94 lines
2.9 KiB
C
94 lines
2.9 KiB
C
/**
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* \file
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* <!--
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* This file is part of BeRTOS.
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*
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* Bertos is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*
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* As a special exception, you may use this file as part of a free software
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* library without restriction. Specifically, if other files instantiate
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* templates or use macros or inline functions from this file, or you compile
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* this file and link it with other files to produce an executable, this
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* file does not by itself cause the resulting executable to be covered by
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* the GNU General Public License. This exception does not however
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* invalidate any other reasons why the executable file might be covered by
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* the GNU General Public License.
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*
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* Copyright 2010 Develer S.r.l. (http://www.develer.com/)
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*
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* -->
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*
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* \brief LM3 backend implementation entropy pulling.
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* \author Giovanni Bajo <rasky@develer.com>
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*/
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#include "random_p.h"
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#include <cpu/power.h>
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#include <io/cm3.h>
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#include <drv/clock_cm3.h>
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/*
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* Return the cpu core temperature in raw format
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*/
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INLINE uint16_t hw_readRawTemp(void)
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{
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/* Trig the temperature sampling */
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HWREG(ADC0_BASE + ADC_O_PSSI) |= ADC_PSSI_SS3;
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while (!(HWREG(ADC0_BASE + ADC_O_SSFSTAT3) & ADC_SSFSTAT3_FULL))
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cpu_relax();
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return (uint16_t)HWREG(ADC0_BASE + ADC_O_SSFIFO3);
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}
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INLINE void hw_initIntTemp(void)
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{
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SYSCTL_RCGC0_R |= SYSCTL_RCGC0_ADC0;
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lm3s_busyWait(10);
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/* Disable all sequence */
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HWREG(ADC0_BASE + ADC_O_ACTSS) = 0;
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/* Set trigger event to programmed (for all sequence) */
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HWREG(ADC0_BASE + ADC_O_EMUX) = 0;
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/* Enalbe read of temperature sensor */
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HWREG(ADC0_BASE + ADC_O_SSCTL3) |= ADC_SSCTL3_TS0;
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/* Enable sequence S03 (single sample on select channel) */
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HWREG(ADC0_BASE + ADC_O_ACTSS) |= ADC_ACTSS_ASEN3;
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}
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void random_pull_entropy(uint8_t *entropy, size_t len)
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{
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// We use the internal temperature sensor of LM3S as a source of entropy.
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// The last bit of the acquisition is very variable and with a decent distribution
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// to consider it "entropic". It does not really matter because it will
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// go through a randomness extractor anyway.
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hw_initIntTemp();
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for (size_t j=0; j<len; j++)
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{
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uint8_t accum = 0;
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for (int b=0; b<8; ++b)
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if (hw_readRawTemp() & 1)
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accum |= 1<<b;
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*entropy++ = accum;
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}
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}
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