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jmelson wrote:
Just for the record, I'm using an Intel D425KT with a parallel port, which I think is still in production. Very nice board with low latency jitter values.

Btw, having jumped from the parallel port's software stepping to an FPGA hardware solution with closed pid loop, I'm sure I don't want to go back again. Closed loop is probably the top of the features that most people should value and use EMC for.
I also think (and this is probably an overstatement, but just to make my point here) that USB is a piece of crap for pretty much everything except keyboards and mice.
So, from my perspective, I'm pretty happy that EMC's developers make things this way and not Mach's way.

jmelson wrote:And over and over, 90% of use cases that uses open loop stepper motors does not need this round trip
because they are open loop. I have all time admitted that in these use cases where closed loop 50us loop
is required USB does not work. This is just limit that should be accepted when choosing technology.
In similar manner, it is not possible to get as much speed and force with steppers that you could get with servomotors.
Used technology should be selected use case basis and in most use cases steppers and USB are working choice.

Once again over and over, i have never even proposed removal any existing features from EMC, just
proposed one new, USB interface that can be used with steppers. I expect that 90% of emc users
uses it just as Mach, controlling open loop stepper controlled mill, plasma or lathe.
Why then have stepper interface at all if is just duplicating Mach ?

There is many other reasons to use EMC and not Mach. To me, EMC is GREAT software, i love it
and great thanks to developer. I am currently using it with open loop steppers with mill.
I chose EMC over Mach because I wanted Linux based FOSS software that i can manage and
tailor as i like.
I dot not say unobtainable, i just said that it becomes more and more difficult to obtain and
selection becomes smaller and smaller. Very difficult != unobtainable, Very difficult == very difficult to obtain

Kate

kostas wrote:
I succeeded to find VIA CPU based Travia C134, small compact box with parallel port. It just happened to have single core CPU without LAPIC and i needed to recompile kernel, rtai and emc from Live CD. I noticed that this was very common case because it was on FAQ but about no-one of basic users were able to do it.

What i have been looking, i estimate than more than 90% is running with steppers, so open loop. Closed loop is great thing in places where it is needed but when interface is open loop steppers, it is simply not needed. So, i value it as closed loop as a great feature that really gives more value in certain use cases but it just happens that my use case or use case of 90% of EMC users just does not need it. I still don't propose it's removal, it is important feature even it not needed in every use case.

I hope having some day BLDC servos replacing steppers. I would get more speed and torque. There is no technical reason why USB could not be used with BLDC when 50us servo PID loop is running on microcontroller, just similar way that it runs on brushed DC servo controller. Only difference is that pid loop runs with position mode, not speed mode, When input to controller is position command coming from 1ms loop, USB is enough fast .

Kate

kate wrote:FWIW I agree with this, and feel that EMC2 wouldn't necessarily lose anything by supporting (for example) SmoothStepper.
Someone has actually created a CNC machine using the Mesa 7i43 in USB mode, I am not sure how well it works in practice.
I am not sure that this is necessarily true, though.
The motion commands are sent to the hardware on the assumption that very nearly exactly 1ms later there will be another update. The acceleration and deceleration curves rely on this. I think that USB is allowed a worst-case latency of 4mS (but might be wrong). To an extent you can compensate with buffering the position commands, but I am not sure how you recover the buffer. I suppose running a few % fast might be allowable assuming that the long-latency packets are rare.
Sending the axis positions direct to a driver in HAL seems emminently doable, and is certainly no worse than using a step-dir servo drive. I don't think that sending the positions back to close the loop would work too well, as the data might get quite stale.

However, compared to using a realtime-friendly PCI card, using a USB-connnected uC seems like re-inventing the wheel, but giving it 4 corners in the process. (Note that the SmoothStepper is significantly more expensive than several of the PCI cards supported by EMC2)

andypugh wrote:
Do you also know, how does SmoothStepper's performance compare with other similar FPGA cards, Andy? Mesa's 7i43 for example.
I always wondered how does it perform using the USB interface under Windows.

kostas wrote:
No idea. As it is more expensive, doesn't work with EMC2 and runs on Windows (none of my machines ever have) it has never been of any interest.