It looks like rsta2/uspi rewrote their history or force-pushed something they shouldn't at some point and now the pigfx submodule is broken. Repo currently submodules fbergama/pigfx@afcfc39
which in turn submodules rsta2/uspi@7344968 even though that commit no longer exists.

error: no such remote ref 6620411c61332b468939baa2ecca61496b0b99f8
Fetched in submodule path 'uspi', but it did not contain 6620411c61332b468939baa2ecca61496b0b99f8. Direct fetching of that commit failed.

Issue was reported upstream in fbergama/pigfx#1 and submodule was updated and merged into master at fbergama/pigfx@ca52ea1.

Only just bought my RC2014 and still finishing the soldering and getting to grips with the code, so I don't know what else in this repo could be impacted by updating from upstream. There have only been 3 commits since the version currently referenced, but I don't know what they might break. One of them is the fix referenced above, another is fixing an escape key bugfix, but the earliest one is updating uspi to a newer version.

If someone with more Z80 experience and a working toolchain please look at this and update the submodule to either master or fbergama/pigfx/issue_1_fix?