PFM to control spindle speed?

BTW you can use halcmd to try things out:

~/linuxcnc-dev/scripts$ halcmd -kf
halcmd: loadrt stepgen step_type=0,0,0,0 ctrl_type=p,p,p,v
halcmd: show pin stepgen
Component Pins:
Owner Type Dir Value Name
57 s32 OUT 0 stepgen.0.counts
57 bit OUT FALSE stepgen.0.dir

SNIP

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I've been using halcmd some, mostly to show pins. Looks to me like the spindle man page is way out of date compared with what 'show pin spindle.0.' reports.