#6 [Schematics] S901: No 1v8 decoupling

speaks for itself.

Although the abscence of vddio power supply decoupling is in the datasheet I'm not really sure we should follow this in this particular case. Especially given power supply being noisy on previous prototypes, it was noisy because of poor design, you know.

When power noise hits the IC there is a nonlinear reaction happening where noise might even increase itself via loop or imprint on the other signals. It is really better not to give power noise any easy entrance into IC even when it seems low-current and fluffy.