vendor._altera: implement lib.io buffer primitives.

[wanda-phi]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.47%. Comparing base (6857daf) to head (4e2a653).
Report is 5 commits behind head on main.

❗ Current head 4e2a653 differs from pull request most recent head fed22cf. Consider uploading reports for the commit fed22cf to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1284      +/-   ##
==========================================
- Coverage   90.56%   90.47%   -0.09%     
==========================================
  Files          44       44              
  Lines       10638    10644       +6     
  Branches     2595     2307     -288     
==========================================
- Hits         9634     9630       -4     
- Misses        818      823       +5     
- Partials      186      191       +5     

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[tpwrules]

Switched my design to this branch and it works well with Quartus 20.1.1.720. It only uses basic I/O though, not even bidirectional.

[whitequark]

LGTM. This is still not perfect but the Altera users will simply have to share our suffering.