Interfacing to smart driver modules, where do I start?

I'm a newbie on LinuxCNC but I'm looking to control a three axis CNC mill that includes smart stepper drives. The interface to the stepper drives is through serial commands that allow you to control speed and position. I'm an experienced C/C++ coder, so I'm comfortable with low level interfacing, but I don't know what I need to do. Where do I start?

What type of interface do the step motor drives have?

ASCII commands,VE????? sets speed, FP???? sets position, stuff like that. The interfaces are Ethernet and RS485, so reasonably quick.

Sounds like fun...

Ideally you would want to remain in the realtime layer. I think that this might be easiest using a Mesa FPGA card with UART firmware.
Here is a simple Mesa UART driver written in the LinuxCNC comp preprocessing language. github.com/LinuxCNC/linuxcnc/blob/master...ivers/mesa_uart.comp

It _might_ be possible to send serial data out of the PC serial port, do you know if that is possible with simple inb() and outb() commands?
linuxcnc.org/docs/2.7/html/man/man3/rtapi_inb.3rtapi.html

With either approach you would create HAL input pins for your driver component that would be linked to the joint.N.motor-pos-cmd HAL pins from the motion controller.

Thanks for that, I don't understand it all but it does look really useful (and interesting). I'm sure I'll have some supplemental questions.