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• A switch and router between the printer and PC that want to print but cannot

  - by Robert Memo

  IP 192.168.1.5 has a wireless connection to a Linksys router (192.168.1.1) which then is connected to a switch. The switch is connected to a server (192.168.0.2). My printer has IP address of 192.168.0.8. Internet connection is fine on 192.168.1.5. Problem 1: IP 192.168.1.5 can not print using printer 192.168.0.8. Problem 2: IP 192.168.1.2 can not access a shared folder on the the server. The reason for connecting this way is that, the server does not release wireless signal. In order to get wireless signal the Router is connected to the switch. The server is a computer server that only has one outgoing LAN port. Plus, due to inconvinience physical locations, I do not have option to change the physical locations and the way it is connected already. I just want the labtops that only have wireless connection to communicate with the printer and the server. I have tried to change the router IP address to 192.168.0.x like the server and printer. It caused problem for the laptop. The router no longer release internet signals. The router does have IP address from the server 192.168.0.5.

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• Why just splitting an Ethernet cable does not work?

  - by Sin Jeong-hun

  I thought the Ethernet is logically one-line communication bus (for argument's sake, I am excluding hubs). All machines attached in the bus hears the same signals and the machines themselves try to avoid collisions by randomly backing off. http://computer.howstuffworks.com/ethernet6.htm If so, why splitting one Ethernet line from my home router into two and connecting two computers would not work? Why do I have to add a switch to it? *What the Internet said would not work. [4 port home router] ------[one Ethernet cable]-----[simple splitter]======[two computers] *What the Internet said I should do [4 port home router] ------[one Ethernet cable]-----[switch]======[two computers] Is this because of the signal degradation (reduced electric current)? Thank you for all the answers! The reason why I did not just use the two ports of my home router is... The 4-port gigabit router is in my room and I had put a computer in another room (also my room, though). Since wired network is far more reliable and secure, I had bought a long Ethernet cable and and connected the computer to the router. Now I was thinking about adding another computer to that room. I could buy another long Ethernet cable, but then there will be two cables between the rooms. The one line already is a minor annoyance, so I thought if I could share the one line between the two computers in that room. A switch would work, but it requires power and is a little bit pricey. That is why I wondered why it would not work to simply split the physical Ethernet cable. Apparently I do not completely understand how Ethernet and a switch work. I just have some bit of knowledge I heard in my college class.

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• Wifi antenna extension with F-connector/RG-6(RG-59) cable?

  - by rjz2000

  In an older house, the wire mesh in walls surrounding the furnace behave like a Faraday cage and block wifi signals. It is also difficult to lay new cable, however there is television cable to multiple locations due to there once having been a roof-installed, television antenna. It would be relatively trivial to install the wifi router at the center distribution point, then have the antenna broadcasting/receiving the signal plugged in at each of the old television outlets. I assume that it would not be too difficult to find an adapter for SMA <- F-type connectors. The cable is actually RG-59 rather than RG-6, but I assume that it still has relatively good RF isolation along its length, which is no more than a couple hundred feet in any direction. Does anyone know a problem with the idea? Will a router get confused if there is /too little/ interference between the two antenna? Is that length of cable (~100ft) too long for the signal a router broadcasts? I have seen that it is also possible to use old ~$30/each FiOS cable modems available on eBay to extend a network over television cable. However, that seems like a less elegant solution, and might interfere with upnp and dlna services I'd like to have work on a single network. Thanks if anyone has answers or suggestions before I try this project!

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• External HDD connecting via USB disconnects wireless LAN connection

  - by Kensai

  Strange problem. I have this MEDION Akoya PC that has a dedicated bay to slide an external HDD sold separately. It's very handy indeed cause the slot is providing a fast USB 3 connection and power to the HDD unit, without extra cables. All works fine except this show-stopper behavior to disconnect me from the router once I slide in the unit and it powers up. The moment I connect the unit the (normally) three-four WiFi connections I see in my neighborhood disappear and my own to the router loses its signal strength (no Internet traffic is possible). After a while it throws me off that one as well, never to connect me again as long as the unit is powered. Once I disconnect the HDD the various signals come back and it automatically reconnects to my own. What takes? Are we in front of a serious design fault by MEDION here? Does the spinning of the HDD on top of the PC cause electromagnetic interference strong enough to throw off my WiFi connectivity? Is it a simple USB problem? Some kind of strange hardware conflict? Where should I look?

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• Dealing with external processes

  - by Jesse Aldridge

  I've been working on a gui app that needs to manage external processes. Working with external processes leads to a lot of issues that can make a programmer's life difficult. I feel like maintenence on this app is taking an unacceptably long time. I've been trying to list the things that make working with external processes difficult so that I can come up with ways of mitigating the pain. This kind of turned into a rant which I thought I'd post here in order to get some feedback and to provide some guidance to anybody thinking about sailing into these very murky waters. Here's what I've got so far: Output from the child can get mixed up with output from the parent. This can make both outputs misleading and hard to read. It can be hard to tell what came from where. It becomes harder to figure out what's going on when things are asynchronous. Here's a contrived example: import textwrap, os, time from subprocess import Popen test_path = 'test_file.py' with open(test_path, 'w') as file: file.write(textwrap.dedent(''' import time for i in range(3): print 'Hello %i' % i time.sleep(1)''')) proc = Popen('python -B "%s"' % test_path) for i in range(3): print 'Hello %i' % i time.sleep(1) os.remove(test_path) I guess I could have the child process write its output to a file. But it can be annoying to have to open up a file every time I want to see the result of a print statement. If I have code for the child process I could add a label, something like print 'child: Hello %i', but it can be annoying to do that for every print. And it adds some noise to the output. And of course I can't do it if I don't have access to the code. I could manually manage the process output. But then you open up a huge can of worms with threads and polling and stuff like that. A simple solution is to treat processes like synchronous functions, that is, no further code executes until the process completes. In other words, make the process block. But that doesn't work if you're building a gui app. Which brings me to the next problem... Blocking processes cause the gui to become unresponsive. import textwrap, sys, os from subprocess import Popen from PyQt4.QtGui import * from PyQt4.QtCore import * test_path = 'test_file.py' with open(test_path, 'w') as file: file.write(textwrap.dedent(''' import time for i in range(3): print 'Hello %i' % i time.sleep(1)''')) app = QApplication(sys.argv) button = QPushButton('Launch process') def launch_proc(): # Can't move the window until process completes proc = Popen('python -B "%s"' % test_path) proc.communicate() button.connect(button, SIGNAL('clicked()'), launch_proc) button.show() app.exec_() os.remove(test_path) Qt provides a process wrapper of its own called QProcess which can help with this. You can connect functions to signals to capture output relatively easily. This is what I'm currently using. But I'm finding that all these signals behave suspiciously like goto statements and can lead to spaghetti code. I think I want to get sort-of blocking behavior by having the 'finished' signal from QProcess call a function containing all the code that comes after the process call. I think that should work but I'm still a bit fuzzy on the details... Stack traces get interrupted when you go from the child process back to the parent process. If a normal function screws up, you get a nice complete stack trace with filenames and line numbers. If a subprocess screws up, you'll be lucky if you get any output at all. You end up having to do a lot more detective work everytime something goes wrong. Speaking of which, output has a way of disappearing when dealing external processes. Like if you run something via the windows 'cmd' command, the console will pop up, execute the code, and then disappear before you have a chance to see the output. You have to pass the /k flag to make it stick around. Similar issues seem to crop up all the time. I suppose both problems 3 and 4 have the same root cause: no exception handling. Exception handling is meant to be used with functions, it doesn't work with processes. Maybe there's some way to get something like exception handling for processes? I guess that's what stderr is for? But dealing with two different streams can be annoying in itself. Maybe I should look into this more... Processes can hang and stick around in the background without you realizing it. So you end up yelling at your computer cuz it's going so slow until you finally bring up your task manager and see 30 instances of the same process hanging out in the background. Also, hanging background processes can interefere with other instances of the process in various fun ways, such as causing permissions errors by holding a handle to a file or someting like that. It seems like an easy solution to this would be to have the parent process kill the child process on exit if the child process didn't close itself. But if the parent process crashes, cleanup code might not get called and the child can be left hanging. Also, if the parent waits for the child to complete, and the child is in an infinite loop or something, you can end up with two hanging processes. This problem can tie in to problem 2 for extra fun, causing your gui to stop responding entirely and force you to kill everything with the task manager. F***ing quotes Parameters often need to be passed to processes. This is a headache in itself. Especially if you're dealing with file paths. Say... 'C:/My Documents/whatever/'. If you don't have quotes, the string will often be split at the space and interpreted as two arguments. If you need nested quotes you can use ' and ". But if you need to use more than two layers of quotes, you have to do some nasty escaping, for example: "cmd /k 'python \'path 1\' \'path 2\''". A good solution to this problem is passing parameters as a list rather than as a single string. Subprocess allows you to do this. Can't easily return data from a subprocess. You can use stdout of course. But what if you want to throw a print in there for debugging purposes? That's gonna screw up the parent if it's expecting output formatted a certain way. In functions you can print one string and return another and everything works just fine. Obscure command-line flags and a crappy terminal based help system. These are problems I often run into when using os level apps. Like the /k flag I mentioned, for holding a cmd window open, who's idea was that? Unix apps don't tend to be much friendlier in this regard. Hopefully you can use google or StackOverflow to find the answer you need. But if not, you've got a lot of boring reading and frusterating trial and error to do. External factors. This one's kind of fuzzy. But when you leave the relatively sheltered harbor of your own scripts to deal with external processes you find yourself having to deal with the "outside world" to a much greater extent. And that's a scary place. All sorts of things can go wrong. Just to give a random example: the cwd in which a process is run can modify it's behavior. There are probably other issues, but those are the ones I've written down so far. Any other snags you'd like to add? Any suggestions for dealing with these problems?

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• resizing row's height in QTreeWidget/QTreeView

  - by serge

  Hi everyone, I have some problems with sizing row's height in QTreeWidget. I use QStyledItemDelegate with QPlainTextEdit. During editing text in QPlainTextEdit i check for changes with a help of: rect = self.blockBoundingRect(self.firstVisibleBlock()) and if text's height changes i resize editor size and need row in QTreeWidget also resizing. But i don't know how to inform TreeWidget or a Delegate about changes. I tried to initialize editor with index, that i could use in a future, but Delegate creates new editor every time and i failed to use signals. Also I used following function to catch resize event, but it' doesn't: bool QAbstractItemDelegate::editorEvent ( QEvent * event, QAbstractItemModel * model, const QStyleOptionViewItem & option, const QModelIndex & index ) How can i bound editor's size changes with TreeWidget? And one more thing, by default all items (cells) in TreeWidget have -1 or some big value as default width. I need whole text in cell to be visible, so how can i limit cells width only by visible range and make it expand in height? I want for it the same behavior as in instance a table in MSWord. Thank you in advance, Serge

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• Using QTDesigner with PyQT and Python 2.6

  - by PyNewbie27

  Hi. I'm fairly new to Python and trying to work with the latest versions of QTDesigner, PyQT 4.7 and QT4.7 (I downloaded the whole package from PyQT4.7 website). I can't figure out how to make QTDesigner integrate closely with Python: ie. If I select "Form" View Code in QTDesigners menu, it errors saying "Unable to launch C:/Python26/Lib/site-packages/PyQT4/bin\uic." If I look in that directory there is a pyuic.py but not "uic". From searching online it seems this doesn't exist because it's expecting a C++ install instead of the python version. Is there anyway to make QTDesigner use/call pyuic.py to generate the code, then open an IDE or text editor of my choice to show me the PYTHON code generated by the QTDesigner-PyUIC chain? I'd like Designer to integrate closely with python, so I can make custom slots/signals in Designer while designing, then tweak the python code directly in my IDE later. If it is not possible to code directly inside QTDesigner using python, does that mean I have to hand code my programs entire UI directly in my PythonIDE? Using Designer directly would seemingly be nearly very very nice for a newbie such as myself, since I can see what properties each widget has and visually edit them while still learning the QT syntax without constantly having to use web resources to see what properties each widget should have and helps with boilerplate code generation, and what their defaults are, etc. I've googled and nobody seems to be using QTDesigner and Python in this manner together. It seems most are either handcoding all the QT code in their Python IDE of choice, or have found an obvious/easy method of doing what I want, therefore not really producing up to date tutorials on making this work together. Please enlighten me if you can. Thanks in advance for your time. Please include any suggestions you might have to a newbie trying to use Python with QT and QTDesigner. Thank you.

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• django: error while migrating from 1.1 to 1.2

  - by gruszczy

  I am trying to migrate our django project from 1.1 to 1.2, but I get following error: Traceback (most recent call last): File "./manage.py", line 11, in <module> execute_manager(settings) File "/usr/local/lib/python2.6/dist-packages/django/core/management/__init__.py", line 438, in execute_manager utility.execute() File "/usr/local/lib/python2.6/dist-packages/django/core/management/__init__.py", line 379, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File "/usr/local/lib/python2.6/dist-packages/django/core/management/base.py", line 191, in run_from_argv self.execute(*args, **options.__dict__) File "/usr/local/lib/python2.6/dist-packages/django/core/management/base.py", line 209, in execute translation.activate('en-us') File "/usr/local/lib/python2.6/dist-packages/django/utils/translation/__init__.py", line 66, in activate return real_activate(language) File "/usr/local/lib/python2.6/dist-packages/django/utils/functional.py", line 55, in _curried return _curried_func(*(args+moreargs), **dict(kwargs, **morekwargs)) File "/usr/local/lib/python2.6/dist-packages/django/utils/translation/__init__.py", line 36, in delayed_loader return getattr(trans, real_name)(*args, **kwargs) File "/usr/local/lib/python2.6/dist-packages/django/utils/translation/trans_real.py", line 193, in activate _active[currentThread()] = translation(language) File "/usr/local/lib/python2.6/dist-packages/django/utils/translation/trans_real.py", line 176, in translation default_translation = _fetch(settings.LANGUAGE_CODE) File "/usr/local/lib/python2.6/dist-packages/django/utils/translation/trans_real.py", line 159, in _fetch app = import_module(appname) File "/usr/local/lib/python2.6/dist-packages/django/utils/importlib.py", line 35, in import_module __import__(name) File "/home/gruszczy/Programy/bozorth/../bozorth/notifications/__init__.py", line 2, in <module> from django.db.models.signals import post_save File "/usr/local/lib/python2.6/dist-packages/django/db/__init__.py", line 75, in <module> connection = connections[DEFAULT_DB_ALIAS] File "/usr/local/lib/python2.6/dist-packages/django/db/utils.py", line 92, in __getitem__ conn = backend.DatabaseWrapper(db, alias) File "/usr/local/lib/python2.6/dist-packages/django/db/backends/sqlite3/base.py", line 154, in __init__ super(DatabaseWrapper, self).__init__(*args, **kwargs) TypeError: __init__() takes exactly 2 arguments (3 given) Anyone encountered this problem and know, how to solve?

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• Home automation using Arduino / XMPP client for Arduino

  - by Ashish

  I am trying to setup a system for automating certain tasks in my home. I am thinking of a solution wherein a server side application would be able to send/receive commands/data to Arduino (attached with Arduino Ethernet Shield) via the web. Here the Arduino may both act as a sensor interface to the server application or command executor interface for the server app. E.g. (user story): The overhead water tank in my house has a water level sensor attached with Arduino (attached with Arduino Ethernet Shield). Another Arduino (attached with Arduino Ethernet Shield) is attached with a relay/latch. This relay/latch is then connected to a water pump. Now the server side application on the web is able to get/receive water level information from the Arduino on the water tank. Depending on the water level information received, the web application should send suitable signals/commands to Arduino on water pump to switch 'ON' or switch 'OFF' the water pump. Now for such a system to work across the web, I am thinking of using one of the type of solutions in order of my priority: Using XMPP for communication between server application and Arduino. Using HTTP polling. Using HTTP hanging GET. For solution number 1, I need to implement a XMPP client that would reside on Arduino. Is it possible to write a XMPP client small enough to reside on an Arduino? If yes what are the minimum possible XMPP client functionality that I need to write for Arduino, so that it would be able to contact XMPP servers solutions like GTalk, etc.? For solution number 2 and 3 I need guidance in implementation. Also which solution would be cost effective and easily extendable?

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• Need help with artificial neural network

  - by deckard cain

  I have an input data for neural network that consists of 2 vectors with 200 elements, that i got from some program for generating signals. So it is actually 2x200 input to my nnet. As target data, i have one 1x200 vector that i also got from the same program. That is my training data set. I gather as much of those sets as i want so i transfer them to matlab and save them as, for example, set1, set2,.... When i am creating neural net, using newfit function (backropagation algorithm and everyhting else is set by default because i am kind of unexperianced with neural nets so i will have to experiment) i'm creating it using set1 only for example. Then, when i am to train neural net i train it for set1 then load set2 and train for it and so on. so its like this function net = create_fit_net(inputs,targets) numHiddenNeurons = 20; net = newfit(inputs,targets,numHiddenNeurons); net=train(net,inputs,targets); load set2; net=train(net,inputs,targets); load set3; net=train(net,inputs,targets); load set4; net=train(net,inputs,targets); i am using 4 sets of data here and all sets have variables of same name and size. My quesion is, am i doing this the right way, because, when doing simulation in some other m file, i am getting bad results, and every time i get different results. Does it matter if i create network with one set and then train with others too, and does it matter what set do i use to train network 1st? Also, i am confused about the amount of neurons to use (im using in the example 20 but actually i tried 1, 10, 30, 50, 100 200 and even 300 and i get nothing). If you have any suggestions, i'd be glad to take them into consideration. Any help is welcome. thanks in advance

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• Developing a GPS car tracking system in C#

  - by Click Ok

  I'm in the brainstorming phase to develop a GPS car tracking system requested by a customer. I myself know the directions to build some GPS system to mobile phones and etc. But sincerely I don't know how to start in that project. That is the scenario: 1) The cars will get a device with a SIM CARD that will emit GPS signals. 2) My customer will in any place (home, work, etc) with a web connection will see in the map where the car is located. For me, I have not problems at get the GPS data, convert to usable info and show the position in some map system (like Google Maps or MS Bing Maps, by example). My problem is, how I do to retrieve that "GPS Signal" from device in the car? I will need some kind of "Receiver Device" connected to a web server machine in order to my application to consume that data? Or "automagically" my sodtware will receive the info from a third-party web-service? Or what? I thank for any help!

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• Qt Object Linker Problem " undefined reverence to vtable"

  - by Thomas

  This is my header: #ifndef BARELYSOCKET_H #define BARELYSOCKET_H #include <QObject> //! The First Draw of the BarelySocket! class BarelySocket: public QObject { Q_OBJECT public: BarelySocket(); public slots: void sendMessage(Message aMessage); signals: void reciveMessage(Message aMessage); private: // QVector<Message> reciveMessages; }; #endif // BARELYSOCKET_H This is my class: #include <QTGui> #include <QObject> #include "type.h" #include "client.h" #include "server.h" #include "barelysocket.h" BarelySocket::BarelySocket() { //this->reciveMessages.clear(); qDebug("BarelySocket::BarelySocket()"); } void BarelySocket::sendMessage(Message aMessage) { } void BarelySocket::reciveMessage(Message aMessage) { } I get the Linker Problem : undefined reference to 'vtable for barelySocket' This should mean, i have a virtual Function not implemented. But as you can see, there is non. I comment the vector cause that should solve the Problem, but i does not. The Message is a complex struct, but even converting it to int did not solve it. I searched Mr G but he could not help me. Thank you for your support, Thomas

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• POSIX AIO Library and Callback Handlers

  - by Charles Salvia

  According to the documentation on aio_read/write, there are basically 2 ways that the AIO library can inform your application that an async file I/O operation has completed. Either 1) you can use a signal, 2) you can use a callback function I think that callback functions are vastly preferable to signals, and would probably be much easier to integrate into higher-level multi-threaded libraries. Unfortunately, the documentation for this functionality is a mess to say the least. Some sources, such as the man page for the sigevent struct, indicate that you need to set the sigev_notify data member in the sigevent struct to SIGEV_CALLBACK and then provide a function handler. Presumably, the handler is invoked in the same thread. Other documentation indicates you need to set sigev_notify to SIGEV_THREAD, which will invoke the callback handler in a newly created thread. In any case, on my Linux system (Ubuntu with a 2.6.28 kernel) SIGEV_CALLBACK doesn't seem to be defined anywhere, but SIGEV_THREAD works as advertised. Unfortunately, creating a new thread to invoke the callback handler seems really inefficient, especially if you need to invoke many handlers. It would be better to use an existing pool of threads, similar to the way most network I/O event demultiplexers work. Some versions of UNIX, such as QNX, include a SIGEV_SIGNAL_THREAD flag, which allows you to invoke handlers using a specified existing thread, but this doesn't seem to be available on Linux, nor does it seem to even be a part of the POSIX standard. So, is it possible to use the POSIX AIO library in a way that invokes user handlers in a pre-allocated background thread/threadpool, rather than creating/destroying a new thread everytime a handler is invoked?

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• Debugging MinGW program with gdb on Windows, not terminating at assert failure

  - by devil

  How do I set up gdb on window so that it does not allow a program with assertion failure to terminate? I intend to check the stack trace and variables in the program. For example, running this test.cpp program compiled with MinGW 'g++ -g test.cpp -o test' in gdb: #include <cassert> int main(int argc, char ** argv) { assert(1==2); return 0; } Gives: $ gdb test.exe GNU gdb 6.8 Copyright (C) 2008 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "i686-pc-mingw32"... (gdb) r Starting program: f:\code/test.exe [New thread 4616.0x1200] Error: dll starting at 0x77030000 not found. Error: dll starting at 0x75f80000 not found. Error: dll starting at 0x77030000 not found. Error: dll starting at 0x76f30000 not found. Assertion failed: 1==2, file test.cpp, line 2 This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. Program exited with code 03. (gdb) I would like to be able to stop the program from terminating immediately, like how Visual Studio's debugger and gdb on Linux does it. I have done a search and found some stuff on trapping signals but I can't seem to find a good post on how to set up gdb to do this.

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• Figuring out the performance limitation of an ADC on a PIC microcontroller

  - by AKE

  I'm spec-ing the suitability of a microcontroller like PIC for an analog-to-digital application. This would be preferable to using external A/D chips. To do that, I've had to run through some computations, pulling the relevant parameters from the datasheets. I'm not sure I've got it right -- would appreciate a check! Here's the simplest example: PIC10F220 is the simplest possible PIC with an ADC. Runs at clock speed of 8MHz. Has an instruction cycle of 0.5us (4 clock steps per instruction) So: Taking Tacq = 6.06 us (acquisition time for ADC, assume chip temp. = 50*C) [datasheet p34] Taking Fosc = 8MHz (? clock speed) Taking divisor = 4 (4 clock steps per CPU instruction) This gives TAD = 0.5us (TAD = 1/(Fosc/divisor) ) Conversion time is 13*TAD [datasheet p31] This gives conversion time 6.5us ADC duration is then 12.56 us [? Tacq + 13*TAD] Assuming at least 2 instructions for load/store: This is another 1 us [0.5 us per instruction] Which would give max sampling rate of 73.7 ksps (1/13.56) Supposing 8 more instructions for real-time processing: This is another 4 us Thus, total ADC/handling time = 17.56us (12.56us + 1us + 4us) So expected upper sampling rate is 56.9 ksps. Nyquist frequency for this sampling rate is therefore 28 kHz. If this is right, it suggests the (theoretical) performance suitability of this chip's A/D is for signals that are bandlimited to 28 kHz. Is this a correct interpretation of the information given in the data sheet? Any pointers would be much appreciated! AKE

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• Figuring out the Nyquist performance limitation of an ADC on an example PIC microcontroller

  - by AKE

  I'm spec-ing the suitability of a dsPIC microcontroller for an analog-to-digital application. This would be preferable to using dedicated A/D chips and a separate dedicated DSP chip. To do that, I've had to run through some computations, pulling the relevant parameters from the datasheets. I'm not sure I've got it right -- would appreciate a check! (EDITED NOTE: The PIC10F220 in the example below was selected ONLY to walk through a simple example to check that I'm interpreting Tacq, Fosc, TAD, and divisor correctly in working through this sort of Nyquist analysis. The actual chips I'm considering for the design are the dsPIC33FJ128MC804 (with 16b A/D) or dsPIC30F3014 (with 12b A/D).) A simple example: PIC10F220 is the simplest possible PIC with an ADC Runs at clock speed of 8MHz. Has an instruction cycle of 0.5us (4 clock steps per instruction) So: Taking Tacq = 6.06 us (acquisition time for ADC, assume chip temp. = 50*C) [datasheet p34] Taking Fosc = 8MHz (? clock speed) Taking divisor = 4 (4 clock steps per CPU instruction) This gives TAD = 0.5us (TAD = 1/(Fosc/divisor) ) Conversion time is 13*TAD [datasheet p31] This gives conversion time 6.5us ADC duration is then 12.56 us [? Tacq + 13*TAD] Assuming at least 2 instructions for load/store: This is another 1 us [0.5 us per instruction] Which would give max sampling rate of 73.7 ksps (1/13.56) Supposing 8 more instructions for real-time processing: This is another 4 us Thus, total ADC/handling time = 17.56us (12.56us + 1us + 4us) So expected upper sampling rate is 56.9 ksps. Nyquist frequency for this sampling rate is therefore 28 kHz. If this is right, it suggests the (theoretical) performance suitability of this chip's A/D is for signals that are bandlimited to 28 kHz. Is this a correct interpretation of the information given in the data sheet in obtaining the Nyquist performance limit? Any opinions on the noise susceptibility of ADCs in PIC / dsPIC chips would be much appreciated! AKE

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• Is it possible that a single-threaded program is executed simultaneously on more than one CPU core?

  - by Wolfgang Plaschg

  When I run a single-threaded program that i have written on my quad core Intel i can see in the Windows Task Manager that actually all four cores of my CPU are more or less active. One core is more active than the other three, but there is also activity on those. There's no other program (besided the OS kernel of course) running that would be plausible for that activitiy. And when I close my program all activity an all cores drops down to nearly zero. All is left is a little "noise" on the cores, so I'm pretty sure all the visible activity comes directly or indirectly (like invoking system routines) from my program. Is it possible that the OS or the cores themselves try to balance some code or execution on all four cores, even it's not a multithreaded program? Do you have any links that documents this technique? Some infos to the program: It's a console app written in Qt, the Task Manager states that only one thread is running. Maybe Qt uses threads, but I don't use signals or slots, nor any GUI. Link to Task Manager screenshot: http://img97.imageshack.us/img97/6403/taskmanager.png This question is language agnostic and not tied to Qt/C++, i just want to know if Windows or Intel do to balance also single-threaded code on all cores. If they do, how does this technique work? All I can think of is, that kernel routines like reading from disk etc. is scheduled on all cores, but this won't improve performance significantly since the code still has to run synchronous to the kernel api calls. EDIT Do you know any tools to do a better analysis of single and/or multi-threaded programs than the poor Windows Task Manager?

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• Switch statement usage - C

  - by Jamie Keeling

  Hello, I have a thread function on Process B that contains a switch to perform certain operations based on the results of an event sent from Process A, these are stored as two elements in an array. I set the first element to the event which signals when Process A has data to send and I have the second element set to the event which indicates when Process A has closed. I have began to implement the functionality for the switch statement but I'm not getting the results as I expect. Consider the following: // //Thread function DWORD WINAPI ThreadFunc(LPVOID passedHandle) { for(i = 0; i < 2; i++) { ghEvents[i] = OpenEvent(EVENT_ALL_ACCESS, FALSE, TEXT("Global\\ProducerEvents")); if(ghEvents[i] == NULL) { getlasterror = GetLastError(); } } dwProducerEventResult = WaitForMultipleObjects( 2, ghEvents, FALSE, INFINITE); switch (dwProducerEventResult) { case WAIT_OBJECT_0 + 0: { //Producer sent data //unpackedHandle = *((HWND*)passedHandle); MessageBox(NULL,L"Test",L"Test",MB_OK); break; } case WAIT_OBJECT_0 + 1: { //Producer closed ExitProcess(1); break; } default: return; } } As you can see if the event in the first array is signalled Process B should display a simple message box, if the second array is signalled the application should close. When I actually close Process A, Process B displays the message box instead. If I leave the first case blank (Do nothing) both applications close as they should. Furthermore Process B sends data an error is thrown (When I comment out the unpacking): Have I implemented my switch statement incorrectly? I though I handled the unpacking of the HWND correctly too, any suggestions? Thanks for your time.

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• Using pipes in Linux with C

  - by Dave

  Hi, I'm doing a course in Operating Systems and we're supposed to learn how to use pipes to transfer data between processes. We were given this simple piece of code which demonstrates how to use pipes,but I'm having difficulty understanding it. #include <stdio.h> #include <stdlib.h> #include <unistd.h> main() { int pipefd [2], n; char buff[100] ; if( pipe( pipefd) < 0) { printf("can not create pipe \n"); } printf("read fd = %d, write fd = %d \n", pipefd[0], pipefd[1]); if ( write (pipefd[1],"hello world\n", 12)!= 12) { printf("pipe write error \n"); } if( ( n = read ( pipefd[0] , buff, sizeof ( buff) ) ) <= 0 ) { printf("pipe read error \n"); } write ( 1, buff, n ) ; exit (0); } What does the write function do? It seems to send data to the pipe and also print it to the screen (at least it seems like the second time the write function is called it does this). Does anyone have any suggestions of good websites for learning about topics such as this, FIFO, signals, other basic linux commands used in C?

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• Programmatically disable WiredHeadset

  - by tyrone-tudehope

  Hi, I have an HTC Hero with a major issue. It thinks that the headset/headphones are plugged in. I sent it to HTC and they said there is water damage so no fix. I have tried toggleheadset, toggleheadset2. I've rooted my device and installed the Android 2.1 ROM. Now I found out that AudioManager.setRouting and .setWiredHeadsetOn(bool) have been deprecated and subsequently removed. I read a post somewhere about how you can create a wrapper for the AudioSystem class as the setRouting is still available there. I as of yet have not been able to figure out how to go about doing this as the AudioSystem class is hidden in the SDK and the code makes use of native functions. Does anybody know of a way to go about creating and implementing a wrapper for AudioSystem or of another way to disable the headset? P.S. I've cleaned out the headset port so there is no dust or anything sending false signals to the mainboard. Any help will be greatly appreciated. Thanks, Tyrone

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• Django - how to write users and profiles handling in best way?

  - by SpankMe

  Hey, I am writing simple site that requires users and profiles to be handled. The first initial thought is to use django's build in user handling, but then the user model is too narrow and does not contain fields that I need. The documentation mentions user profiles, but user profiles section has been removed from djangobook covering django 1.0 (ideally, the solution should work with django 1.2), and the Internet is full of different solutions, not making the choice easier (like user model inheritance, user profiles and django signals, and so on). I would like to know, how to write this in good, modern, fast and secure way. Should I try to extend django builtin user model, or maybe should I create my own user model wide enough to keep all the information I need? Below you may find some specifications and expectations from the working solution: users should be able to register and authenticate every user should have profile (or model with all required fields) users dont need django builtin admin panel, but they need to edit their profiles/models via simple web form Please, let me know how do you solve those issues in your applications, and what is the best current way to handle users with django. Any links to articles/blogs or code examples are highly appreciated!

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• How to get at contents of placeholder::_1

  - by sheepsimulator

  I currently have the following code: using boost::bind; typedef boost::signal<void(EventDataItem&)> EventDataItemSignal; class EventDataItem { ... EventDataItemSignal OnTrigger; ... } typedef std::list< shared_ptr<EventDataItem> > DataItemList; typedef std::list<boost::signals::connection> ConnectionList; class MyClass { void OnStart() { DataItemList dilItems; ConnectionList clConns; DataItemList::iterator iterDataItems; for(iterDataItems = dilItems.begin(); iterDataItems != dilItems.end(); iterDataItems++) { // Create Connections from Triggers clConns.push_back((*iterDataItems)->OnTrigger.connect( bind(&MyClass::OnEventTrigger, this))); } } void OnEventTrigger() { // ... Do stuff on Trigger... } } I'd like to change MyClass::OnStart to use std::transform to achieve the same thing: void MyClass::OnStart() { DataItemList dilItems; ConnectionList clConns; // Resize connection list to match number of data items clConns.resize(dilItems.size()); // Build connection list from Items // note: errors on the placeholder _1->OnTrigger std::transform(dilItems.begin(), dilItems.end(), clConns.begin(), bind(&EventDataItemSignal::connect, _1->OnTrigger, bind(&MyClass::Stuff, this))); } However, my hiccup is _1-OnTrigger. How can I reference OnTrigger from placeholder _1?

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• SOLVED: Lisp: macro calling a function works in interpreter, fails in compiler (SBCL + CMUCL)

  - by ttsiodras

  As suggested in a macro-related question I recently posted to SO, I coded a macro called "fast" via a call to a function (here is the standalone code in pastebin): (defun main () (progn (format t "~A~%" (+ 1 2 (* 3 4) (+ 5 (- 8 6)))) (format t "~A~%" (fast (+ 1 2 (* 3 4) (+ 5 (- 8 6))))))) This works in the REPL, under both SBCL and CMUCL: $ sbcl This is SBCL 1.0.52, an implementation of ANSI Common Lisp. ... * (load "bug.cl") 22 22 $ Unfortunately, however, the code no longer compiles: $ sbcl This is SBCL 1.0.52, an implementation of ANSI Common Lisp. ... * (compile-file "bug.cl") ... ; during macroexpansion of (FAST (+ 1 2 ...)). Use *BREAK-ON-SIGNALS* to ; intercept: ; ; The function COMMON-LISP-USER::CLONE is undefined. So it seems that by having my macro "fast" call functions ("clone","operation-p") at compile-time, I trigger issues in Lisp compilers (verified in both CMUCL and SBCL). Any ideas on what I am doing wrong and/or how to fix this?

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• How to compare two variables from a java class in jess and execute a rule?

  - by user3417084

  I'm beginner in Jess. I'm trying to compare two variables from a Java class in Jess and trying to execute a rule. I have imported cTNumber and measuredCurrent (both are integer)form a java class called CurrentSignal. Similarly imported vTNumberand measuredVoltage form a java class DERSignal. Now I want to make a rule such that if cTNumber is equal to vTNumber then multiply measuredCurrent and measuredVoltage (Both are double) for calculating power. I'm trying in this way.... (import signals.*) (deftemplate CurrentSignal (declare (from-class CurrentSignal))) (deftemplate DERSignal (declare (from-class DERSignal))) (defglobal ?*CTnumber* = 0) (defglobal ?*VTnumber* = 0) (defglobal ?*VTnumberDER* = 0) (defglobal ?*measuredCurrent* = 0) (defglobal ?*measuredVoltage* = 0) (defglobal ?*measuredVoltageDER* = 0) (defrule Get-CT-Number (CurrentSignal (cTNumber ?m)) (CurrentSignal (measuredCurrent ?c)) => (bind ?*measuredCurrent* ?c) (printout t "Measured Current : " ?*measuredCurrent*" Amps"crlf) (bind ?*CTnumber* ?m) (printout t ?*CTnumber* crlf) ) (defrule Get-DER-Number (DERSignal (vTNumber ?o)) (DERSignal (measuredVoltage ?V)) => (bind ?*measuredVoltageDER* ?V) (printout t "Measured Voltage : " ?*measuredVoltageDER* " V" crlf) (bind ?*VTnumberDER* ?o) (printout t ?*VTnumberDER* crlf) ) (defrule Power-Calculation-DER-signal "Power calculation of DER Bay" (test (= ?*CTnumber* ?*VTnumberDER* )) => (printout t "Total Generation : " (* ?*measuredCurrent* ?*measuredVoltageDER*) crlf) ) But the Total Generation is showing 0. But I tried calculating in Java and it's showing a number. Can anyone please help me to solve this problem. Thank you.

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• How to interrupt a thread performing a blocking socket connect?

  - by Jason R

  I have some code that spawns a pthread that attempts to maintain a socket connection to a remote host. If the connection is ever lost, it attempts to reconnect using a blocking connect() call on its socket. Since the code runs in a separate thread, I don't really care about the fact that it uses the synchronous socket API. That is, until it comes time for my application to exit. I would like to perform some semblance of an orderly shutdown, so I use thread synchronization primitives to wake up the thread and signal for it to exit, then perform a pthread_join() on the thread to wait for it to complete. This works great, unless the thread is in the middle of a connect() call when I command the shutdown. In that case, I have to wait for the connect to time out, which could be a long time. This makes the application appear to take a long time to shut down. What I would like to do is to interrupt the call to connect() in some way. After the call returns, the thread will notice my exit signal and shut down cleanly. Since connect() is a system call, I thought that I might be able to intentionally interrupt it using a signal (thus making the call return EINTR), but I'm not sure if this is a robust method in a POSIX threads environment. Does anyone have any recommendations on how to do this, either using signals or via some other method? As a note, the connect() call is down in some library code that I cannot modify, so changing to a non-blocking socket is not an option.

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