HP DC7600 - Latency not as reported in the wiki

Having read the SMI fix wiki, it's not clear how I should go about compiling it for a RIP environment on a custom kernel.

You don't need to, it is a part of realtime code not the kernel
You should find it already compiled in /usr/realtime/modules (or at least it will be in the deb you downloaded for my 3.5.7-rtai, I don't know what is in Sebs packages)

I know nothing about hardware stepping - is that a solution that will run on ANY old PC that can run LinuxCNC?

Pretty much, so long as you have a decent servo thread.

One of Peters Mesa boards (might be one main card and a daughter card, I am not very au fait on them) or Jon Elsons Pico boards
will provide hardware generated pulses independent of the PC, leaving it free to do the interpreter bit etc
It also will provide hugely increased I/O connections, breaking the 17 pins per parport limit.
The only downside is increased cost
www.mesanet.com/fpgacardinfo.html
pico-systems.com/

regards

...and why don't I use them (your next question possibly)

Only because thus far I have been able to get software stepping to work well enough for my requirements, though the use of low latency computers and designer rtai kernels.

Michael H laughs at me compiling custom kernels and running P4s, when I could just add FPGA card and spend the time on something else.

But each to their own, I have become boringly familiar with all aspects of kernel, realtime and linuxcnc compilation in the process and my hardware is never going to stop working for lack of a suitable
rtai system at least

ArcEye wrote:

You should find it already compiled in /usr/realtime/modules

Oh yes, so it is...DUH.

Where is rtapi.conf? "find / -name *rtapi.conf*" finds nothing. Or is there some other way to make the SMI module load?

EDIT:
Yeah, I can see the benefits of hardware stepping but I'm too far into the build to be considering rewiring, however it's certainly something to consider for future builds.

I'm now running Seb's 3.4.55 kernel with the SMI fix enabled (it is loading OK according to lsmod but appears to be unused) and still getting 25K max latency.

BIOS is fully optimized and I've disabled all unused services using rcconf. Results are the same with all my graphics cards and there's not much difference between using PS2 or USB mouse/keyboard. I'm pretty much out of options!

Only other question is regarding IRQ's in BIOS. I notice there's a page that sets the IRQ's for VGA, USB, Network, SATA and Audio. Options are: IRQ5, IRQ10, IRQ11 and Disable. I've set audio to disable but am wondering if there are some conflicts as the default settings put VGA and Network on IRQ5 and then use IRQ10 and IRQ11 for the USB ports and SATA. Is there any mileage to be had here or am I clutching at straws?

Also, HDD is SATA rather than IDE. I don't think it causes any issues, but thought I'd mention it just in case...

EDIT:
Yeah, I can see the benefits of hardware stepping but I'm too far into the build to be considering rewiring, however it's certainly something to consider for future builds.

Actually you can mimic any parallel port pinout with any of the MESA's 25 pin FPGA
cards and there are 3 standard pinouts for parallel port breakouts.

Only other question is regarding IRQ's in BIOS. I notice there's a page that sets the IRQ's for VGA, USB, Network, SATA and Audio. Options are: IRQ5, IRQ10, IRQ11 and Disable. I've set audio to disable but am wondering if there are some conflicts as the default settings put VGA and Network on IRQ5 and then use IRQ10 and IRQ11 for the USB ports and SATA. Is there any mileage to be had here or am I clutching at straws?

You can but try.
I haven't had to change IRQs for years, since the days when some cards were flakey and if you let IRQs be allocated automatically, they conflicted with other cards.

You could even disable the network and see if it has any effect, since it is easy to reinstate when you need it.

There is probably a T junction ahead, one way is signposted 'FPGA' and the other 'Rewind & Try Again'

regards

I've now installed LinuxCNC Ubuntu 8.04 just to prove whether or not this DC7600 is a lemon. Latency started out at 38K with default install. With all BIOS mods (power management disabled, audio disabled, HT disabled,etc) and all unused services and power management disabled in OS, it's now 28K under heavy loading. As mentioned previously (with the Debian Wheezy 3.5.7 UP kernel), it'll sit at around 6.5K with no loading. Graphics seem to be the issue because the spike will occur when launching glxgears or firefox. I'll test with the Matrox card when it arrives. Beyond that, I'll write this PC off as another poor candidate.

On the plus side, my old AMD K8 rig runs at about 16K with the Radeon AGP cards, so is usable. Fingers crossed, the Matrox will improve the latency.

If all else fails, I'll probably splash £50 on a Gigabyte E350N with the AMD cpu as they are reported as giving <5K latency.

The Beaglebone Black is tempting but looks very experimental and I'm not ready for another learning curve (yet)...

I can second the issue with the DC7600. I picked up a pair of them cheap last year from the ex-government auctions and had a play with them. I wasn't able to get the stated latency performance from them. This all became irrelevant, as I went down the Mesa 5i25/7i76 path.

While trying different PCs, I did jag a nice one - an ACER 5900pro with a jitter of 5000 - 6000. Boy this PC was rock-solid, even without a separate graphics card or anything fancy. I listed the results on the Latency Test Wiki, but mistakenly listed it as an ASUS and later couldn't work out how to fix it. I didn't use it in the end as the chassis was too big for the space I had in the cabinet.

Anyway, best of luck with the 'jitters'.

Steve

While trying different PCs, I did jag a nice one - an ACER 5900pro with a jitter of 5000 - 6000. Boy this PC was rock-solid, even without a separate graphics card or anything fancy. I listed the results on the Latency Test Wiki, but mistakenly listed it as an ASUS and later couldn't work out how to fix it.

I have edited your entry and moved the whole database back into something approximating alphabetical order.