From c38fcd7a5ff288502927cd8b5ddde37f7d7e5438 Mon Sep 17 00:00:00 2001
From: asterix <asterix@38d2e660-2303-0410-9eaa-f027e97ec537>
Date: Fri, 15 Oct 2010 13:32:09 +0000
Subject: [PATCH] Add entropy generation for stm32.

git-svn-id: https://src.develer.com/svnoss/bertos/trunk@4430 38d2e660-2303-0410-9eaa-f027e97ec537
---
 bertos/sec/random_stm32.c | 109 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 bertos/sec/random_stm32.c

diff --git a/bertos/sec/random_stm32.c b/bertos/sec/random_stm32.c
new file mode 100644
index 00000000..d321ef0b
--- /dev/null
+++ b/bertos/sec/random_stm32.c
@@ -0,0 +1,109 @@
+/**
+ * \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 STM32 backend implementation entropy pulling.
+ * \author Daniele Basile <asterix@develer.com>
+ *
+ */
+
+#include "random_p.h"
+
+#include <cpu/power.h>
+
+#include <drv/clock_cm3.h>
+
+#include <io/cm3.h>
+
+struct stm32_adc *adc = (struct stm32_adc *)ADC1_BASE;
+
+/*
+ * Return the cpu core temperature in raw format
+ */
+INLINE uint16_t hw_readRawTemp(void)
+{
+	/* We sample only from one channel */
+	adc->SQR1 |= BV(SQR1_SQ_LEN_SHIFT);
+	adc->SQR3 = (ADC_TEMP_CH & SQR3_SQ_MASK);
+
+	/* Start convertion */
+	adc->CR2 |= CR2_EXTTRIG_SWSTRT_SET;
+
+	/* Wait in polling until conversion is done */
+	while (!(adc->SR & BV(SR_EOC)))
+		cpu_relax();
+
+	/* Return the last converted data */
+    return (uint16_t)adc->DR;
+}
+
+INLINE void hw_initIntTemp(void)
+{
+	RCC->APB2ENR |= RCC_APB2_ADC1;
+
+	/* Reset registry */
+	adc->CR1 = 0;
+	adc->CR2 = 0;
+	adc->SQR1 = 0;
+	adc->SQR2 = 0;
+	adc->SQR3 = 0;
+
+	/*
+	 * Configure ADC
+	 *  - Regular mode
+	 *  - Wake up adc
+	 *  - Wake up temperature and Vrefint
+	 */
+	adc->CR2 |= BV(CR2_ADON) | ADC_EXTERNALTRIGCONV_NONE | BV(CR2_TSVREFE);
+
+	/* Set 17.1usec sampling time*/
+	adc->SMPR1 |= ((ADC_SAMPLETIME_239CYCLES5 << SMPR1_CH17) | (ADC_SAMPLETIME_239CYCLES5 << SMPR1_CH16));
+}
+
+
+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;
+	}
+}
-- 
2.25.1