Can negative values be mapped to pwmgen? For Bridgeport TC22/DX32 conversion

I'm considering doing a LinuxCNC conversion on my Bridgeport TorqueCut 22. This machine has a somewhat unique motor drive configuration where they have digital DC servo amps which are essentially just H bridges and a small CPLD. Each axis receives a 25kHz PWM signal for control 0-100% duty cycle where 50% duty is zero current. Over 50% duty is positive current, <50% duty is negative. The CPLD maps the PWM directly into a 25khz drive waveform for the boards Hbridge. There is one of these cards per axis. If I did a conversion it would be elegant to just reuse these drivers. They work fine and are well matched to the machine's motors. Would pwmgen support this type of mapping? 

I apologize if this has been asked before at some point. I searched around and didn't find another similar thread. There are a few of these machines out there that have been converted but I believe in all cases so far new analog servo amps were used, or in one case the machine was converted to all AC servo's/controllers (obviously the COOLEST approach but also the highest budget/effort).

Thank you!


James
 

Depends on the PWM generator

The Mesa hm2 driver can do this ("offset" mode)
but even if this is not supported directly, it
can be done in hal using the offset component

Makes sense. The pwmgen will just do as the hal asks it. I'll fool around with this and see if I can get it to work. Thank you!

Does it need single phase or three phase PWM? (The Mesa firmware can do both)