What to do to get latency figures down?

[CaptainVee]

The pc I use has high latency figures, over 50,000 and I'd like to get them down. It is a 733 Mhz P4 with 256 mb ram.

All the info I can find says stuff like "The video card can often be the cause of High..." Now I have tried an old one I had but that did not change anything.

Do you have any recommendations of things that I can simply try out to try and reduce the figures?

[wendtmk]

You might try some of the suggestions located in the wiki:

http://wiki.linuxcnc.org/cgi-bin/emc...roubleShooting

Mark

[Reax]

ADD LOTS MORE RAM

[jmelson]

Originally Posted by Reax ADD LOTS MORE RAM

Actually, this is the least likely thing to fix it. All RT tasks are locked in memory, as well as the
RT scheduler. So, if memory is short, either a task will not load at all, or it will run fine while the
rest of the system (Linux) croaks. The cause of poor latency results is usually a board that has a section of the driver using BIOS ROM code on the board, a board that is doing a lot of DMA I/O between it and memory, or SMI interrupts. Some of the latest motherboards have laptop-like features where the CPU is interrupted to control fan speed, check the battery which it doesn't even have, and all sorts of other stuff that would have been better handled in other ways. There are ways to turn off these functions on some motherboards.

I have been using Dell Optiplex machines for some time with good results on EMC2. Some of the older ones have on-board video that shares system memory, and you need to disable that and plug in a PCI video board. The Optiplex is their commercial grade system, not the home grade stuff.
I usually see latency that reaches about 11 us (11000 the way the EMC2 test displays it) under the worst-case testing.

I have also pretty much given up using anything with less than a 1 GHz CPU. Especially for use with software step pulse generation (no hardware pulse generator) you really need more than 733 MHz.

Jon

[samco]

depending on the chipset.. It may be an smi issue. http://wiki.linuxcnc.org/cgi-bin/emc...ixingSMIIssues

(also - don't plug any usb memory sticks in also - some older motherboards have latency issues when they are plugged in and out)

sam