Subversion Repositories neorv32

// #################################################################################################
// # << NEORV32: neorv32_trng.c - True Random Number Generator (TRNG) HW Driver >>                 #
// # ********************************************************************************************* #
// # BSD 3-Clause License                                                                          #
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// # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #
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// # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #
// #################################################################################################
 
 
/**********************************************************************//**
 * @file neorv32_trng.c
 * @author Stephan Nolting
 * @brief True Random Number Generator (TRNG) HW driver source file.
 *
 * @note These functions should only be used if the TRNG unit was synthesized (IO_TRNG_USE = true).
 **************************************************************************/
 
#include "neorv32.h"
#include "neorv32_trng.h"
 
 
/**********************************************************************//**
 * Check if TRNG unit was synthesized.
 *
 * @return 0 if TRNG was not synthesized, 1 if TRNG is available.
 **************************************************************************/
int neorv32_trng_available(void) {
 
  if (neorv32_cpu_csr_read(CSR_MFEATURES) & (1 << CPU_MFEATURES_IO_TRNG)) {
    return 1;
  }
  else {
    return 0;
  }
}
 
 
/**********************************************************************//**
 * Enable and configure true random number generator. The TRNG control register bits are listed in #NEORV32_TRNG_CT_enum.
 *
 * @param[in] tap_mask 16-bit tap mask for GARO array.
 * @return Returns 0 if the provided tap_mask works correctly (GARO-array is oscillating), returns 1 otherwise.
 **************************************************************************/
int neorv32_trng_setup(uint16_t tap_mask) {
 
  TRNG_CT = 0; // reset
 
  // configure
  uint32_t tap_config = (uint32_t)(tap_mask);
  tap_config = tap_config << TRNG_CT_TAP_LSB;
  TRNG_CT = (1 << TRNG_CT_EN) | tap_config;
 
  neorv32_cpu_delay_ms(1);
 
  // check if TRNG is oscillating
  uint16_t trng_data;
  if (neorv32_trng_get(&trng_data) == 0) {
    return 0;
  }
  else {
    return 1;
  }
}
 
 
/**********************************************************************//**
 * Disable true random number generator.
 **************************************************************************/
void neorv32_trng_disable(void) {
 
  TRNG_CT &= ~((uint32_t)(1 << TRNG_CT_EN));
}
 
 
/**********************************************************************//**
 * Get random data from TRNG.
 *
 * @param[in,out] data uint16_t pointer for storing random data word
 * @return Valid data when 0, invalid data when 1
 **************************************************************************/
int neorv32_trng_get(uint16_t *data) {
 
  int i;
  const int max_try = 16;
  uint32_t trng_data;
  uint32_t rnd_data;
 
  for(i=0; i<max_try; i++) {
 
    trng_data = TRNG_DATA;
    rnd_data  = trng_data >> TRNG_DATA_LSB;
    *data = (uint16_t)rnd_data;
 
    if (trng_data & (1<<TRNG_DATA_VALID)) { // output data valid?
      return 0; // valid
    }
 
  }
 
  return 1; // invalid
}
 
 
/**********************************************************************//**
 * Try to find a valid TRNG tap configuration mask.
 *
 * @return Tap mask for configuring the TRNG. If return is zero, no valid tap mask was found.
 **************************************************************************/
uint16_t neorv32_trng_find_tap_mask(void) {
 
  int j;
  uint16_t tap_config16 = 0xfff0; // keep the lowest inverters without feedback
  uint16_t trng_data;
  int success = 0;
 
  // tap mask is zero, try to find a nice one
  while (1) {
 
    // good mask found?
    if ((success) || (tap_config16 <= 0x0008)) {
      break;
    }
 
    // generate a new tap
    tap_config16 -= 0x0008;
 
    // install it
    if (neorv32_trng_setup(tap_config16)) {
      continue;
    }
 
    // does it work?
    success = 1;
    for (j=0; j < 100; j++) {
      neorv32_cpu_delay_ms(1);
      if (neorv32_trng_get(&trng_data)) { // stop testing on fail
        success = 0;
        break;
      }
    }
  }
 
  return (uint16_t)tap_config16;
}