Inactive tool spindle speed update only works once

[svp_vub]

Updating the speed of a spindle that is not the currently active tool seems to work only once.

T0
M3 P1 S200 ; works
M3 P1 S500 ; does not work

If we set the active tool with T1 it works.

When we try to change it through M4 it works but again only once:

T0
M3 P1 S200 ; works
M4 P1 S500 ; works
M4 P1 S1000 ; does not work
M3 P1 S1000 ; works

Is this the expected behavior, and if so what is the reason?

We checked the code and it seems to come from these lines:
https://github.com/Duet3D/RepRapFirmware/blob/1194bf3d4867a844fe442cfc7d1500d933521467/src/GCodes/GCodes2.cpp#L583-L586
And especially this one where the rpm is updated if there is a state change
https://github.com/Duet3D/RepRapFirmware/blob/1194bf3d4867a844fe442cfc7d1500d933521467/src/Tools/Spindle.cpp#L134-L141

[T3P3Tony]

@svp_vub which version of RRF are you running? I cant see this is expected behaviour.

[dc42]

@svp_vub I confirm this is a bug. We will fix it in 3.5beta3 and probably also in 3.4.6.

[svp_vub]

@dc42 ok thanks a lot! Out of curiosity, do you already know what will become the expected behavior? Will we be able to update the spindle speed if it is not the currently active tool?

[dc42]

@svp_vub yes you will.