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

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

// # ********************************************************************************************* #

// # 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 0 if execution was successful

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

int main(void) {

  // check if UART unit is implemented at all

  if (neorv32_uart0_available() == 0) {

    return 1;

  }

  // 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_uart0_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_uart0_printf("\n<<< NEORV32 TRNG Demo >>>\n");

  // check if TRNG unit is implemented at all

  if (neorv32_trng_available() == 0) {

    neorv32_uart0_printf("No TRNG implemented.");

    return 1;

  }

  // enable TRNG

  neorv32_trng_enable();

  neorv32_cpu_delay_ms(100); // TRNG "warm up"

  while(1) {

    // main menu

    neorv32_uart0_printf("\nCommands:\n"

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

                         " h: Generate histogram and analyze data\n");

    neorv32_uart0_printf("CMD:> ");

    char cmd = neorv32_uart0_getc();

    neorv32_uart0_putc(cmd); // echo

    neorv32_uart0_printf("\n");

    if (cmd == 'n') {

      print_random_data();

    }

    else if (cmd == 'h') {

      generate_histogram();

    }

    else {

      neorv32_uart0_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_uart0_printf("\nTRNG error!\n");

      break;

    }

    neorv32_uart0_printf("%u ", (uint32_t)(trng_data));

    num_samples++;

    if (neorv32_uart0_char_received()) { // abort when key pressed

      break;

    }

  }

  neorv32_uart0_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;

  uint8_t trng_data;

  uint64_t average = 0;

  neorv32_uart0_printf("Press any key to start.\n");

  while(neorv32_uart0_char_received() == 0);

  neorv32_uart0_printf("Sampling... Press any key to stop.\n");

  // clear histogram

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

    hist[i] = 0;

  }

  // sample random data

  while(1) {

    // get raw TRNG data

    if (neorv32_trng_get(&trng_data)) {

      continue;

    }

    // add to histogram

    hist[trng_data & 0xff]++;

    cnt++;

    // average

    average += (uint64_t)trng_data;

    // abort conditions

    if ((neorv32_uart0_char_received()) || // abort when key pressed

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

      break;

    }

  }

  average = average / cnt;

  // deviation (histogram samples)

  uint32_t avg_occurence = cnt / 256;

  int32_t tmp_int;

  int32_t dev_int;

  int32_t dev_int_max = 0x80000000UL; uint32_t bin_max = 0;

  int32_t dev_int_min = 0x7fffffffUL; uint32_t bin_min = 0;

  int32_t dev_int_avg = 0;

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

    tmp_int = (int32_t)hist[i];

    dev_int = tmp_int - avg_occurence;

    dev_int_avg += (uint64_t)dev_int;

    if (dev_int < dev_int_min) {

      dev_int_min = dev_int;

      bin_min = i;

    }

    if (dev_int > dev_int_max) {

      dev_int_max = dev_int;

      bin_max = i;

    }

  }

  dev_int_avg = dev_int_avg / 256;

  // print histogram

  neorv32_uart0_printf("Histogram [random data value] : [# occurrences]\n");

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

    neorv32_uart0_printf("%u: %u\n", (uint32_t)i, hist[i]);

  }

  neorv32_uart0_printf("\n");

  // print results

  neorv32_uart0_printf("Analysis results (integer only)\n\n");

  neorv32_uart0_printf("Number of samples: %u\n", cnt);

  neorv32_uart0_printf("Arithmetic mean:   %u\n", (uint32_t)average);

  neorv32_uart0_printf("\nArithmetic deviation\n");

  neorv32_uart0_printf("Avg. occurrence: %u\n", avg_occurence);

  neorv32_uart0_printf("Avg. deviation:  %i\n", dev_int_avg);

  neorv32_uart0_printf("Minimum:         %i (histogram bin %u)\n", dev_int_min, bin_min);

  neorv32_uart0_printf("Maximum:         %i (histogram bin %u)\n", dev_int_max, bin_max);

}