RIOT/drivers/cc110x/cc1100-csmaca-mac.c

/******************************************************************************
Copyright 2008, Freie Universitaet Berlin (FUB). All rights reserved.

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and Telematics group (http://cst.mi.fu-berlin.de).
-------------------------------------------------------------------------------
This file is part of FeuerWare.

This program is free software: you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
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FeuerWare is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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*******************************************************************************/

/**
 * @file
 * @ingroup		dev_cc110x
 * @brief		ScatterWeb MSB-A2 mac-layer
 *
 * @author      Freie Universität Berlin, Computer Systems & Telematics, FeuerWhere project
 * @author		Thomas Hillebrandt <hillebra@inf.fu-berlin.de>
 * @author		Heiko Will <hwill@inf.fu-berlin.de>
 * @version     $Revision: 2128 $
 *
 * @note    	$Id: cc1100-csmaca-mac.c 2128 2010-05-12 12:07:59Z hillebra $
 */

#include <stdio.h>
//#include <stdlib.h>
#include <string.h>

#include "cc1100.h"
#include "cc1100_phy.h"
#include "cc1100-csmaca-mac.h"
#include "protocol-multiplex.h"

#include "hwtimer.h"

/*---------------------------------------------------------------------------*/

#define COLLISION_STATE_INITIAL 1
#define COLLISION_STATE_MEASURE 2
#define COLLISION_STATE_KEEP    3

static uint32_t send_csmaca_calls = 0;
static uint32_t send_csmaca_calls_cs_timeout = 0;
static int collision_count;
static double collisions_per_sec = 0;
static int collision_state = COLLISION_STATE_INITIAL;
static uint64_t collision_measurement_start = 0;

volatile static int cs_hwtimer_id = -1;
volatile static int cs_timeout_flag = 0;

/*---------------------------------------------------------------------------*/
static void cs_timeout_cb(void* ptr)
{
	cs_timeout_flag = 1;
}

/*---------------------------------------------------------------------------*/
int cc1100_send_csmaca(radio_address_t address, protocol_t protocol, int priority, char *payload, int payload_len)
{
	uint16_t min_window_size;
	uint16_t max_window_size;
	uint16_t difs;
	uint16_t slottime;

	switch (priority)
	{
		case PRIORITY_ALARM:
			min_window_size = PRIO_ALARM_MIN_WINDOW_SIZE;
			max_window_size = PRIO_ALARM_MAX_WINDOW_SIZE;
			difs = PRIO_ALARM_DIFS;
			slottime = PRIO_ALARM_SLOTTIME;
			break;
		case PRIORITY_WARNING:
			min_window_size = PRIO_WARN_MIN_WINDOW_SIZE;
			max_window_size = PRIO_WARN_MAX_WINDOW_SIZE;
			difs = PRIO_WARN_DIFS;
			slottime = PRIO_WARN_SLOTTIME;
			break;
		default:
			min_window_size = PRIO_DATA_MIN_WINDOW_SIZE;
			max_window_size = PRIO_DATA_MAX_WINDOW_SIZE;
			difs = PRIO_DATA_DIFS;
			slottime = PRIO_DATA_SLOTTIME;
	}

	// Calculate collisions per second
	if (collision_state == COLLISION_STATE_INITIAL) {
		collision_measurement_start = swtimer_now();
		collision_count = 0;
		collisions_per_sec = 0;
		collision_state = COLLISION_STATE_MEASURE;
	} else if (collision_state == COLLISION_STATE_MEASURE) {
		uint64_t timespan = swtimer_now() - collision_measurement_start;
		if (timespan > 1000000) {
			collisions_per_sec = (collision_count * 1000000) / (double) timespan;
			if (collisions_per_sec > 0.5 && collisions_per_sec <= 2.2) {
				collision_measurement_start = swtimer_now();
				collision_state = COLLISION_STATE_KEEP;
			} else if (collisions_per_sec > 2.2) {
				collision_measurement_start = swtimer_now();
				collision_state = COLLISION_STATE_KEEP;
			} else {
				collision_state = COLLISION_STATE_INITIAL;
			}
		}
	} else if (collision_state == COLLISION_STATE_KEEP) {
		uint64_t timespan = swtimer_now() - collision_measurement_start;
		if (timespan > 5000000) {
			collision_state = COLLISION_STATE_INITIAL;
		}
	}

	// Adjust initial window size according to collision rate
	if (collisions_per_sec > 0.5 && collisions_per_sec <= 2.2) {
		min_window_size *= 2;
	} else if (collisions_per_sec > 2.2) {
		min_window_size *= 4;
	}

	uint16_t windowSize = min_window_size;		// Start with window size of PRIO_XXX_MIN_WINDOW_SIZE
	uint16_t backoff = 0;						// Backoff between 1 and windowSize
	uint32_t total;								// Holds the total wait time before send try
	uint32_t cs_timeout;						// Current carrier sense timeout value

	if (protocol == 0)
	{
		return RADIO_INVALID_PARAM;				// Not allowed, protocol id must be greater zero
	}

	cc1100_phy_mutex_lock();					// Lock radio for exclusive access

	// Get carrier sense timeout based on overall error rate till now
	send_csmaca_calls++;
	int fail_percentage = (send_csmaca_calls_cs_timeout * 100) / send_csmaca_calls;
	if (fail_percentage == 0) fail_percentage = 1;
	cs_timeout = CARRIER_SENSE_TIMEOUT / fail_percentage;
	if (cs_timeout < CARRIER_SENSE_TIMEOUT_MIN) cs_timeout = CARRIER_SENSE_TIMEOUT_MIN;

	cc1100_cs_init();							// Initialize carrier sensing

	window:
		if (backoff != 0) goto cycle;			// If backoff was 0
		windowSize *= 2;						// ...double the current window size
		if (windowSize > max_window_size)
		{
			windowSize = max_window_size;		// This is the maximum size allowed
		}
		backoff = rand() % windowSize;			// ...and choose new backoff
		if (backoff < 0) backoff *= -1;
		backoff += (uint16_t) 1;
	cycle:
		cs_timeout_flag = 0;					// Carrier sense timeout flag
		cs_hwtimer_id = hwtimer_set(cs_timeout,	// Set hwtimer to set CS timeout flag
				cs_timeout_cb, NULL);
		while (cc1100_cs_read())				// Wait until air is free
		{
			if (cs_timeout_flag)
			{
				send_csmaca_calls_cs_timeout++;
#ifndef CSMACA_MAC_AGGRESSIVE_MODE
				cc1100_phy_mutex_unlock();
				cc1100_go_after_tx();			// Go from RX to default mode
				return RADIO_CS_TIMEOUT;		// Return immediately
#endif
#ifdef CSMACA_MAC_AGGRESSIVE_MODE
				goto send;						// Send anyway
#endif
			}
		}
		hwtimer_remove(cs_hwtimer_id);			// Remove hwtimer
		cc1100_cs_write_cca(1);					// Air is free now
		cc1100_cs_set_enabled(true);
		if (cc1100_cs_read()) goto window;		// GDO0 triggers on rising edge, so
												// test once after interrupt is enabled
		if (backoff > 0) backoff--;				// Decrement backoff counter
		total = slottime;						// Calculate total wait time
		total *= (uint32_t)backoff;				// Slot vector set
		total += difs;							// ...and standard DIFS wait time
		cs_timeout_flag = 0;					// Carrier sense timeout flag
		cs_hwtimer_id = hwtimer_set(total,		// Set hwtimer to set CS timeout flag
				cs_timeout_cb, NULL);
		while (!cs_timeout_flag
				|| !cc1100_cs_read_cca())		// Wait until timeout is finished
		{
			if (cc1100_cs_read_cca() == 0)		// Is the air still free?
			{
				hwtimer_remove(cs_hwtimer_id);
				goto window;					// No. Go back to new wait period.
			}
		}
		cc1100_cs_set_enabled(false);
#ifdef CSMACA_MAC_AGGRESSIVE_MODE
	send:
#endif
		int res = cc1100_send(address, protocol, priority, payload, payload_len);
		if (res < 0) {
			collision_count++;
		}
		return res;
}