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// # << NEORV32 - TRNG Demo Program >>                                                             #

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// # BSD 3-Clause License                                                                          #

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// # Copyright (c) 2021, Stephan Nolting. All rights reserved.                                     #

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// # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

// #################################################################################################

/**********************************************************************//**

 * @file demo_trng/main.c

 * @author Stephan Nolting

 * @brief True random number generator demo program.

 **************************************************************************/

#include <neorv32.h>

/**********************************************************************//**

 * @name User configuration

 **************************************************************************/

/**@{*/

/** UART BAUD rate */

#define BAUD_RATE 19200

/**@}*/

// prototypes

void print_random_data(void);

void generate_histogram(void);

/**********************************************************************//**

 * Simple true random number test/demo program.

 *

 * @note This program requires the UART and the TRNG to be synthesized.

 *

 * @return Irrelevant.

 **************************************************************************/

int main(void) {

  // check if UART unit is implemented at all

  if (neorv32_uart_available() == 0) {

    return 0;

  }

  // capture all exceptions and give debug info via UART

  // this is not required, but keeps us safe

  neorv32_rte_setup();

  // init UART at default baud rate, no parity bits, ho hw flow control

  neorv32_uart_setup(BAUD_RATE, PARITY_NONE, FLOW_CONTROL_NONE);

  // check available hardware extensions and compare with compiler flags

  neorv32_rte_check_isa(0); // silent = 0 -> show message if isa mismatch

  // intro

  neorv32_uart_printf("\n--- TRNG Demo ---\n\n");

  // check if TRNG unit is implemented at all

  if (neorv32_trng_available() == 0) {

    neorv32_uart_printf("No TRNG implemented.");

    return 0;

  }

  // enable TRNG

  neorv32_trng_enable();

  while(1) {

    // main menu

    neorv32_uart_printf("\nCommands:\n"

                        " n: Print 8-bit random numbers (abort by pressing any key)\n"

                        " h: Generate and print histogram\n");

    neorv32_uart_printf("CMD:> ");

    char cmd = neorv32_uart_getc();

    neorv32_uart_putc(cmd); // echo

    neorv32_uart_printf("\n");

    if (cmd == 'n') {

      print_random_data();

    }

    else if (cmd == 'h') {

      generate_histogram();

    }

    else {

      neorv32_uart_printf("Invalid command.\n");

    }

  }

  return 0;

}

/**********************************************************************//**

 * Print random numbers until a key is pressed.

 **************************************************************************/

void print_random_data(void) {

  uint32_t num_samples = 0;

  int err = 0;

  uint8_t trng_data;

  while(1) {

    err = neorv32_trng_get(&trng_data);

    if (err) {

      neorv32_uart_printf("\nTRNG error!\n");

      break;

    }

    neorv32_uart_printf("%u ", (uint32_t)(trng_data));

    num_samples++;

    if (neorv32_uart_char_received()) { // abort when key pressed

      break;

    }

  }

  neorv32_uart_printf("\nPrinted samples: %u\n", num_samples);

}

/**********************************************************************//**

 * Generate and print histogram. Samples random data until a key is pressed.

 **************************************************************************/

void generate_histogram(void) {

  uint32_t hist[256];

  uint32_t i;

  uint32_t cnt = 0;

  int err = 0;

  uint8_t trng_data;

  neorv32_uart_printf("Press any key to start.\n");

  while(neorv32_uart_char_received() == 0);

  neorv32_uart_printf("Sampling... Press any key to stop.\n");

  // clear histogram

  for (i=0; i<256; i++) {

    hist[i] = 0;

  }

  // sample random data

  while(1) {

    err = neorv32_trng_get(&trng_data);

    hist[trng_data & 0xff]++;

    cnt++;

    if (err) {

      neorv32_uart_printf("\nTRNG error!\n");

      break;

    }

    if (neorv32_uart_char_received()) { // abort when key pressed

      break;

    }

    if (cnt & 0x80000000UL) { // to prevent overflow

      break;

    }

  }

  // print histogram

  neorv32_uart_printf("Histogram [random data value] : [# occurences]\n");

  for (i=0; i<256; i++) {

    neorv32_uart_printf("%u: %u\n", (uint32_t)i, hist[i]);

  }

  neorv32_uart_printf("\nSamples: %u\n", cnt);

  // average

  uint64_t average = 0;

  for (i=0; i<256; i++) {

    average += (uint64_t)hist[i] * i;

  }

  average = average / ((uint64_t)cnt);

  neorv32_uart_printf("Average value: %u\n", (uint32_t)average);

}