Web lists-archives.com

Re: SSD's and many edits of a single file


On Thursday, April 12, 2018 08:43:50 AM Gene Heskett wrote:
> On Thursday 12 April 2018 07:44:39 rhkramer@xxxxxxxxx wrote:
> > On 2nd reading, I think the answer is yes, i.e., if I have a midi
> > program making use of the / a real time kernel, it will have total
> > control of the machine and other programs will have the "leftovers"?
> Yes. Particularly noticeable if running the steppers by software step
> generation. There, one must run a "base thread", limited to integer only
> math, in a 20 to 30 nanosecond loop. Because the loop is so slow, this
> function is often off-loaded to an fpga smart card that is programmed at
> a 1 to 10 kilohertz rate with most using the default 1 kilohertz.  This
> can quadruple the speeds, from 2 effects. Because the motors see a much
> steadier heartbeat, they can often be moved much faster without
> stalling, and 2, this hardware can often generate the step signals 10x
> faster.
> OTOH, doing that also frees up the parent cpu, allowing it to do much
> more without affecting the main process.
> We can also setup slower "threads" for stuff that are the result of human
> activity for instance. Humans are rather glacial movers.
> For less critical duties this works well, and in the case of running
> bigger machinery with something as puny-powered as an r-pi-3b, I have
> much of the not so time critical stuff running in a 200 hz thread, so
> that nearly half of the hal file only gets processed when the higher
> priority, faster loop is done. This includes the hand driven encoder
> dials that allow me to run the lathe by hand. Even at 200 hz I can still
> drive it at anything from the maximum speed of nearly 90 inches a
> minute, down to as small as .0001" per click of the dial. Thats a larger
> movement than the software itself can do since if I tell it to move 12"
> along the bed, while moving the cross-feed 3 thousandths of an inch, it
> will do what is effectively a dead straight line from that start to that
> finish. Errors in that motion are generally the coil current mappings of
> the stepper driver as it divides a full step, 1/200th of a turn, by 8 or
> 16 in order to get that smoother motion. Loading of course inserts an
> offset, but is under a .9 degree of the motor shaft rotation as long as
> the load doesn't cause a step slip. That much may break the micron
> claim, but not by enough to ruin the part.
> Lots of other stuff that would be TL;DR for most here.