Re: Gecko drives and EMC

[Jon Elson <elson-at-pico-systems.com>]

Paul wrote:

>Hi Robin
>
>A 20KHz pulse rate equates to a PERIOD of 25uS (we need two interrupts for 
>each step). As an example, I have an 800MHz Duron running at 16uS, and an 
>Athlon 18000 down to ~8uS. I would have though a 1.2GHz box would be more 
>than capable of generating a 20KHz signal.
>There is one problem with running PERIOD at such small values - Interrupt 
>latency. Depending on the motherboard chipset and DMA activity, this *could* 
>be as high as 30uS. On a lightly loaded Athlon, I see around 10-14uS jitter 
>when running PERIOD under 10uS. Increasing this parameter to 20-30uS, and the 
>jitter dissappears.
>  
>
Maybe the microstepping drive compensates for the timing granularity at 
the maximum
rate, but it seems that the jump from 20 Khz down to the next slower 
speed would have to be
at least a jump to 13.333 KHz (3 ticks of a 25 uS clock = 75 uS).  You 
can try it with
software, and if it is not performing well enough, you can then throw 
some hardware
at the problem.

Jon