/* * Copyright (C) 2015 INRIA * Copyright (C) 2016 Freie Universität Berlin * * This file is subject to the terms and conditions of the GNU Lesser * General Public License v2.1. See the file LICENSE in the top level * directory for more details. */ /** * @{ * @ingroup net_csma_sender * @file * @brief Implementation of the CSMA/CA helper * * @author Kévin Roussel * @author Martine Lenders * @} */ #include #include #include #include "xtimer.h" #include "random.h" #include "net/netdev2.h" #include "net/netopt.h" #include "net/csma_sender.h" #define ENABLE_DEBUG (0) #include "debug.h" #if ENABLE_DEBUG /* For PRIu16 etc. */ #include #endif const csma_sender_conf_t CSMA_SENDER_CONF_DEFAULT = { CSMA_SENDER_MIN_BE_DEFAULT, CSMA_SENDER_MAX_BE_DEFAULT, CSMA_SENDER_MAX_BACKOFFS_DEFAULT, CSMA_SENDER_BACKOFF_PERIOD_UNIT }; /*--------------------- "INTERNAL" UTILITY FUNCTIONS ---------------------*/ /** * @brief choose an adequate random backoff period in microseconds, * from the given Backoff Exponent * * @param[in] be Backoff Exponent for the computation of period * * @return An adequate random backoff exponent in microseconds */ static inline uint32_t choose_backoff_period(int be, const csma_sender_conf_t *conf) { if (be < conf->min_be) { be = conf->min_be; } if (be > conf->max_be) { be = conf->max_be; } uint32_t max_backoff = ((1 << be) - 1) * CSMA_SENDER_BACKOFF_PERIOD_UNIT; uint32_t period = random_uint32() % max_backoff; if (period < CSMA_SENDER_BACKOFF_PERIOD_UNIT) { period = CSMA_SENDER_BACKOFF_PERIOD_UNIT; } return period; } /** * @brief Perform a CCA and send the given packet if medium is available * * @param[in] device netdev device, needs to be already initialized * @param[in] vector pointer to the data * @param[in] count number of elements in @p vector * * @return the return value of device driver's * netdev2_driver_t::send() function if medium was * available * @return -ECANCELED if an internal driver error occurred * @return -EBUSY if radio medium was not available * to send the given data */ static int send_if_cca(netdev2_t *device, struct iovec *vector, unsigned count) { netopt_enable_t hwfeat; /* perform a CCA */ DEBUG("csma: Checking radio medium availability...\n"); int res = device->driver->get(device, NETOPT_IS_CHANNEL_CLR, (void *) &hwfeat, sizeof(netopt_enable_t)); if (res < 0) { /* normally impossible: we got a big internal problem! */ DEBUG("csma: !!! DEVICE DRIVER FAILURE! TRANSMISSION ABORTED!\n"); return -ECANCELED; } /* if medium is clear, send the packet and return */ if (hwfeat == NETOPT_ENABLE) { DEBUG("csma: Radio medium available: sending packet.\n"); return device->driver->send(device, vector, count); } /* if we arrive here, medium was not available for transmission */ DEBUG("csma: Radio medium busy.\n"); return -EBUSY; } /*------------------------- "EXPORTED" FUNCTIONS -------------------------*/ int csma_sender_csma_ca_send(netdev2_t *dev, struct iovec *vector, unsigned count, const csma_sender_conf_t *conf) { netopt_enable_t hwfeat; assert(dev); /* choose default configuration if none is given */ if (conf == NULL) { conf = &CSMA_SENDER_CONF_DEFAULT; } /* Does the transceiver do automatic CSMA/CA when sending? */ int res = dev->driver->get(dev, NETOPT_CSMA, (void *) &hwfeat, sizeof(netopt_enable_t)); bool ok = false; switch (res) { case -ENODEV: /* invalid device pointer given */ return -ENODEV; case -ENOTSUP: /* device doesn't make auto-CSMA/CA */ break; case -EOVERFLOW: /* (normally impossible...*/ case -ECANCELED: DEBUG("csma: !!! DEVICE DRIVER FAILURE! TRANSMISSION ABORTED!\n"); /* internal driver error! */ return -ECANCELED; default: ok = (hwfeat == NETOPT_ENABLE); } if (ok) { /* device does CSMA/CA all by itself: let it do its job */ DEBUG("csma: Network device does hardware CSMA/CA\n"); return dev->driver->send(dev, vector, count); } /* if we arrive here, then we must perform the CSMA/CA procedure ourselves by software */ random_init(_xtimer_now()); DEBUG("csma: Starting software CSMA/CA....\n"); int nb = 0, be = conf->min_be; while (nb <= conf->max_be) { /* delay for an adequate random backoff period */ uint32_t bp = choose_backoff_period(be, conf); xtimer_usleep(bp); /* try to send after a CCA */ res = send_if_cca(dev, vector, count); if (res >= 0) { /* TX done */ return res; } else if (res != -EBUSY) { /* something has gone wrong, return the error code */ return res; } /* medium is busy: increment CSMA counters */ DEBUG("csma: Radio medium busy.\n"); be++; if (be > conf->max_be) { be = conf->max_be; } nb++; /* ... and try again if we have no exceeded the retry limit */ } /* if we arrive here, medium was never available for transmission */ DEBUG("csma: Software CSMA/CA failure: medium never available.\n"); return -EBUSY; } int csma_sender_cca_send(netdev2_t *dev, struct iovec *vector, unsigned count) { netopt_enable_t hwfeat; assert(dev); /* Does the transceiver do automatic CCA before sending? */ int res = dev->driver->get(dev, NETOPT_AUTOCCA, (void *) &hwfeat, sizeof(netopt_enable_t)); bool ok = false; switch (res) { case -ENODEV: /* invalid device pointer given */ return -ENODEV; case -ENOTSUP: /* device doesn't make auto-CCA */ break; case -EOVERFLOW: /* (normally impossible...*/ case -ECANCELED: /* internal driver error! */ DEBUG("csma: !!! DEVICE DRIVER FAILURE! TRANSMISSION ABORTED!\n"); return -ECANCELED; default: ok = (hwfeat == NETOPT_ENABLE); } if (ok) { /* device does auto-CCA: let him do its job */ DEBUG("csma: Network device does auto-CCA checking.\n"); return dev->driver->send(dev, vector, count); } /* if we arrive here, we must do CCA ourselves to see if radio medium is clear before sending */ res = send_if_cca(dev, vector, count); if (res == -EBUSY) { DEBUG("csma: Transmission cancelled!\n"); } return res; }