hw stepper card, linuxcnc, top view?!

perfect!!! thanks a bunch ...

one more question if you don't mind

I just opened this box I dedicated for that work and I see I have both free pci-e and pci slots .. the 20e difference between pcie and pci version makes no difference to me so moneywize it's irrelevant .. but any difference between 6i25 and 5i25 except for interface towards computer (pci vs pci-e)? any latency difference between pci and pci-e with linuxcnc?

arhi wrote: if someone can point me to a top level explanation how these hw steppers work

They work rather a lot like how the software stepper works.
The software stepper has a function "update-freq" which runs in the servo thread at (typically) 1kHz. Then there is a "make-pulses" function that runs in the base-thread which does almost no calculations, it just makes pulses at the frequency commanded by "update-freq"

The "update-freq" function looks at the current motor position (total step count, rather than any real feedback) and calculates how many steps are needed to get to the commanded position by the end of the next servo period.

The Mesa cards work in almost exactly the same way. The Hostmot2 driver receives position commands from LinuxCNC every servo-cycle, then this is converted into a step frequency by the hostmot2 stepper driver code running on the PC
The required step rate is passed to a register on the FPGA using whatever interface and low-level driver is in use.
Then the FPGA code makes steps at the desired rate.

arhi wrote: any latency difference between pci and pci-e with linuxcnc?

None that matters in the context of overall system latency.

perfect, many thanks for confirming ... so I can have 1 THz stepping if I want (can execute on the hw step generator) and I communicate to step generator ever "servo period".. great .. so in theory I can use usb/ethernet/uart.. too to make the hw stepper as long as I can achieve the "data exchange" every "servo period"... nice thanks!! off to read some source

arhi wrote: perfect, many thanks for confirming ... so I can have 1 THz stepping if I want (can execute on the hw step generator) and I communicate to step generator ever "servo period"

In principle, yes. However it probably doesn't make sense to have more than a few orders of magnitude difference between step rate and update rate.

(Also, you will probably find it hard to make and program your own FPGA more cost-effectively than just buying a Mesa card, the cheapest one is $59 and the price drops quickly with volume.)

andypugh wrote: In principle, yes. However it probably doesn't make sense to have more than a few orders of magnitude difference between step rate and update rate.

of course, yes .. just testing the logic nothing else ..

andypugh wrote: (Also, you will probably find it hard to make and program your own FPGA more cost-effectively than just buying a Mesa card, the cheapest one is $59 and the price drops quickly with volume.)

I don't have a problem to program fpga I just have problem I don't have time to spend with my kid let alone invent hot water so of course I'm getting a ready/tested product ... I'm more interested in this as an idea then as something I'd implement ... attm my puny machine runs more then ok from a parallel port ... I'll get mesa card just for future updates ... the 2 daughters with a pci-e card solves kinda all my current and future neads + I was looking at these mesa links you gave me, I could use these cards for some other stuff ... but that's another story .. Thanks!