contiki/cpu/cc2430/dev/random.c

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2012-03-05 16:28:06 +00:00
/*
* Copyright (c) 2010, Loughborough University - 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.
*/
/**
* \file
* Random number generator routines exploiting the cc2430 hardware
* capabilities.
*
* This file overrides core/lib/random.c.
*
* \author
* George Oikonomou - <oikonomou@users.sourceforge.net>
*/
#include "cc2430_sfr.h"
#include "dev/cc2430_rf.h"
/*---------------------------------------------------------------------------*/
/**
* \brief Generates a new random number using the cc2430 RNG.
* \return The random number.
*/
unsigned short
random_rand(void)
{
/* Clock the RNG LSFR once */
ADCCON1 |= ADRCTRL0;
return (RNDL | (RNDH << 8));
}
/*---------------------------------------------------------------------------*/
/**
* \brief Seed the cc2430 random number generator.
* \param seed Seed value for the RNG.
*
* If the SEED argument is 0, seed the RNG with IF_ADC as
* discussed in the cc2430 datasheet (rev. 2.1), section 13.11.2.2,
* page 134. Seeding with this method should not be done during
* normal radio operation. Thus, use this function before
* initialising the network.
*
* If the SEED is provided, seed with this value instead. This will
* result in the same sequence of random numbers each time the node
* reboots. So, don't use it unless you have a reason (e.g. tests)
*/
void
random_init(unsigned short seed)
{
int i;
/* Comment out this if() block to save a nice 16 bytes of code size */
if(seed) {
/* If the caller provides a seed, write the high-byte first and then
* write the low byte */
RNDL = seed >> 8; /* High byte first */
RNDL = seed & 0xFF;
return;
}
/*
* cc2430 Datasheet:
* "When a true random value is required, the LFSR should be seeded by
* writing RNDL with random values from the IF_ADC in the RF receive path."
*
* "To use this seeding method, the radio must first be powered on by
* enabling the voltage regulator"
*/
RFPWR &= ~RREG_RADIO_PD; /* Turn on the voltage regulator */
while(!(RFIF & IRQ_RREG_ON)); /* Wait for power up*/
/* OK, it's powered. The respective interrupt flag has been set, clear it */
RFIF &= ~IRQ_RREG_ON;
/*
* "The radio should be placed in infinite TX state, to avoid possible sync
* detect in RX state."
*
* Judging by old chipcon cc2430 code examples as well as by the way cc2530
* works, this is very likely to be "RX state" (i.e. a typo in the datasheet)
*
* With infinite TX, ADCTSTx always read as 0 so we'll use infinite RX
*/
MDMCTRL1L = 0x02; /* RX mode 10 - RX_INFINITE state */
/* "Enter RX State - Immediate" command strobe */
cc2430_rf_command(ISRXON);
/* Make sure the RNG is on */
ADCCON1 &= ~(ADRCTRL1 | ADRCTRL0);
/* Wait for IF_ADC I-branch and Q-branch values */
while(!(ADCTSTH & ADCTSTL));
/* 32 times as per the chipcon example. This seems to increase randomness */
for(i = 0; i < 32; i++) {
/* Seed the RNG by writing into RNDL twice with values from ADCTSTx */
RNDL = ADCTSTH;
RNDL = ADCTSTL;
/* Clock the RNG LSFR once */
ADCCON1 |= ADRCTRL0;
}
/*
* Exit RX state. Just shut down, network initialisation will take care of
* properly starting the radio for us.
*/
RFPWR |= RREG_RADIO_PD;
}