wandrson · February 2, 2024 05:37 · Apr 11, 2014 · Apr 8, 2014 · Apr 6, 2014 · Apr 6, 2014
diff --git a/TrueRandomSeed.ino b/TrueRandomSeed.ino
@@ -1,58 +1,70 @@
 // TrueRandomSeed.ino
-//   This example sketch shows how to provide a truly random seed value to the built in library pseudo random number generator.  This ensures that your
-//   sketch will be using a different sequence of random numbers every time it runs.  Unlike the usually suggested randomSeed(analogRead(0)) this method
-//   will provide a much more uniform and varied seed value.  For more information about the basic technique used here to produce a random number or if
-//   you need more than one such number you can find a library, Entropy from the following web site along with documentation of how the library has been
-//   tested to provide TRUE random numbers on a variety of AVR chips and arduino environments.
-//     http://code.google.com/p/avr-hardware-random-number-generation/wiki/WikiAVRentropy
+// This example sketch shows how to provide a truly random seed value to the built in
+// library pseudo random number generator. This ensures that your sketch will be
+// using a different sequence of random numbers every time it runs. Unlike the
+// usually suggested randomSeed(analogRead(0)) this method will provide a much more
+// uniform and varied seed value. For more information about the basic technique used
+// here to produce a random number or if you need more than one such number you can
+// find a library, Entropy from the following web site along with documentation of how
+// the library has been tested to provide TRUE random numbers on a variety of AVR
+// chips and arduino environments.
 //
-//   Copyright 2014 by Walter Anderson, wandrson01 at gmail dot com
+// https://sites.google.com/site/astudyofentropy/project-definition/
+// timer-jitter-entropy-sources/entropy-library
 //
-
+// Copyright 2014 by Walter Anderson, wandrson01 at gmail dot com
+//
+
 #include <avr/interrupt.h>
 #include <avr/wdt.h>
 #include <util/atomic.h>
-// The following addresses a problem in version 1.0.5 and earlier of the Arduino IDE that prevents randomSeed from working
-// properly. https://github.com/arduino/Arduino/issues/575
+// The following addresses a problem in version 1.0.5 and earlier of the Arduino IDE
+// that prevents randomSeed from working properly.
+// https://github.com/arduino/Arduino/issues/575
 #define randomSeed(s) srandom(s)
-
-volatile uint32_t seed;                              // These two variables can be reused in your program after the function CreateTrulyRandomSeed()
-volatile int8_t nrot;                               // executes in the setup() function.
-
+
+volatile uint32_t seed; // These two variables can be reused in your program after the
+volatile int8_t nrot; // function CreateTrulyRandomSeed()executes in the setup()
+                     // function.
+
 void CreateTrulyRandomSeed()
 {
-  seed = 0;
-  nrot = 32;                                         // Must be at least 4, but more increased the uniformity of the produced seeds entropy.
-  cli();                                             // Temporarily turn off interrupts, until WDT interrupt turned on
-  MCUSR = 0;                                         // Use the MCU status register to reset flags for WDR, BOR, EXTR, and POWR
-  _WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (1<<WDE); // WDT control register, This sets the Watchdog Change Enable (WDCE) flag, which is  needed to set the 
-  _WD_CONTROL_REG = (1<<WDIE);                       // Watchdog system reset (WDE) enable and the Watchdog interrupt enable (WDIE)
-  sei();                                             // Turn interupts on
-
-  while (nrot > 0);                                  // wait here until seed is created
-
-  cli();                                             // Temporarily turn off interrupts, until WDT interrupt turned off
-  MCUSR = 0;                                         // Use the MCU status register to reset flags for WDR, BOR, EXTR, and POWR
-  _WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (0<<WDE); // WDT control register, This sets the Watchdog Change Enable (WDCE) flag, which is  needed to set the 
-  _WD_CONTROL_REG = (0<< WDIE);                       // Watchdog system reset (WDE) enable and the Watchdog interrupt enable (WDIE)
-  sei();                                             // Turn interupts on
+seed = 0;
+nrot = 32; // Must be at least 4, but more increased the uniformity of the produced
+// seeds entropy.
+// The following five lines of code turn on the watch dog timer interrupt to create
+// the seed value
+cli();
+MCUSR = 0;
+_WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (1<<WDE);
+_WD_CONTROL_REG = (1<<WDIE);
+sei();
+
+while (nrot > 0); // wait here until seed is created
+
+// The following five lines turn off the watch dog timer interrupt
+cli();
+MCUSR = 0;
+_WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (0<<WDE);
+_WD_CONTROL_REG = (0<< WDIE);
+sei();
 }
-
+ 
 ISR(WDT_vect)
 {
-  nrot--;
-  seed = seed << 8;
-  seed = seed ^ TCNT1L;
+nrot--;
+seed = seed << 8;
+seed = seed ^ TCNT1L;
 }
-
+ 
 void setup()
 {
-  CreateTrulyRandomSeed();
-  randomSeed(seed);
-  // The preceeding two function calls will take approximately 0.5 second to execute if nrot is set to 32
-  // ... the rest of your setup code should FOLLOW from here.
+CreateTrulyRandomSeed();
+randomSeed(seed);
+// The preceeding two function calls will take approximately 0.5 second to execute if
+// nrot is set to 32 ... the rest of your setup code should FOLLOW from here.
 }
-
+ 
 void loop()
 {
-}
+}
diff --git a/TrueRandomSeed.ino b/TrueRandomSeed.ino
@@ -50,6 +50,7 @@ void setup()
   CreateTrulyRandomSeed();
   randomSeed(seed);
   // The preceeding two function calls will take approximately 0.5 second to execute if nrot is set to 32
+  // ... the rest of your setup code should FOLLOW from here.
 }
 
 void loop()

diff --git a/TrueRandomSeed.ino b/TrueRandomSeed.ino
@@ -17,7 +17,7 @@
 #define randomSeed(s) srandom(s)
 
 volatile uint32_t seed;                              // These two variables can be reused in your program after the function CreateTrulyRandomSeed()
-volatile uint8_t nrot;                               // executes in the setup() function.
+volatile int8_t nrot;                               // executes in the setup() function.
 
 void CreateTrulyRandomSeed()
 {

diff --git a/TrueRandomSeed.ino b/TrueRandomSeed.ino
@@ -12,6 +12,9 @@
 #include <avr/interrupt.h>
 #include <avr/wdt.h>
 #include <util/atomic.h>
+// The following addresses a problem in version 1.0.5 and earlier of the Arduino IDE that prevents randomSeed from working
+// properly. https://github.com/arduino/Arduino/issues/575
+#define randomSeed(s) srandom(s)
 
 volatile uint32_t seed;                              // These two variables can be reused in your program after the function CreateTrulyRandomSeed()
 volatile uint8_t nrot;                               // executes in the setup() function.

diff --git a/TrueRandomSeed.ino b/TrueRandomSeed.ino
@@ -1,26 +1,38 @@
+// TrueRandomSeed.ino
+//   This example sketch shows how to provide a truly random seed value to the built in library pseudo random number generator.  This ensures that your
+//   sketch will be using a different sequence of random numbers every time it runs.  Unlike the usually suggested randomSeed(analogRead(0)) this method
+//   will provide a much more uniform and varied seed value.  For more information about the basic technique used here to produce a random number or if
+//   you need more than one such number you can find a library, Entropy from the following web site along with documentation of how the library has been
+//   tested to provide TRUE random numbers on a variety of AVR chips and arduino environments.
+//     http://code.google.com/p/avr-hardware-random-number-generation/wiki/WikiAVRentropy
 //
-// Copyright 2014 by Walter Anderson
+//   Copyright 2014 by Walter Anderson, wandrson01 at gmail dot com
 //
 
-#include <stdint.h>
 #include <avr/interrupt.h>
 #include <avr/wdt.h>
 #include <util/atomic.h>
-#include <Arduino.h>
 
-volatile uint32_t seed;
-volatile uint8_t nrot;
+volatile uint32_t seed;                              // These two variables can be reused in your program after the function CreateTrulyRandomSeed()
+volatile uint8_t nrot;                               // executes in the setup() function.
 
 void CreateTrulyRandomSeed()
 {
   seed = 0;
   nrot = 32;                                         // Must be at least 4, but more increased the uniformity of the produced seeds entropy.
-  cli();                                             // Temporarily turn off interrupts, until WDT configured
+  cli();                                             // Temporarily turn off interrupts, until WDT interrupt turned on
   MCUSR = 0;                                         // Use the MCU status register to reset flags for WDR, BOR, EXTR, and POWR
   _WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (1<<WDE); // WDT control register, This sets the Watchdog Change Enable (WDCE) flag, which is  needed to set the 
-  _WD_CONTROL_REG = _BV(WDIE);                       // Watchdog system reset (WDE) enable and the Watchdog interrupt enable (WDIE)
+  _WD_CONTROL_REG = (1<<WDIE);                       // Watchdog system reset (WDE) enable and the Watchdog interrupt enable (WDIE)
+  sei();                                             // Turn interupts on
+
+  while (nrot > 0);                                  // wait here until seed is created
+
+  cli();                                             // Temporarily turn off interrupts, until WDT interrupt turned off
+  MCUSR = 0;                                         // Use the MCU status register to reset flags for WDR, BOR, EXTR, and POWR
+  _WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (0<<WDE); // WDT control register, This sets the Watchdog Change Enable (WDCE) flag, which is  needed to set the 
+  _WD_CONTROL_REG = (0<< WDIE);                       // Watchdog system reset (WDE) enable and the Watchdog interrupt enable (WDIE)
   sei();                                             // Turn interupts on
-  while (nrot > 0);
 }
 
 ISR(WDT_vect)
@@ -32,19 +44,9 @@ ISR(WDT_vect)
 
 void setup()
 {
-  unsigned long start_time;
-  unsigned long end_time;
-  unsigned long elapsed_time;
-
-  Serial.begin(9600);
-  start_time = micros();
   CreateTrulyRandomSeed();
   randomSeed(seed);
-  end_time = micros();
-  elapsed_time = end_time - start_time;
-  Serial.print("Completed seeding the PRNG in ");
-  Serial.print(elapsed_time);
-  Serial.println(" microseconds!");
+  // The preceeding two function calls will take approximately 0.5 second to execute if nrot is set to 32
 }
 
 void loop()

diff --git a/TrueRandomSeed.ino b/TrueRandomSeed.ino
@@ -0,0 +1,52 @@
+//
+// Copyright 2014 by Walter Anderson
+//
+
+#include <stdint.h>
+#include <avr/interrupt.h>
+#include <avr/wdt.h>
+#include <util/atomic.h>
+#include <Arduino.h>
+
+volatile uint32_t seed;
+volatile uint8_t nrot;
+
+void CreateTrulyRandomSeed()
+{
+  seed = 0;
+  nrot = 32;                                         // Must be at least 4, but more increased the uniformity of the produced seeds entropy.
+  cli();                                             // Temporarily turn off interrupts, until WDT configured
+  MCUSR = 0;                                         // Use the MCU status register to reset flags for WDR, BOR, EXTR, and POWR
+  _WD_CONTROL_REG |= (1<<_WD_CHANGE_BIT) | (1<<WDE); // WDT control register, This sets the Watchdog Change Enable (WDCE) flag, which is  needed to set the 
+  _WD_CONTROL_REG = _BV(WDIE);                       // Watchdog system reset (WDE) enable and the Watchdog interrupt enable (WDIE)
+  sei();                                             // Turn interupts on
+  while (nrot > 0);
+}
+
+ISR(WDT_vect)
+{
+  nrot--;
+  seed = seed << 8;
+  seed = seed ^ TCNT1L;
+}
+
+void setup()
+{
+  unsigned long start_time;
+  unsigned long end_time;
+  unsigned long elapsed_time;
+
+  Serial.begin(9600);
+  start_time = micros();
+  CreateTrulyRandomSeed();
+  randomSeed(seed);
+  end_time = micros();
+  elapsed_time = end_time - start_time;
+  Serial.print("Completed seeding the PRNG in ");
+  Serial.print(elapsed_time);
+  Serial.println(" microseconds!");
+}
+
+void loop()
+{
+}
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