Handling time in embedded systems is not only about keeping accurate time, but also about storing, transmitting and processing it efficiently. One of the most widely used representations is Unix time, also known as epoch time.
This article explains Unix time, common time formats and how they are used in embedded systems.
What Is Unix Time?
Unix time is a simple way to represent time as a single number.
- Counts seconds since January 1, 1970 (UTC)
- Also called "epoch time"
- Does not include time zones or DST
This makes it easy to store and compare time values.
Why Unix Time Is Useful
- Compact representation (single integer)
- Easy arithmetic (add/subtract seconds)
- Platform-independent
It is widely used in IoT devices, servers and embedded systems.
Example
Unix timestamp:
- 0 → Jan 1, 1970 00:00:00 UTC
- 1700000000 → Approx. Nov 2023
The exact date can be calculated in software.
32-bit vs 64-bit Time
32-bit Systems
- Maximum value: 2,147,483,647
- Overflow in 2038 (Year 2038 problem)
64-bit Systems
- Practically unlimited range
- No overflow concerns
Modern systems increasingly use 64-bit timestamps.
Human-Readable Time Formats
ISO 8601
- Format: YYYY-MM-DD HH:MM:SS
- Example: 2026-04-27 14:30:00
Custom Formats
- HH:MM:SS
- MM/DD/YYYY
These formats are used for display, not internal processing.
Conversion Between Formats
Embedded systems often need to convert between Unix time and human-readable formats.
- Unix → date/time (for display)
- Date/time → Unix (for storage)
This requires calendar calculations, including leap years.
Time Storage in RTCs
RTC chips such as DS1307 and DS3231 do not use Unix time internally.
- Store time in BCD format
- Separate registers for seconds, minutes, hours, etc.
Conversion to Unix time is done in software.
Handling Time Zones
Unix time is always in UTC.
- No built-in time zone information
- Conversion required for local time
This is why UTC should be used internally.
Common Use Cases
Data Logging
- Store timestamps efficiently
- Easy to sort and compare
Communication
- Standard format across systems
- Used in APIs and protocols
Scheduling
- Simple time comparisons
- Trigger events at specific times
Precision Considerations
- Standard Unix time: seconds resolution
- Extended formats: milliseconds or microseconds
Higher precision may be required for advanced applications.
Common Mistakes
- Using local time instead of UTC
- Ignoring 2038 problem on 32-bit systems
- Incorrect conversion between formats
Best Practices
- Use Unix time internally
- Convert to human-readable format only when needed
- Use 64-bit timestamps for future-proof design
Example Workflow
- Read time from RTC or NTP
- Convert to Unix timestamp
- Store or process time
- Convert back to readable format for display
Conclusion
Unix time provides a simple and powerful way to handle time in embedded systems. It simplifies storage, comparison and communication while avoiding many of the complexities of human-readable formats.
By using Unix time internally and converting to readable formats only when necessary, you can build robust and scalable time-based applications.