Re: [CAD_CAM_EDM_DRO] Windows timing subroutines, how do they work?

Hi Alan,

The Mach2/3 driver is not a normal windows task. It installs itself as
an interrupt handler for the timer then reprograms the interrupt
controller to make the timer the highest priority. The task scheduler is
also interrupt driven but as it is now at a lower priority the Mach2
driver will be serviced before the task scheduler. The driver is then
fed from the main Mach2 application which runs as a normal high priority
Windows task. The application communicates with the driver through a
circular buffer. Each entry in the buffer is the equivalent to one cycle
of EMC's servo loop. EMC works out the velocities in real time every x
milliseconds while Mach2 calculates them in advance. The buffer is
continually filled from Mach2 and emptied by the driver. There are a few
weaknesses in this arrangement:

DMA or any hardware that disables the CPU will of course interrupt the
pulses. This is the case with any software based pulser including EMC.
Some applications and services such as qttask reprogram the timer and/or
interrupt controller causing the driver to run slow or end up running at
a lower priority.
If the system is heavily loaded and Mach2 does not keep the circular
buffer full the pulses will abruptly halt until Mach2 catches up then
they will abruptly start up again. Using a bigger circular buffer helps
but slows down jogging/pause response. This is why response can become
very choppy for slow CPUs. It doesn't help that the driver is taking up
a fair percentage of CPU time.

Les


KM6VV wrote:

>Hi Les,
>
>Interrupt priority? That's it? But isn't it more like the highest TASK
>priority? the pulse stream could still be delayed or altered if another task
>was still "taking it's good sweat time", and not relinquishing control. Do you
>have more detail?
>
>Alan KM6VV
>
>
>