How to Embed Software Version, Build Date, and Time into Flash with Keil MDK

In many embedded projects, adding version information to the firmware is essential for tracking releases and debugging. This article shares a common technique for writing software version, compile date, and compile time into a specific Flash region using the Keil MDK environment.

Implementation Method

The approach stores strings at fixed Flash addresses by leveraging the GCC-style __attribute__((at(address))) syntax. Example code:

#define VERINFO_ADDR_BASE   (0x0800FF00) // Flash storage base address

const char Software_Ver[] __attribute__((at(VERINFO_ADDR_BASE + 0x00))) = "Software: 1.0.0";
const char Compiler_Date[] __attribute__((at(VERINFO_ADDR_BASE + 0x40))) = "Date: "__DATE__;
const char Compiler_Time[] __attribute__((at(VERINFO_ADDR_BASE + 0x60))) = "Time: "__TIME__;

This code places three null‑terminated strings at the defined addresses, allowing the firmware to read version information at runtime.

Understanding __attribute__

The __attribute__ keyword lets you assign special properties to functions, variables, or types. The general form is __attribute__((attribute-list)). For placing data in Flash, the at(address) attribute is used.

Standard C Predefined Macros

Two useful predefined macros are demonstrated: __DATE__ – compilation date string (e.g., "Apr 13 2021"). __TIME__ – compilation time string (e.g., "20:00:00").

Other macros such as __FILE__, __LINE__, and __STDC__ are mentioned for reference.

Ensuring Correct Build Information

Keil MDK may not rebuild source files automatically, so the "Always Build" option must be enabled to guarantee that the version, date, and time strings are updated on each compilation.

Reducing Firmware Size

Generated HEX files pad unused Flash with 0x00, inflating size. Two strategies are suggested:

Place the version info at an appropriate Flash address to avoid excessive offset padding.

Adjust the ROM size setting in the project options to eliminate unnecessary padding.

Both methods can shrink the final binary, but they carry risk if the code size grows beyond the allocated region, so careful Flash layout planning is advised.

Key Takeaways

Use __attribute__((at(address))) to embed constant strings in Flash.

Leverage __DATE__ and __TIME__ for automatic build timestamps.

Enable "Always Build" in Keil MDK to keep version data current.

Optimize Flash placement and ROM size to keep firmware binaries compact.