PFM to control spindle speed?

I've acquired a Denford Novamill which is a part complete 'convert to linuxCNC' project. It's come with a SpindleV3 PCB to convert a parallel port signal into the 0V to10V that the spindle speed controller expects. My problem is that the interface board expects PFM, zero to 2000 Hz pulses, but the StepConv wizard only offers PWM or PDM. Can I get LinuxCNC to produce PFM for spindle speed control?

Yes, you could use either a stepgen (in velocity mode) or the siggen component to generate the PFM

The Stepgen has the advantage that its frequency command scaling is adjustable
so the commanded RPM => frequency translation is done just by setting one parameter.

Great, how do I do this though?

Basically you edit your hal file to add the additional stepgen (set to velocity mode)
then set the scaling and width parameters for that stepgen and finally "net"
LinuxCNC spindle speed command pin to the spindle stepgens velocity command input
(and possibly net LinuxCNCs spindle on command to the stepgen enable pin)
 (man stepgen)

If you post your current hal/ini files, I can make some examples of the changes needed

That's brilliant, just the sort of guidance I need. I'll have a crack at it myself to start with.

It's taking me a while to get my head around the 969 pages of documentation, so I'd like to take you up on the offer of editing my hal/ini files (attached).

First step would be to add the new stepgen
To do that you would change

loadrt stepgen step_type=0,0,0

to

loadrt stepgen step_type=0,0,0,0 ctrl_type = p,p,p,v

(man stepgen)

This isn't going well. I put the following lines in the HAL:

loadrt stepgen step_type=0,0,0,0 ctrl_type = p,p,p,v
net spindle-cmd-rpm => stepgen.3.velocity-cmd
net spindle-on <= spindle.0.on => stepgen.3.enable
net spindle-pfm <= stepgen.3.step
setp stepgen.3.maxvel 5000.0
setp stepgen.3.position-scale 0.4
setp stepgen.3.steplen 230000
setp stepgen.3.stepspace 230000

LinuxCNC terminated immediately with errors below:
Invalid parameter 'ctrl_type'

Follow up edit, after staring at the code for ages I clock the extraeneous space characters either side of the =. I've left the post up for other newbies like me.

Sorry for the spaces in the example, the command line parser is quite picky...

I get that, if a space is a separator then it's a separator. As a veteran C/C++ coder I just don't 'see' spaces.