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Old 02-20-2012, 11:39 AM   #181
theNbomr
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Quote:
Originally Posted by schmitta View Post
The only thing I feel I need to mention is that I think fieldbus implies eithernet
I use the term fieldbus to refer generically to the communication bus and wiring of any protocol and form factor. This is common usage in control systems vernacular.
--- rod.
 
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Old 02-20-2012, 12:30 PM   #182
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I need to keep costs down so I would do the single wire bus over the one cat5 cable.
 
Old 02-20-2012, 12:40 PM   #183
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3k feet of cat5/6 at the lower baud rates (38k) probably will need good foil shielded cat cable, and a good amplifier to send that signal 3k feet. the cost for a good amplifier to drive that signal 3k feet might be a costly item. so i guess the question is, which signal transmission method can get 38k baud across 3k feet of copper w/o mucking up the signal.

btw, what happens if the signal does get messed up along the way, can there be a catastrophic outcome?
 
Old 02-23-2012, 02:26 AM   #184
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Embedded Linux Confrence slides and talks can be found at https://events.linuxfoundation.org/e...ference/slides and http://video.linux.com/categories/20...nux-conference
 
Old 03-02-2012, 06:49 AM   #185
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This is more of a newbie question more than anything. I purchased a Dell Latitude D830 surplus from Virginia Tech for $85. It has a 2.5 GHz processor with 4GB storage. They keep the hard disk so I replaced it with a 160 GB 7200 rpm drive. Thru trial and error I have come up with the following allocations for installing Ubuntu. I partitioned the drive as follows: 1) 100MB for /boot. 2) 8 GB for /swap. 3) 10 GB for / . 4) 141.9 GB for /home. I did this in order to be able to replace the OS with a newer version when they come out without impacting my personal or document files. This is where I need your expertise. Any comments or suggestions you have would be greatly appreciated.

Last edited by schmitta; 03-02-2012 at 06:51 AM.
 
Old 03-02-2012, 11:17 AM   #186
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Looks about right to me.
Quote:
It has a 2.5 GHz processor with 4GB storage.
I assume you mean 4GB RAM. 'Storage' is usually intended to mean some form of disk or other non-volatile media.
--- rod.
 
Old 03-04-2012, 09:31 PM   #187
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I am using the above dell laptop with the above partition setup. I have been experiencing the pointer locking up which I guess is a problem with the GUI (GNOME? UBUNTU). It has even locked up as I am typing this. Could this be because 10 GB is too little space for root? This did not happen when I allowed Ubuntu to allocate space on the disk (just 6GB swap and the rest of the disk for the rest of Ubuntu.) Ubuntu seems to have a question / problem page as part of the distribution. I submitted one question on it but have not checked back to see if it was answered (another problem). I have had various problems with other distributions on other machines, Ubuntu having the least problems. After seeing these problems I marveled that windows never seems to have a problem no matter what machine I load it on (XP and W7). All the people who submit drivers probably have to adhere to strict rules and things probably have not changed since the DOS days. This is probably one of the reasons why Linux (or its distributions) have not caught on more in the world wide community (apple has a much larger base than Linux -- Linux base is tiny). Is it because there is no coordination between distributions? The kernel seems to have its act together in this so maybe the distributions should be controlled by one group with one top guy. It is the only reason I can think of why windows works where as Linux does not on many machines.

Last edited by schmitta; 03-05-2012 at 05:32 PM.
 
Old 03-05-2012, 06:34 PM   #188
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Linux support for laptops is often sketchy because manufacturers use non-standard and undocumented hardware and firmware. They write drivers for Windows, but not for Linux, and the only support is from reverse engineered Windows drivers implemented for Linux by people who are able to do so. Often, there is no way to know exactly how to do things correctly, so support is either incomplete or incorrect. It is a sad fact of life, and is the reason why I expect to have to try numerous Linux distros on any laptop before I find the optimal one, and even then it often isn't complete. Usually, the problems are with less prominent aspects, such as certain kinds of IO (wireless, bluetooth, sound, etc.), but video is another common trouble spot.

--- rod.
 
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Old 04-14-2012, 12:27 AM   #189
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I am considering writing my own isam flat file database for my saved records and information instead of using MySQL. It looks like I will be using the BeagleBone ARM platform for my embedded Linux project. They use OpenEmbedded project for creating the kernel and openembedded no longer supports apache or mysql. They have lighttpd and sqlite3 which are smaller. I am researching ISAM under linux or maybe just making my own. Probably doing this more for fun than anything else.
 
Old 05-08-2012, 02:05 AM   #190
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At this point I am considering not using an SDCARD but using instead a hard disk (2.5 inch laptop disk with USB connection) since the log files alone would probably destroy the SDCARD. Then some system such as Damn Small Linux (50MB) could be used if I can compile it for an arm board. This would increase cost but simplify building the system and the design and coding phase. What do you think?
 
Old 05-08-2012, 04:59 AM   #191
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better used SSD "disk". otherwise you'll be dealing with failed/corrupt drives more often then you would like to. the increase in cost for SSD (con) is trumped by the benefits (pros). in the end the speed/reliability/stability/mtbf all go up.
 
Old 05-08-2012, 08:21 AM   #192
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Depends on how many units you intend to produce. I strongly believe in separation of the target product from the development environment. Using the Arm target as a development host will probably be too slow for a productive development scenario. If you need to replicate a disk image for every unit that you produce, your production cost will be considerably higher with spinning media.
I also think that the write-cycle damage to flash media is heavily over-played. Have you heard of actual damage to SD flash media from this cause? I suggest you take a few SD flash cards of a modest size and try to deliberately destroy them this way. I have done such a test, and was unable to cause even a single failure after exceeding the manufacturer's write-cycle limit by a factor of ten. This was some years ago, when flash memory technology was in its infancy, and the recommended write-cycle limit was 100,000 writes, and the devices did not have built-in wear leveling technology. High capacity flash memory media further reduces the impact, by allowing wear-leveling to be spread out over more memory cells. Modern filesystems further mitigate bad-sector problems. The same technology is used for SSDs as is used in SD flash cards. These seem to be robust enough for use as primary storage in desktop computer systems.
SD flash media can be easily replaced by the end user in the event of failure, but I doubt that you want most end-users to be replacing hard disks. Shipping hard disks is much more expensive than shipping flash media, and shipping units with hard disks installed will be similarly more expensive. Shipping original units with spare flash media seems like a quite reasonable proposition, but I doubt you would want to do the same with any spinning media.

That's what I think.

--- rod.
 
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Old 05-08-2012, 12:20 PM   #193
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If the sdcard fails it would be really bad for the system as the user would have trouble easily accessing the mist controller device units (their address is 7 hex bytes from a silicon serial number chip). One of the benefits of the linux frontend is address translation to human readable unit names. I am considering uploading the day's information to a dedicated server at night so that if they do loose a sdcard they could put a new one in and press a button and be up to speed once again. Thank you for your input it is greatly appreciated. Alvin...
 
Old 05-08-2012, 12:24 PM   #194
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How does the failure of the SD Flash card differ from the failure of a hard disk (other than there being a much simpler remedy)?

--- rod.
 
Old 09-22-2012, 02:20 PM   #195
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There is a new automation for PHP generation. It can be found at: http://cakephp.org/
 
  


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