elec0017_project/rng.c

// Based on https://github.com/manitou48/CC3200/blob/master/rng.ino
//#include <rng.h>

#include "rng.h"
#include <stdint.h>
#include <Energia.h>

#include <driverlib/prcm.h>
#include <driverlib/systick.h>

#define DTICKS 200
#define gWDT_buffer_SIZE 32
#define WDT_POOL_SIZE 8

//const uint8_t gWDT_buffer_SIZE=32;
//const uint8_t WDT_POOL_SIZE=8;

uint8_t gWDT_buffer[gWDT_buffer_SIZE];
uint8_t gWDT_buffer_position;
uint8_t gWDT_loop_counter;
volatile uint8_t gWDT_pool_start;
volatile uint8_t gWDT_pool_end;
volatile uint8_t gWDT_pool_count;
volatile uint32_t gWDT_entropy_pool[WDT_POOL_SIZE];

uint32_t random(void) {
  uint32_t retVal;
  uint8_t waiting;
  while (gWDT_pool_count < 1) waiting += 1;
  noInterrupts();  // crtical section
    retVal = gWDT_entropy_pool[gWDT_pool_start];
    gWDT_pool_start = (gWDT_pool_start + 1) % WDT_POOL_SIZE;
    --gWDT_pool_count;
  interrupts();
  return(retVal);
}

void tick(void) {
  long long t = PRCMSlowClkCtrGet();
  PRCMSlowClkCtrMatchSet(t + DTICKS); // next interrupt time
  PRCMIntStatus(); // clear

  gWDT_buffer[gWDT_buffer_position] = SysTickValueGet();
  gWDT_buffer_position++;                     // every time the WDT interrupt is triggered
  if (gWDT_buffer_position >= gWDT_buffer_SIZE)
  {
    gWDT_pool_end = (gWDT_pool_start + gWDT_pool_count) % WDT_POOL_SIZE;
    // The following code is an implementation of Jenkin's one at a time hash
    // This hash function has had preliminary testing to verify that it
    // produces reasonably uniform random results when using WDT jitter
    // on a variety of Arduino platforms
    for(gWDT_loop_counter = 0; gWDT_loop_counter < gWDT_buffer_SIZE; ++gWDT_loop_counter)
      {
    gWDT_entropy_pool[gWDT_pool_end] += gWDT_buffer[gWDT_loop_counter];
    gWDT_entropy_pool[gWDT_pool_end] += (gWDT_entropy_pool[gWDT_pool_end] << 10);
    gWDT_entropy_pool[gWDT_pool_end] ^= (gWDT_entropy_pool[gWDT_pool_end] >> 6);
      }
    gWDT_entropy_pool[gWDT_pool_end] += (gWDT_entropy_pool[gWDT_pool_end] << 3);
    gWDT_entropy_pool[gWDT_pool_end] ^= (gWDT_entropy_pool[gWDT_pool_end] >> 11);
    gWDT_entropy_pool[gWDT_pool_end] += (gWDT_entropy_pool[gWDT_pool_end] << 15);
    gWDT_entropy_pool[gWDT_pool_end] = gWDT_entropy_pool[gWDT_pool_end];
    gWDT_buffer_position = 0; // Start collecting the next 32 bytes of Timer 1 counts
    if (gWDT_pool_count == WDT_POOL_SIZE) // The entropy pool is full
      gWDT_pool_start = (gWDT_pool_start + 1) % WDT_POOL_SIZE;
    else // Add another unsigned long (32 bits) to the entropy pool
      ++gWDT_pool_count;
  }
}

void RNGSetup(void) {
    long t = PRCMSlowClkCtrGet();
    PRCMSlowClkCtrMatchSet(t + DTICKS); // next interrupt time
    PRCMIntRegister(tick);
    PRCMIntEnable(PRCM_INT_SLOW_CLK_CTR);
    gWDT_buffer_position=0;
    gWDT_pool_start = 0;
    gWDT_pool_end = 0;
    gWDT_pool_count = 0;
}