SEC: Add LM3S backend for entropy pulling.

git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4338 38d2e660-2303-0410-9eaa-f027e97ec537

diff --git a/bertos/sec/random_lm3s.c b/bertos/sec/random_lm3s.c
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+++ b/bertos/sec/random_lm3s.c
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+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos 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 Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2010 Develer S.r.l. (http://www.develer.com/)
+ *
+ * -->
+ *
+ * \brief LM3 backend implementation entropy pulling.
+ * \author Giovanni Bajo <rasky@develer.com>
+ *
+ */
+
+#include "random_p.h"
+#include <io/cm3.h>
+#include <drv/clock_lm3s.h>
+
+/*
+ * Return the cpu core temperature in raw format
+ */
+INLINE uint16_t hw_readRawTemp(void)
+{
+    /* Trig the temperature sampling */
+    HWREG(ADC0_BASE + ADC_O_PSSI) |= ADC_PSSI_SS3;
+
+       while (!(HWREG(ADC0_BASE + ADC_O_SSFSTAT3) & ADC_SSFSTAT3_FULL));
+
+    return (uint16_t)HWREG(ADC0_BASE + ADC_O_SSFIFO3);
+}
+
+INLINE void hw_initIntTemp(void)
+{
+    SYSCTL_RCGC0_R |= SYSCTL_RCGC0_ADC0;
+
+       lm3s_busyWait(10);
+
+    /* Disable all sequence */
+    HWREG(ADC0_BASE + ADC_O_ACTSS) = 0;
+    /* Set trigger event to programmed (for all sequence) */
+    HWREG(ADC0_BASE + ADC_O_EMUX) = 0;
+    /* Enalbe read of temperature sensor */
+    HWREG(ADC0_BASE + ADC_O_SSCTL3) |= ADC_SSCTL3_TS0;
+    /* Enable sequence S03 (single sample on select channel) */
+    HWREG(ADC0_BASE + ADC_O_ACTSS) |= ADC_ACTSS_ASEN3;
+}
+
+
+void random_pull_entropy(uint8_t *entropy, size_t len)
+{
+       // We use the internal temperature sensor of LM3S as a source of entropy.
+       // The last bit of the acquisition is very variable and with a decent distribution
+       // to consider it "entropic". It does not really matter because it will
+       // go through a randomness extractor anyway.
+       hw_initIntTemp();
+       
+       for (size_t j=0; j<len; j++)
+       {
+               uint8_t accum = 0;
+               for (int b=0; b<8; ++b)
+                       if (hw_readRawTemp() & 1)
+                               accum |= 1<<b;
+               
+               *entropy++ = accum;
+       }
+}