OpenWrt
AvalonMiner 821: https://canaan.io/downloads/software/avalon821/openwrt/20181223/
AvalonMiner 841: https://canaan.io/downloads/software/avalon841/openwrt/20181223/
AvalonMiner 851: https://canaan.io/downloads/software/avalon851/openwrt/20181223/
MM
AvalonMiner 821: https://canaan.io/downloads/software/avalon821/mm/2018-12-22/
AvalonMiner 841: https://canaan.io/downloads/software/avalon841/mm/2018-12-22/
AvalonMiner 851: https://canaan.io/downloads/software/avalon851/mm/2018-12-22/
There are no published changelogs for all three OpenWrt firmware releases at the time of writing.
The changelogs for all three MM firmware releases read:
Version 8211812-d33ea90
* Support low power, modify volt adjusting method and certain ss params.
Version 8411812-d33ea90
* Support low power, modify volt adjusting method and certain ss params.
Version 8511812-e19ca70
* Support low power, modify volt adjusting method and certain ss params.
Interestingly, version 20181223 is treated as a new distinct branch in Canaan's GitHub repositories. Canaan calls it avalon8-lp here, here, and here.
Notable changes in version 20181223 include: