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// #################################################################################################
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// # << NEORV32: neorv32_trng.c - True Random Number Generator (TRNG) HW Driver >> #
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// # ********************************************************************************************* #
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// # BSD 3-Clause License #
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// # #
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// # Copyright (c) 2020, Stephan Nolting. All rights reserved. #
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// # #
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// # Redistribution and use in source and binary forms, with or without modification, are #
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// # permitted provided that the following conditions are met: #
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// # #
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// # 1. Redistributions of source code must retain the above copyright notice, this list of #
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// # conditions and the following disclaimer. #
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// # #
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// # 2. Redistributions in binary form must reproduce the above copyright notice, this list of #
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// # conditions and the following disclaimer in the documentation and/or other materials #
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// # provided with the distribution. #
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// # #
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// # 3. Neither the name of the copyright holder nor the names of its contributors may be used to #
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// # endorse or promote products derived from this software without specific prior written #
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// # permission. #
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// # #
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// # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS #
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// # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF #
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// # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE #
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// # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, #
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// # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE #
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// # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED #
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// # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING #
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// # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED #
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// # OF THE POSSIBILITY OF SUCH DAMAGE. #
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// # ********************************************************************************************* #
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// # The NEORV32 Processor - https://github.com/stnolting/neorv32 (c) Stephan Nolting #
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// #################################################################################################
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/**********************************************************************//**
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* @file neorv32_trng.c
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* @author Stephan Nolting
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* @brief True Random Number Generator (TRNG) HW driver source file.
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*
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* @note These functions should only be used if the TRNG unit was synthesized (IO_TRNG_USE = true).
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**************************************************************************/
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#include "neorv32.h"
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#include "neorv32_trng.h"
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/**********************************************************************//**
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* Check if TRNG unit was synthesized.
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*
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* @return 0 if TRNG was not synthesized, 1 if TRNG is available.
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**************************************************************************/
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int neorv32_trng_available(void) {
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if (neorv32_cpu_csr_read(CSR_MFEATURES) & (1 << CPU_MFEATURES_IO_TRNG)) {
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return 1;
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}
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else {
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return 0;
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}
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}
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/**********************************************************************//**
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* Enable and configure true random number generator. The TRNG control register bits are listed in #NEORV32_TRNG_CT_enum.
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*
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* @param[in] tap_mask 16-bit tap mask for GARO array.
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* @return Returns 0 if the provided tap_mask works correctly (GARO-array is oscillating), returns 1 otherwise.
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**************************************************************************/
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int neorv32_trng_setup(uint16_t tap_mask) {
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TRNG_CT = 0; // reset
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// configure
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uint32_t tap_config = (uint32_t)(tap_mask);
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tap_config = tap_config << TRNG_CT_TAP_LSB;
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TRNG_CT = (1 << TRNG_CT_EN) | tap_config;
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neorv32_cpu_delay_ms(1);
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// check if TRNG is oscillating
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uint16_t trng_data;
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if (neorv32_trng_get(&trng_data) == 0) {
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return 0;
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}
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else {
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return 1;
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}
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}
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/**********************************************************************//**
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* Disable true random number generator.
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**************************************************************************/
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void neorv32_trng_disable(void) {
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TRNG_CT &= ~((uint32_t)(1 << TRNG_CT_EN));
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}
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/**********************************************************************//**
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* Get random data from TRNG.
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*
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* @param[in,out] data uint16_t pointer for storing random data word
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* @return Valid data when 0, invalid data when 1
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**************************************************************************/
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int neorv32_trng_get(uint16_t *data) {
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int i;
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const int max_try = 16;
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uint32_t trng_data;
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uint32_t rnd_data;
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for(i=0; i<max_try; i++) {
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trng_data = TRNG_DATA;
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rnd_data = trng_data >> TRNG_DATA_LSB;
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*data = (uint16_t)rnd_data;
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if (trng_data & (1<<TRNG_DATA_VALID)) { // output data valid?
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return 0; // valid
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}
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}
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return 1; // invalid
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}
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/**********************************************************************//**
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* Try to find a valid TRNG tap configuration mask.
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*
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* @return Tap mask for configuring the TRNG. If return is zero, no valid tap mask was found.
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**************************************************************************/
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uint16_t neorv32_trng_find_tap_mask(void) {
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int j;
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uint16_t tap_config16 = 0xfff0; // keep the lowest inverters without feedback
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uint16_t trng_data;
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int success = 0;
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// tap mask is zero, try to find a nice one
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while (1) {
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// good mask found?
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if ((success) || (tap_config16 <= 0x0008)) {
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break;
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}
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// generate a new tap
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tap_config16 -= 0x0008;
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// install it
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if (neorv32_trng_setup(tap_config16)) {
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continue;
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}
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// does it work?
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success = 1;
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for (j=0; j < 100; j++) {
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neorv32_cpu_delay_ms(1);
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if (neorv32_trng_get(&trng_data)) { // stop testing on fail
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success = 0;
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break;
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}
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}
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}
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return (uint16_t)tap_config16;
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}
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