LOCK();
}
/*---------------------------------------------------------------------------*/
/*
 * Interrupt leaves frame intact in FIFO.
 */
int
cc2420_interrupt(void)
{
  CC2420_CLEAR_FIFOP_INT();
  process_poll(&cc2420_process);

  last_packet_timestamp = cc2420_sfd_start_time;
  /* pending++; */
  cc2420_packets_seen++;
  return 1;
}
/*---------------------------------------------------------------------------*/
PROCESS_THREAD(cc2420_process, ev, data)
{
  int len;
  PROCESS_BEGIN();

  PRINTF("cc2420_process: started\n");

  while(1) {
    PROCESS_YIELD_UNTIL(ev == PROCESS_EVENT_POLL);

    PRINTF("cc2420_process: calling receiver callback\n");

    packetbuf_clear();
    packetbuf_set_attr(PACKETBUF_ATTR_TIMESTAMP, last_packet_timestamp);
    len = cc2420_read(packetbuf_dataptr(), PACKETBUF_SIZE);
    
    packetbuf_set_datalen(len);
    
    NETSTACK_RDC.input();
  }

  PROCESS_END();
}
/*---------------------------------------------------------------------------*/
static int
cc2420_read(void *buf, unsigned short bufsize)
{
  uint8_t footer[2];
  uint8_t len;
#if CC2420_CONF_CHECKSUM
  uint16_t checksum;
#endif /* CC2420_CONF_CHECKSUM */

  if(!CC2420_FIFOP_IS_1) {
    return 0;
  }
  /*  if(!pending) {
    return 0;
    }*/
  
  /* pending = 0; */
  
  GET_LOCK();

  cc2420_packets_read++;

  getrxbyte(&len);

  if(len > CC2420_MAX_PACKET_LEN) {
    /* Oops, we must be out of sync. */
    flushrx();
    RIMESTATS_ADD(badsynch);
    RELEASE_LOCK();
    return 0;
  }

  if(len <= AUX_LEN) {
    flushrx();
    RIMESTATS_ADD(tooshort);
    RELEASE_LOCK();
    return 0;
  }

  if(len - AUX_LEN > bufsize) {
    flushrx();
    RIMESTATS_ADD(toolong);
    RELEASE_LOCK();
    return 0;
  }

  getrxdata(buf, len - AUX_LEN);
#if CC2420_CONF_CHECKSUM
  getrxdata(&checksum, CHECKSUM_LEN);
#endif /* CC2420_CONF_CHECKSUM */
  getrxdata(footer, FOOTER_LEN);

#if CC2420_CONF_CHECKSUM
  if(checksum != crc16_data(buf, len - AUX_LEN, 0)) {
    PRINTF("checksum failed 0x%04x != 0x%04x\n",
	   checksum, crc16_data(buf, len - AUX_LEN, 0));
  }

  if(footer[1] & FOOTER1_CRC_OK &&
     checksum == crc16_data(buf, len - AUX_LEN, 0)) {
#else
  if(footer[1] & FOOTER1_CRC_OK) {
#endif /* CC2420_CONF_CHECKSUM */
    cc2420_last_rssi = footer[0];
    cc2420_last_correlation = footer[1] & FOOTER1_CORRELATION;


    packetbuf_set_attr(PACKETBUF_ATTR_RSSI, cc2420_last_rssi);
    packetbuf_set_attr(PACKETBUF_ATTR_LINK_QUALITY, cc2420_last_correlation);

    RIMESTATS_ADD(llrx);

  } else {
    RIMESTATS_ADD(badcrc);
    len = AUX_LEN;
  }

  if(CC2420_FIFOP_IS_1) {
    if(!CC2420_FIFO_IS_1) {
      /* Clean up in case of FIFO overflow!  This happens for every
       * full length frame and is signaled by FIFOP = 1 and FIFO =
       * 0. */
      flushrx();
    } else {
      /* Another packet has been received and needs attention. */
      process_poll(&cc2420_process);
    }
  }

  RELEASE_LOCK();

  if(len < AUX_LEN) {
    return 0;
  }

  return len - AUX_LEN;
}
/*---------------------------------------------------------------------------*/
void
cc2420_set_txpower(uint8_t power)
{
  GET_LOCK();
  set_txpower(power);
  RELEASE_LOCK();
}
/*---------------------------------------------------------------------------*/
int
cc2420_get_txpower(void)
{
  int power;
  GET_LOCK();
  power = (int)(getreg(CC2420_TXCTRL) & 0x001f);
  RELEASE_LOCK();
  return power;
}
/*---------------------------------------------------------------------------*/
int
cc2420_rssi(void)
{
  int rssi;
  int radio_was_off = 0;

  if(locked) {
    return 0;
  }
  
  GET_LOCK();

  if(!receive_on) {
    radio_was_off = 1;
    cc2420_on();
  }
  wait_for_status(BV(CC2420_RSSI_VALID));

  rssi = (int)((signed char)getreg(CC2420_RSSI));

  if(radio_was_off) {
    cc2420_off();
  }
  RELEASE_LOCK();
  return rssi;
}
/*---------------------------------------------------------------------------*/
/*
static int
detected_energy(void)
{
  return cc2420_rssi();
}
*/
/*---------------------------------------------------------------------------*/
static int
cc2420_cca(void)
{
  int cca;
  int radio_was_off = 0;

  /* If the radio is locked by an underlying thread (because we are
     being invoked through an interrupt), we preted that the coast is
     clear (i.e., no packet is currently being transmitted by a
     neighbor). */
  if(locked) {
    return 1;
  }

  GET_LOCK();
  if(!receive_on) {
    radio_was_off = 1;
    cc2420_on();
  }

  /* Make sure that the radio really got turned on. */
  if(!receive_on) {
    RELEASE_LOCK();
    if(radio_was_off) {
      cc2420_off();
    }
    return 1;
  }

  wait_for_status(BV(CC2420_RSSI_VALID));

  cca = CC2420_CCA_IS_1;

  if(radio_was_off) {
    cc2420_off();
  }
  RELEASE_LOCK();
  return cca;
}
/*---------------------------------------------------------------------------*/
int
cc2420_receiving_packet(void)
{
  return CC2420_SFD_IS_1;
}
/*---------------------------------------------------------------------------*/
static int
pending_packet(void)
{
  return CC2420_FIFOP_IS_1;
}
/*---------------------------------------------------------------------------*/
void
cc2420_set_cca_threshold(int value)
{
  uint16_t shifted = value << 8;
  GET_LOCK();
  setreg(CC2420_RSSI, shifted);
  RELEASE_LOCK();
}
/*---------------------------------------------------------------------------*/