git submodule update issue

[tigertigerwang]

#git submodule update --init
fatal: remote error: upload-pack: not our ref f82b1f42224dd9cd8dabd037907c731f1b94a867
fatal: the remote end hung up unexpectedly
Fetched in submodule path 'libswiftnav', but it did not contain f82b1f42224dd9cd8dabd037907c731f1b94a867. Direct fetching of that commit failed.

[tigertigerwang]

piksi_firmware can not sync with libswiftnav, tried all branches, get same result.