choosing hardware

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07 Apr 2009 08:20 - 07 Apr 2009 16:50 #55 by luminize
choosing hardware was created by luminize
Hi guys,

I've installed EMC/Ubuntu on an old computer (P4, 2,6GHz, 1GB ram, 5 years old) and can't run 'latency-test'. I'm getting some segmentation fault and the keyboard input didn't work anymore.
luminize@lumi-P4:~$ latency-test
/etc/init.d/realtime: line 148:  5688 Segmentation fault      $INSMOD $MOD
RTAPI: ERROR: could not open shared memory (errno=2)
HAL: ERROR: rtapi init failed
halcmd: hal_init() failed: -9
NOTE: 'rtapi' kernel module must be loaded
RTAPI: ERROR: could not open shared memory (errno=2)
HAL: ERROR: rtapi init failed
halcmd: hal_init() failed: -9
NOTE: 'rtapi' kernel module must be loaded
RTAPI: ERROR: could not open shared memory (errno=2)
HAL: ERROR: rtapi init failed
halcmd: hal_init() failed: -9
NOTE: 'rtapi' kernel module must be loaded
ERROR: Module hal_lib does not exist in /proc/modules
ERROR: Module rtapi does not exist in /proc/modules
ERROR: Module rtai_math does not exist in /proc/modules
ERROR: Module rtai_sem does not exist in /proc/modules
ERROR: Module rtai_fifos does not exist in /proc/modules
ERROR: Module rtai_sched does not exist in /proc/modules
ERROR: Module rtai_hal is in use
luminize@lumi-P4:~$
So.....
I dug up an old P3 (667Mhz, 385MB ram, about 8 years old) and latency test ran, but was not very good (max jitter base thread 195712, max jitter servo thread 202572).

For testing and playing around, the P3 works for me now, but i want a good system when i'm going to produce chips.
I've ordered an Mesa 5i20 card (should be here in 2 weeks).
Since every computer you buy is shipped with windows (I'm a windows user, I have to use windows for SolidWorks) and i don't want another OEM windows install, I'm thinking of configuring one.

- Is it worth the trouble to try to get the P4 running (or do you suspect even then the latency is bad, the P3 and P4 are the same brand)
- For a new system, should i look for multi-cores or should i be searching for a single core processor. (If multicores don't add anything, why buy them)
- 64 bit or 32 bit?
- Can the video card be the simpelest (cheapest) version available? or spend 40 euro more for something better.
- Any pitfalls i should know about?
- Is there a big chance on errors in a brand new system?
- What considerations should i take for chosing hardware that is stable and balanced (in respect with the other hardware).

Thanks, Bas
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Last edit: 07 Apr 2009 16:50 by luminize.

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07 Apr 2009 12:25 - 14 Apr 2009 11:28 #56 by BigJohnT
Replied by BigJohnT on topic Re:choosing hardware
My guess was wrong so I removed it... seems like the segfault is the important stuff but that is beyond me...

As for computers I use a P3 for my plasma cutter. I had to put a new hard drive on the P3 just to get EMC to install... On one P4 I had to swap video cards because ubuntu didn't reconize it. Sometimes you have to fiddle with the hardware a bit to get everything to cooperate.

As for mesa 5i20's great stuff. Did you get some way to get from the 5i20 to your hardware? If you ordered a mesa card you will need a 50 pin idc cable as well. If you need general i/o then you need a 7i42ta and the 50 pin cable. EMC 2.3 has some real good sample configurations for mesa cards thanks to Seb. I have a 5i20 in a P4 2.4GHz using Hardy and it works great. Latency <10000.

Hope this helps

John
Last edit: 14 Apr 2009 11:28 by alex_joni. Reason: couldn't resist the typo

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07 Apr 2009 13:40 - 14 Apr 2009 11:29 #57 by luminize
Replied by luminize on topic Re:choosing hardware
Hi John,

Just tried halrun -U before you removed your guess, didn't work, one of the errors: RTAPI: ERROR: could not open shared memory (errno=2). Have a feeling it is the memory.

For the P3, i ran the previous latency from the liveCD, after installing on HD i got to 78405/37475, after disabling power managament in the bios, removing PCI modem, second HD, floppy drive and second CD/DVD i got to 52298/32069. A lot better for testing the system, but i hope i can get it further down.

I ordered 3 50 pin cables/connectors, 2 for using, 1 spare. I didn't buy the 7i42 card becouse most stepper/servo drivers already have optocouler isolated inputs. For the other connections/testing i'll solder myself a few optocouplers.

Going to visit a computer/components store, see what they can tell me about components.

Bas
Last edit: 14 Apr 2009 11:29 by alex_joni. Reason: typo

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14 Apr 2009 06:53 - 14 Apr 2009 11:29 #80 by luminize
Replied by luminize on topic Re:choosing hardware
I had a conversation with a guy from a computer store, and his advice was:
Choose a motherboard with an 'older' processor, there could be bugs for the newest processors because when the motherboard was made, they were not yet available.
Also, if something runs in an old P3 or P4, today, anything should run fine on newer systems.
This makes sense to me.
He couldn't tell me if i should choose AMD or INTEL though, Any suggestions?

Bas
Last edit: 14 Apr 2009 11:29 by alex_joni. Reason: typo

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14 Apr 2009 08:19 - 14 Apr 2009 11:28 #87 by alex_joni
Replied by alex_joni on topic Re:choosing hardware
luminize wrote:

I had a conversation with a guy from a computer store, and his advice was:
Choose a motherboard with an 'older' processor, there could be bugs for the newest processors because when the motherboard was made, they were not yet available.
Also, if something runs in an old P3 or P4, today, anything should run fine on newer systems.
This makes sense to me.
He couldn't tell me if i should choose AMD or INTEL though, Any suggestions?

Bas


Both can be equally bad or good (depending on how much luck you have) ;)
I have an AMD Athlon XP 1600+ which works great (needless to say it's quite old).
Also Intel P3's are known to be pretty good with respect to latency. So are some recent Core 2 Duo's (but the chance it works great/doesn't work at all is more pronounced on these).

Take a look at some submitted numbers: wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Latency-Test

Regards,
Alex
Last edit: 14 Apr 2009 11:28 by alex_joni. Reason: chooooosing

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08 Dec 2009 06:52 #1270 by Nick
Replied by Nick on topic Re:choosing hardware
I have the same problem:
When I run invoke.rc-d realtime load
I get: Segmentation fault at line 148.

It happens on Ubuntu 8.04 version both installed and run from LiveCD.
Interesting that 6.06 seems to be working fine. And that I have installed EMC at the same computer about a year ago, then I have rebuilt the kernel, and installed it by myself and it worked fine.

What can cause this problem?

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10 Dec 2009 19:26 #1299 by Tim.G
Replied by Tim.G on topic Re:choosing hardware
I had some trouble installing from the LiveCD, I suspect it had something to do with drivers and/or other hardware incompatabilities.
After installing 8.04 from the Ubuntu distro, updating all the drivers, compiling LinuxCNC on the target system and installing it, all the problems disappeared.
It requires a bit of Linux skill and research though.

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