Why only first half of register bank is accessible in VFP's S0-31 register bank?


I am working on an ALU Supervisor with armv7-M.

Everything in documentation seem to say if cp10 and cp11 are activated, s0-s31 are accessible. Everything works fine with s0-s15

Though when trying to perform simple operation like

vmov.f32 s16,s15

Register s16 stay at 0.0

I can modify the value via WinIdea but it seem the whole s16-s31 bank is reset to zero when I try to access it again.

Is there something so configure before accessing these registers ?