ESP32 Compression

Progress

zlib

• Compressed a txt file (see demo.txt) to .gz archive with a C/R (compression ratio) of ~2.25
• Inflated the .gz archive back to the original file on ESP32
• Compressed a .bin file (e.g Core Dump generated from ESP32 on panic) to .gz archive with a C/R of 5.00
• .gz archive can be extracted on a host machine (Linux, Windows)
• With a memory usage of 27K at peak, zlib gave a C/R of 2.38 for demo.txt
• Config for above results -> window_bits: 12 | mem_level: 3 (See zlib Manual - Advanced Functions)
• WIP: Binary files compression (e.g. OTA images, Core Dump images)

brotli

• Compressed a txt file (see demo.txt) to .br file with a C/R of ~2.17
• Decompressed the .br file on ESP32
• Pros: Fast Compression and decompression (about 8x faster than zlib)
• Cons: High binary size (about 600K of flash is used for brotli)
• Cons: High memory usage for compression and decompression (about 50-60K at peak!)
• Tried compressing the file in chunks (rather than all at once as given in example), but C/R fell with no significant decrease in memory usage

Miscellaneous

• Compiled miniz but could not get it working; always seem to run out of RAM
• WIP: Find more compression libraries with embedded systems support
• Note: Flash memory has limited read/write cycles. Thus, file systems with wear-levelling should be used.