Can now() roll over just like millis()?

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I'm using now() and millis() to trigger events after a certain time has passed.
I am aware, and it's also easily found on the web, that millis() rolls over after a certain time has passed and for code that has to run indefinitely you have to handle this.

However I am not aware of if now() can do the same at some point. I mean it does count the seconds from the 1.1.1970 so just regarding this fact, it should not roll over. However, just like millis() this has to be counted somewhere no? How does it work?

arduino-uno arduino-mega

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asked 3 hours ago

Streamline

134

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  What now() are you talking about? Could you give a reference?
  – Edgar Bonet
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @EdgarBonet probably arduino.cc/en/Reference/CurieTimeNow
  – Michel Keijzers
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  he asks about Epoch seconds in Arduino, as used by the TimeLib
  – Juraj
  2 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  It may be worth noting that you don't necessarily have to "handle" millis() rollover; you just have to prepare your comparison correctly, and there is no rollover problem, as long as you are trying to compare durations smaller than the maximum millis() value.
  – jose can u c
  2 hours ago
  

  
  
  
  

add a comment | 

up vote
1
down vote

favorite

I'm using now() and millis() to trigger events after a certain time has passed.
I am aware, and it's also easily found on the web, that millis() rolls over after a certain time has passed and for code that has to run indefinitely you have to handle this.

However I am not aware of if now() can do the same at some point. I mean it does count the seconds from the 1.1.1970 so just regarding this fact, it should not roll over. However, just like millis() this has to be counted somewhere no? How does it work?

arduino-uno arduino-mega

share|improve this question

asked 3 hours ago

Streamline

134

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  What now() are you talking about? Could you give a reference?
  – Edgar Bonet
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @EdgarBonet probably arduino.cc/en/Reference/CurieTimeNow
  – Michel Keijzers
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  he asks about Epoch seconds in Arduino, as used by the TimeLib
  – Juraj
  2 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  It may be worth noting that you don't necessarily have to "handle" millis() rollover; you just have to prepare your comparison correctly, and there is no rollover problem, as long as you are trying to compare durations smaller than the maximum millis() value.
  – jose can u c
  2 hours ago
  

  
  
  
  

add a comment | 

up vote
1
down vote

favorite

up vote
1
down vote

favorite

I'm using now() and millis() to trigger events after a certain time has passed.
I am aware, and it's also easily found on the web, that millis() rolls over after a certain time has passed and for code that has to run indefinitely you have to handle this.

However I am not aware of if now() can do the same at some point. I mean it does count the seconds from the 1.1.1970 so just regarding this fact, it should not roll over. However, just like millis() this has to be counted somewhere no? How does it work?

arduino-uno arduino-mega

share|improve this question

asked 3 hours ago

Streamline

134

I'm using now() and millis() to trigger events after a certain time has passed.
I am aware, and it's also easily found on the web, that millis() rolls over after a certain time has passed and for code that has to run indefinitely you have to handle this.

However I am not aware of if now() can do the same at some point. I mean it does count the seconds from the 1.1.1970 so just regarding this fact, it should not roll over. However, just like millis() this has to be counted somewhere no? How does it work?

arduino-uno arduino-mega

arduino-uno arduino-mega

share|improve this question

asked 3 hours ago

Streamline

134

share|improve this question

asked 3 hours ago

Streamline

134

share|improve this question

share|improve this question

asked 3 hours ago

Streamline

134

asked 3 hours ago

Streamline

134

asked 3 hours ago

Streamline

134

134

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  What now() are you talking about? Could you give a reference?
  – Edgar Bonet
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @EdgarBonet probably arduino.cc/en/Reference/CurieTimeNow
  – Michel Keijzers
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  he asks about Epoch seconds in Arduino, as used by the TimeLib
  – Juraj
  2 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  It may be worth noting that you don't necessarily have to "handle" millis() rollover; you just have to prepare your comparison correctly, and there is no rollover problem, as long as you are trying to compare durations smaller than the maximum millis() value.
  – jose can u c
  2 hours ago
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  What now() are you talking about? Could you give a reference?
  – Edgar Bonet
  3 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  @EdgarBonet probably arduino.cc/en/Reference/CurieTimeNow
  – Michel Keijzers
  2 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  he asks about Epoch seconds in Arduino, as used by the TimeLib
  – Juraj
  2 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  It may be worth noting that you don't necessarily have to "handle" millis() rollover; you just have to prepare your comparison correctly, and there is no rollover problem, as long as you are trying to compare durations smaller than the maximum millis() value.
  – jose can u c
  2 hours ago
  

  
  
  
  

2

2

What now() are you talking about? Could you give a reference?
– Edgar Bonet
3 hours ago

What now() are you talking about? Could you give a reference?
– Edgar Bonet
3 hours ago

@EdgarBonet probably arduino.cc/en/Reference/CurieTimeNow
– Michel Keijzers
2 hours ago

@EdgarBonet probably arduino.cc/en/Reference/CurieTimeNow
– Michel Keijzers
2 hours ago

he asks about Epoch seconds in Arduino, as used by the TimeLib
– Juraj
2 hours ago

he asks about Epoch seconds in Arduino, as used by the TimeLib
– Juraj
2 hours ago

It may be worth noting that you don't necessarily have to "handle" millis() rollover; you just have to prepare your comparison correctly, and there is no rollover problem, as long as you are trying to compare durations smaller than the maximum millis() value.
– jose can u c
2 hours ago

It may be worth noting that you don't necessarily have to "handle" millis() rollover; you just have to prepare your comparison correctly, and there is no rollover problem, as long as you are trying to compare durations smaller than the maximum millis() value.
– jose can u c
2 hours ago

add a comment | 

2 Answers
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up vote
2
down vote

If now() is from the TimeLib.h library, then this definition:

typedef unsigned long time_t;

indicates time_t is 32-bit unsigned value. Since it represents seconds since 1970-Jan-01 00:00:00, it will experience a rollover when representing dates past approximately 2106 (1970-Jan-01 + 2^32 seconds). Being unsigned, it also cannot represent dates earlier than 1970-Jan-01.

This is slightly different than the 2038 Rollover Problem, which occurs when a system defines a time_t as a signed 32-bit integer, and thus experiences this rollover earlier, in year 2038.

All of this depends on how/where the type time_t is defined for your CPU architecture, and this answer assumes an 8-bit AVR like Arduino Uno. If you use a different architecture, for which TimeLib.h has a different type definition, read the source code to find out exactly what you're dealing with.

share|improve this answer

edited 2 hours ago

answered 2 hours ago

jose can u c

5,1372624

• 
  
  
  

  
  

  
  
  
  
  
  

  
  sorry, long is 32 bits on 32 bits system too
  – Juraj
  4 mins ago
  
  

  
  
  
  

add a comment | 

up vote
2
down vote

now() is a function that is specific to Intel Curie based boards.

It returns an unsigned long (which on a 32-bit system is the same as an unsigned int) and so can provide the number of seconds since 1/1/1970 up until the year 2106, at which point it will roll over.

If you plan on having your system run continuously for more than the next 88 years you will have to deal with that rollover correctly, including:

• Using subtraction to "wrap around" your calculations


• Not trying to calculate any periods longer than 136 years

share|improve this answer

answered 2 hours ago

Majenko♦

63k42873

add a comment | 

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

up vote
2
down vote

If now() is from the TimeLib.h library, then this definition:

typedef unsigned long time_t;

indicates time_t is 32-bit unsigned value. Since it represents seconds since 1970-Jan-01 00:00:00, it will experience a rollover when representing dates past approximately 2106 (1970-Jan-01 + 2^32 seconds). Being unsigned, it also cannot represent dates earlier than 1970-Jan-01.

This is slightly different than the 2038 Rollover Problem, which occurs when a system defines a time_t as a signed 32-bit integer, and thus experiences this rollover earlier, in year 2038.

All of this depends on how/where the type time_t is defined for your CPU architecture, and this answer assumes an 8-bit AVR like Arduino Uno. If you use a different architecture, for which TimeLib.h has a different type definition, read the source code to find out exactly what you're dealing with.

share|improve this answer

edited 2 hours ago

answered 2 hours ago

jose can u c

5,1372624

• 
  
  
  

  
  

  
  
  
  
  
  

  
  sorry, long is 32 bits on 32 bits system too
  – Juraj
  4 mins ago
  
  

  
  
  
  

add a comment | 

up vote
2
down vote

If now() is from the TimeLib.h library, then this definition:

typedef unsigned long time_t;

indicates time_t is 32-bit unsigned value. Since it represents seconds since 1970-Jan-01 00:00:00, it will experience a rollover when representing dates past approximately 2106 (1970-Jan-01 + 2^32 seconds). Being unsigned, it also cannot represent dates earlier than 1970-Jan-01.

This is slightly different than the 2038 Rollover Problem, which occurs when a system defines a time_t as a signed 32-bit integer, and thus experiences this rollover earlier, in year 2038.

All of this depends on how/where the type time_t is defined for your CPU architecture, and this answer assumes an 8-bit AVR like Arduino Uno. If you use a different architecture, for which TimeLib.h has a different type definition, read the source code to find out exactly what you're dealing with.

share|improve this answer

edited 2 hours ago

answered 2 hours ago

jose can u c

5,1372624

• 
  
  
  

  
  

  
  
  
  
  
  

  
  sorry, long is 32 bits on 32 bits system too
  – Juraj
  4 mins ago
  
  

  
  
  
  

add a comment | 

up vote
2
down vote

up vote
2
down vote

If now() is from the TimeLib.h library, then this definition:

typedef unsigned long time_t;

indicates time_t is 32-bit unsigned value. Since it represents seconds since 1970-Jan-01 00:00:00, it will experience a rollover when representing dates past approximately 2106 (1970-Jan-01 + 2^32 seconds). Being unsigned, it also cannot represent dates earlier than 1970-Jan-01.

This is slightly different than the 2038 Rollover Problem, which occurs when a system defines a time_t as a signed 32-bit integer, and thus experiences this rollover earlier, in year 2038.

All of this depends on how/where the type time_t is defined for your CPU architecture, and this answer assumes an 8-bit AVR like Arduino Uno. If you use a different architecture, for which TimeLib.h has a different type definition, read the source code to find out exactly what you're dealing with.

share|improve this answer

edited 2 hours ago

answered 2 hours ago

jose can u c

5,1372624

If now() is from the TimeLib.h library, then this definition:

typedef unsigned long time_t;

indicates time_t is 32-bit unsigned value. Since it represents seconds since 1970-Jan-01 00:00:00, it will experience a rollover when representing dates past approximately 2106 (1970-Jan-01 + 2^32 seconds). Being unsigned, it also cannot represent dates earlier than 1970-Jan-01.

This is slightly different than the 2038 Rollover Problem, which occurs when a system defines a time_t as a signed 32-bit integer, and thus experiences this rollover earlier, in year 2038.

All of this depends on how/where the type time_t is defined for your CPU architecture, and this answer assumes an 8-bit AVR like Arduino Uno. If you use a different architecture, for which TimeLib.h has a different type definition, read the source code to find out exactly what you're dealing with.

share|improve this answer

edited 2 hours ago

answered 2 hours ago

jose can u c

5,1372624

share|improve this answer

share|improve this answer

edited 2 hours ago

edited 2 hours ago

edited 2 hours ago

answered 2 hours ago

jose can u c

5,1372624

answered 2 hours ago

jose can u c

5,1372624

answered 2 hours ago

jose can u c

5,1372624

5,1372624

• 
  
  
  

  
  

  
  
  
  
  
  

  
  sorry, long is 32 bits on 32 bits system too
  – Juraj
  4 mins ago
  
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  sorry, long is 32 bits on 32 bits system too
  – Juraj
  4 mins ago
  
  

  
  
  
  

sorry, long is 32 bits on 32 bits system too
– Juraj
4 mins ago

sorry, long is 32 bits on 32 bits system too
– Juraj
4 mins ago

add a comment | 

up vote
2
down vote

now() is a function that is specific to Intel Curie based boards.

It returns an unsigned long (which on a 32-bit system is the same as an unsigned int) and so can provide the number of seconds since 1/1/1970 up until the year 2106, at which point it will roll over.

If you plan on having your system run continuously for more than the next 88 years you will have to deal with that rollover correctly, including:

• Using subtraction to "wrap around" your calculations


• Not trying to calculate any periods longer than 136 years

share|improve this answer

answered 2 hours ago

Majenko♦

63k42873

add a comment | 

up vote
2
down vote

now() is a function that is specific to Intel Curie based boards.

It returns an unsigned long (which on a 32-bit system is the same as an unsigned int) and so can provide the number of seconds since 1/1/1970 up until the year 2106, at which point it will roll over.

If you plan on having your system run continuously for more than the next 88 years you will have to deal with that rollover correctly, including:

• Using subtraction to "wrap around" your calculations


• Not trying to calculate any periods longer than 136 years

share|improve this answer

answered 2 hours ago

Majenko♦

63k42873

add a comment | 

up vote
2
down vote

up vote
2
down vote

now() is a function that is specific to Intel Curie based boards.

It returns an unsigned long (which on a 32-bit system is the same as an unsigned int) and so can provide the number of seconds since 1/1/1970 up until the year 2106, at which point it will roll over.

If you plan on having your system run continuously for more than the next 88 years you will have to deal with that rollover correctly, including:

• Using subtraction to "wrap around" your calculations


• Not trying to calculate any periods longer than 136 years

share|improve this answer

answered 2 hours ago

Majenko♦

63k42873

now() is a function that is specific to Intel Curie based boards.

It returns an unsigned long (which on a 32-bit system is the same as an unsigned int) and so can provide the number of seconds since 1/1/1970 up until the year 2106, at which point it will roll over.

If you plan on having your system run continuously for more than the next 88 years you will have to deal with that rollover correctly, including:

• Using subtraction to "wrap around" your calculations


• Not trying to calculate any periods longer than 136 years

share|improve this answer

answered 2 hours ago

Majenko♦

63k42873

share|improve this answer

share|improve this answer

answered 2 hours ago

Majenko♦

63k42873

answered 2 hours ago

Majenko♦

63k42873

answered 2 hours ago

Majenko♦

63k42873

63k42873

add a comment | 

add a comment | 

 

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