emCompress

SEGGER emCompress is a family of data compression libraries optimised for embedded systems where ROM and RAM are limited but data reduction is essential, firmware update images, logged sensor data, web assets served from flash, and configuration files stored on-chip. Rather than offering a single algorithm, emCompress provides multiple editions, each targeting a different trade-off between compression ratio, decompression speed, and memory footprint. All editions are written in well-commented ANSI C, independent of compiler and target, and delivered as source code with royalty-free licensing.

Editions and Algorithms

emCompress-Pro and emCompress-ToGo both support on-the-fly streaming, receiving a data stream and decompressing it as bytes arrive, which is critical for firmware update scenarios where the full compressed image cannot be buffered in RAM. emCompress-Embed provides a wider selection of classic algorithms for projects that need to match a specific format or optimise for decode speed.

Use Cases

Watch the SEGGER emCompress introduction

emCompress is widely used for reducing the size of firmware update packages (paired with emLoad or emSecure for secure delivery), compressing logged data on storage-limited devices, and shrinking web assets served by emWeb. Because there are no open-source or attribution requirements, emCompress can ship in commercial products without licence disclosure concerns. The modular architecture means only the selected algorithm is linked into the final binary, keeping code size to a minimum.

Choosing an Edition

• emCompress-Pro: pick this when the highest compression ratio and full compress-plus-decompress streaming matter more than decoder footprint, such as bidirectional data links or two-way firmware exchange
• emCompress-ToGo: pick this when the decompressor must be as small as possible, for example a bootloader that only ever decompresses, never compresses, an incoming firmware image
• emCompress-Embed: pick this when a project needs to match an existing external file format (DEFLATE for ZIP compatibility, LZW, or RLE) rather than choosing SEGGER’s own algorithm
• emCompress-LZMA: pick this for the largest single-shot payloads, such as full firmware images, where LZMA’s ratio advantage outweighs its lower throughput

SEGGER Ecosystem Integration

emCompress is designed to slot into an existing SEGGER-based update pipeline rather than operate in isolation. A typical firmware delivery flow compresses the image with emCompress-LZMA or emCompress-Pro, signs it with emSecure, transports it over emNet or emUSB, and decompresses and applies it with emLoad or emBoot-Secure on the target. Because every stage in that pipeline is licensed royalty-free with a one-time payment, adding compression does not introduce a new per-unit cost on top of the update mechanism already in use.