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• OMAP 3530: How fast can I toggle an IO?

  - by raj.tiwari

  I am putting together an application for OMAP 3530 SoC. This application will run some user interface code on embedded linux and invoke waveform generation code on the DSP. The DSP and Linux sides will interact over DSP/BIOS link. My questions are: What is the highest frequency at which my DSP-side code can toggle a GPIO line? If I want to toggle multiple GPIO lines at this hight rate, how fast can I go? Thanks for any insights. -Raj

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• string matching algorithms used by lucene

  - by iamrohitbanga

  i want to know the string matching algorithms used by Apache Lucene. i have been going through the index file format used by lucene given here. it seems that lucene stores all words occurring in the text as is with their frequency of occurrence in each document. but as far as i know that for efficient string matching it would need to preprocess the words occurring in the Documents. example: search for "iamrohitbanga is a user of stackoverflow" (use fuzzy matching) in some documents. it is possible that there is a document containing the string "rohit banga" to find that the substrings rohit and banga are present in the search string, it would use some efficient substring matching. i want to know which algorithm it is. also if it does some preprocessing which function call in the java api triggers it.

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• Normalize FFT magnitude to imitate WMP

  - by Bevin

  So, I've been working on a little visualizer for sound files, just for fun. I basically wanted to imitate the "Scope" and "Ocean Mist" visualizers in Windows Media Player. Scope was easy enough, but I'm having problems with Ocean Mist. I'm pretty sure that it is some kind of frequency spectrum, but when I do an FFT on my waveform data, I'm not getting the data that corresponds to what Ocean Mist displays. The spectrum actually looks correct, so I knew there was nothing wrong with the FFT. I'm assuming that the visualizer runs the spectrum through some kind of filter, but I have no idea what it might be. Any ideas?

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• Are primitive types garbage collected in Android?

  - by snctln

  I know this may be a dumb question, but my background is more in c++ and managing my own memory. I am currently cutting down every single allocation that I can from one of my games to try and reduce the frequency of garbage collection and perceived "lag", so for every variable that I create that is an Object (String and Rect for example) I am making sure that I create it before hand in my constructor and not create temporary variables in simple 10 line functions... (I hope that makes sense) Anyways I was working though it some more tonight and I realized that I may be completely wrong about my assumption on garbage collection and primitive types (int, boolean, float) are these primitive type variables that I create in a 10 line function that gets called 20 times a second adding to my problem of garbage collection? So a year ago every few seconds I would see a message in logcat like GC freed 4010 objects / 484064 bytes in 101ms Now I see that message every 15-90 seconds or so... So to rephrase my question: Are primitive types (int, float, boolean, etc) included when seeing this message?

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• Stripe suppression algorithm needed

  - by maximus

  I have images with text. There are dark stripes in image that still exists in binary image too. That makes characters connected with that stripe - it can be vertical or horizontal (or at some angle) I need to remove them from image at first, and then to binarize. I've seen bandpass filter in ImageJ program that have some options like - suppress horizontal stripes, and it works good, but it also apply a bandpass filtering. So any idea please how to do it. I think it should be done in frequency domain.

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• How to efficiently track my geolocation during traveling using iPhone

  - by Peter Kruithof

  I'm going to travel through Thailand and I want to keep track of my location to geotag photos afterwards taken with a digital camera (iPhone's camera is not good enough). There are two things that are important here: I don't want to update manually I want the battery to last as long as possible, since the times I will be able to charge will be scarce I've thought about creating a web page that periodically sends my geolocation to a script that stores it in a database, but I don't know if GPS data is available in Mobile Safari. Second, I want the data I send to be as small as possible, and the frequency this is done s few as possible, because of the pricing of mobile data usage abroad. Any suggestions what would be a good solution here?

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• typesafe NotifyPropertyChanged using linq expressions

  - by bitbonk

  Form Build your own MVVM I have the following code that lets us have typesafe NotifyOfPropertyChange calls: public void NotifyOfPropertyChange<TProperty>(Expression<Func<TProperty>> property) { var lambda = (LambdaExpression)property; MemberExpression memberExpression; if (lambda.Body is UnaryExpression) { var unaryExpression = (UnaryExpression)lambda.Body; memberExpression = (MemberExpression)unaryExpression.Operand; } else memberExpression = (MemberExpression)lambda.Body; NotifyOfPropertyChange(memberExpression.Member.Name); } How does this approach compare to standard simple strings approach performancewise? Sometimes I have properties that change at a very high frequency. Am I safe to use this typesafe aproach? After some first tests it does seem to make a small difference. How much CPU an memory load does this approach potentially induce?

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• Is it ever a bad idea to publish a sitemap for a blog?

  - by mipadi

  I have a blog, and I have been considering publishing a sitemap for it, which would include the index page, archives page, and an entry for each individual blog post. Is this ever a bad idea? Is it a good (or useful) idea? I'm particularly interested in the <changefreq> element: I edit posts from time to time, and while that's not a common occurrence, I don't want to set a particularly infrequent change frequency that prevents search engines like Google from indexing the edits. (The sitemaps protocol says that search engines may still crawl the pages more frequently, but has no further details on the matter.)

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• Converting a Doc object into a string in python

  - by Sam

  I'm using minidom to parse through an xml document. I took the data with yum tags and stored them in a list and calculated the frequency of the words. However, its not storing or reading them as strings in the list. Is there another way to do it? Right now this is what I have: yumNodes = [node for node in doc.getElementsByTagName("yum")] for node in yumNodes: yumlist.append(t.data for t in node.childNodes if t.nodeType == t.TEXT_NODE) for ob in yumlist: for o in ob: if word not in freqDict: freqDict[word] = 1 else: freqDict[word] += 1

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• Basic questions about SNMP

  - by David Hodgson

  Hi, I'm learning about SNMP, and writing some applications using it. I have some basic questions about the protocol: Do the agents store its state on the device itself? If there is a trap set on an agent, can you do a poll on the same OID to get the same information? Without using a mib file, is there a way to query a device for all of its information at once? If not, and you're writing your own customized manager, do you have to know the structure of what it reports up front? If you're setting up an agent to report, is there usually a way to control the frequency of how often it sends a trap? Or does it usually send a trap as often as some condition is satisfied?

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• UIAlertView crashing on undocumented method

  - by morticae

  Our app has been crashing with a frequency of roughly 1 in 1,500 launches due to a bug that is proving elusive. The relevant portion of the stack trace is included. It's being fired as a callback so I have no reference for where it's occurring in my own code. It looks like what's going on is there is a UIViewAnimationState object that is calling UIAlertView's private method (_popoutAnimationDidStop:finished:). Only problem is, it appears the UIAlertView has been dealloced by this point. I don't do anything weird with alert views. I throw them up, and I wait for user input. They are all shown before being released. Anyone encountered this? At this point, I'm leaning toward it being an Apple bug. Thread 0 Crashed: 0 libobjc.A.dylib 0x3138cec0 objc_msgSend + 24 1 UIKit 0x326258c4 -[UIAlertView(Private) _popoutAnimationDidStop:finished:] 2 UIKit 0x324fad70 -[UIViewAnimationState sendDelegateAnimationDidStop:finished:] 3 UIKit 0x324fac08 -[UIViewAnimationState animationDidStop:finished:] 4 QuartzCore 0x311db05c run_animation_cal lbacks

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• Python: Decent config file format

  - by miracle2k

  I'd like to use a configuration file format which supports key value pairs and nestable, repeatable structures, and which is as light on syntax as possible. I'm imagining something along the lines of: cachedir = /var/cache mail_to = [email protected] job { name = my-media frequency = 1 day source { from = /home/michael/Images source { } source { } } job { } I'd be happy with something using significant-whitespace as well. JSON requires too many explicit syntax rules (quoting, commas, etc.). YAML is actually pretty good, but would require the jobs to be defined as a YAML list, which I find slightly awkward to use.

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• Generating a scalogram of a signal

  - by Goz

  Hi there, I'm trying to build a scalogram view for my app to see whether there is relevant information we can retrieve from a wavelet transform as opposed to using a spectograms to see what can be retrieved via an FFT. So far I can take a wave form and I can perform the forward wavelet transform on it. However I am lost at the next step. How do I turn this information into power/energy information? I have a set of wave forms at different frequencies but I have, as I say, no frequency information. Can anyone tell me what the next step is for turning this transformed data into a scalogram? Any help would be much appreciated because my google skills are failing me!

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• Gaining information from nodes of tree

  - by jainp

  I am working with the tree data structure and trying to come up with a way to calculate information I can gain from the nodes of the tree. I am wondering if there are any existing techniques which can assign higher numerical importance to a node which appears less frequently at lower level (Distance from the root of the tree) than the same nodes appearance at higher level and high frequency. To give an example, I want to give more significance to node Book, at level 2 appearing once, then at level 3 appearing thrice. Will appreciate any suggestions/pointers to techniques which achieve something similar. Thanks, Prateek

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• Only some windows shell commands work via ruby?

  - by Sanarothe

  Hi. I'm trying to use a script to control my power options since XP doesn't give you an intuitive way to change CPU Frequency options. Here's my script so far: meh = `cmd.exe /C POWERCFG.EXE /QUERY Portable/Laptop` puts "" puts meh case input when 1 then system('cmd.exe /C POWERCFG.EXE /CHANGE Portable/Laptop /processor-throttle-ac NONE') when 2 then system('cmd.exe /C POWERCFG.EXE /CHANGE Portable/Laptop /processor-throttle-ac ADAPTIVE') when 3 then `cmd.exe /C POWERCFG.EXE /CHANGE Portable/Laptop /processor-throttle-ac CONSTANT` end The problem is that the changes simply don't take place. If I run the same commands directly into a cmd.exe prompt, they work. It's very strange, but nothing works after the initial powercfg query. I feel like I'm missing something incredibly obvious. How can I get the above script to run correctly?

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• Unescape _xHHHH_ XML escape sequences using Python

  - by John Machin

  I'm using Python 2.x [not negotiable] to read XML documents [created by others] that allow the content of many elements to contain characters that are not valid XML characters by escaping them using the _xHHHH_ convention e.g. ASCII BEL aka U+0007 is represented by the 7-character sequence u"_x0007_". Neither the functionality that allows representation of any old character in the document nor the manner of escaping is negotiable. I'm parsing the documents using cElementTree or lxml [semi-negotiable]. Here is my best attempt at unescapeing the parser output as efficiently as possible: import re def unescape(s, subber=re.compile(r'_x[0-9A-Fa-f]{4,4}_').sub, repl=lambda mobj: unichr(int(mobj.group(0)[2:6], 16)), ): if "_" in s: return subber(repl, s) return s The above is biassed by observing a very low frequency of "_" in typical text and a better-than-doubling of speed by avoiding the regex apparatus where possible. The question: Any better ideas out there?

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• Learn mp3 format and audio signal processing

  - by Shankhoneer Chakrovarty

  I am trying to learn the following things: How mp3 file looks like internally? I found this: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html but it seems old. Is there any recent changes to the format? I couldnt find any. How to open a mp3 file in java and look for bytes? I tried using audiostream but I am getting a lot of zeros and signed short integers which nowhere resemble the header/body format as mentioned in the above link. Am I wrong in interpreting the bytes? How to get amplitude, frequency and pitch of a mp3 file? No idea. Can you please suggest some book or tutorial? Can you please help me in getting the solution for the above questions? I am sorry if some questions appear to be naive, I am a just begun to learn mp3. Thanks

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• Complex sound handling (I.E. pitch change while looping)

  - by Matthew

  Hi everyone I've been meaning to learn Java for a while now (I usually keep myself in languages like C and Lua) but buying an android phone seems like an excellent time to start. now after going through the lovely set of tutorials and a while spent buried in source code I'm beginning to get the feel for it so what's my next step? well to dive in with a fully featured application with graphics, sound, sensor use, touch response and a full menu. hmm now there's a slight conundrum since i can continue to use cryptic references to my project or risk telling you what the application is but at the same time its going to make me look like a raving sci-fi nerd so bare with me for the brief... A semi-working sonic screwdriver (oh yes!) my grand idea was to make an animated screwdriver where sliding the controls up and down modulate the frequency and that frequency dictates the sensor data it returns. now I have a semi-working sound system but its pretty poor for what its designed to represent and I just wouldn't be happy producing a sub-par end product whether its my first or not. the problem : sound must begin looping when the user presses down on the control the sound must stop when the user releases the control when moving the control up or down the sound effect must change pitch accordingly if the user doesn't remove there finger before backing out of the application it must plate the casing of there device with gold (Easter egg ;P) now I'm aware of how monolithic the first 3 look and that's why I would really appreciate any help I can get. sorry for how bad this code looks but my general plan is to create the functional components then refine the code later, no good painting the walls if the roofs not finished. here's my user input, he set slide stuff is used in the graphics for the control @Override public boolean onTouchEvent(MotionEvent event) { //motion event for the screwdriver view if(event.getAction() == MotionEvent.ACTION_DOWN) { //make sure the users at least trying to touch the slider if (event.getY() > SonicSlideYTop && event.getY() < SonicSlideYBottom) { //power setup, im using 1.5 to help out the rate on soundpool since it likes 0.5 to 1.5 SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); //just goes into a method which sets a private variable in my sound pool class thing mSonicAudio.setPower(1, SonicPower); //this handles the slides graphics setSlideY ( (int) event.getY() ); @Override public boolean onTouchEvent(MotionEvent event) { //motion event for the screwdriver view if(event.getAction() == MotionEvent.ACTION_DOWN) { //make sure the users at least trying to touch the slider if (event.getY() > SonicSlideYTop && event.getY() < SonicSlideYBottom) { //power setup, im using 1.5 to help out the rate on soundpool since it likes 0.5 to 1.5 SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); //just goes into a method which sets a private variable in my sound pool class thing mSonicAudio.setPower(1, SonicPower); //this handles the slides graphics setSlideY ( (int) event.getY() ); //this is from my latest attempt at loop pitch change, look for this in my soundPool class mSonicAudio.startLoopedSound(); } } if(event.getAction() == MotionEvent.ACTION_MOVE) { if (event.getY() > SonicSlideYTop && event.getY() < SonicSlideYBottom) { SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); mSonicAudio.setPower(1, SonicPower); setSlideY ( (int) event.getY() ); } } if(event.getAction() == MotionEvent.ACTION_UP) { mSonicAudio.stopLoopedSound(); SonicPower = 1.5f - ((event.getY() - SonicSlideYTop) / SonicSlideLength); mSonicAudio.setPower(1, SonicPower); } return true; } and here's where those methods end up in my sound pool class its horribly messy but that's because I've been trying a ton of variants to get this to work, you will also notice that I begin to hard code the index, again I was trying to get the methods to work before making them work well. package com.mattster.sonicscrewdriver; import java.util.HashMap; import android.content.Context; import android.media.AudioManager; import android.media.SoundPool; public class SoundManager { private float mPowerLvl = 1f; private SoundPool mSoundPool; private HashMap mSoundPoolMap; private AudioManager mAudioManager; private Context mContext; private int streamVolume; private int LoopState; private long mLastTime; public SoundManager() { } public void initSounds(Context theContext) { mContext = theContext; mSoundPool = new SoundPool(2, AudioManager.STREAM_MUSIC, 0); mSoundPoolMap = new HashMap<Integer, Integer>(); mAudioManager = (AudioManager)mContext.getSystemService(Context.AUDIO_SERVICE); streamVolume = mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC); } public void addSound(int index,int SoundID) { mSoundPoolMap.put(1, mSoundPool.load(mContext, SoundID, 1)); } public void playUpdate(int index) { if( LoopState == 1) { long now = System.currentTimeMillis(); if (now > mLastTime) { mSoundPool.play(mSoundPoolMap.get(1), streamVolume, streamVolume, 1, 0, mPowerLvl); mLastTime = System.currentTimeMillis() + 250; } } } public void stopLoopedSound() { LoopState = 0; mSoundPool.setVolume(mSoundPoolMap.get(1), 0, 0); mSoundPool.stop(mSoundPoolMap.get(1)); } public void startLoopedSound() { LoopState = 1; } public void setPower(int index, float mPower) { mPowerLvl = mPower; mSoundPool.setRate(mSoundPoolMap.get(1), mPowerLvl); } } ah ha! I almost forgot, that looks pretty ineffective but I omitted my thread which actuality updates it, nothing fancy it just calls : mSonicAudio.playUpdate(1); thanks in advance, Matthew

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• what is the idea behind scaling an image using lanczos?

  - by banister

  Hi, I'm interested in image scaling algorithms and have implemented the bilinear and bicubic methods. However, I have heard of the lanczos and other more sophisticated methods for even higher quality image scaling and I am very curious how they work. Could someone here explain the basic idea behind scaling an image using lanczos (both upscaling and downscaling) and why it results in higher quality? I do have a background in fourier analysis and have done some signal processing stuff in the past, but not with relation to image processing, so don't be afraid to use terms like "frequency response" and such in your answer :) EDIT: I guess what i really want to know is the concept and theory behind using a convolution filter for interpolation. (Note: i have already read the wikipedia article on lanczos resampling but it didn't have nearly enough detail for me) thanks alot!

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• How to estimate the thread context switching overhead?

  - by Ignas Limanauskas

  I am trying to improve the performance of the threaded application with real-time deadlines. It is running on Windows Mobile and written in C / C++. I have a suspicion that high frequency of thread switching might be causing tangible overhead, but can neither prove it or disprove it. As everybody knows, lack of proof is not a proof of opposite :). Thus my question is twofold: If exists at all, where can I find any actual measurements of the cost of switching thread context? Without spending time writing a test application, what are the ways to estimate the thread switching overhead in the existing application? Does anyone know a way to find out the number of context switches (on / off) for a given thread?

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• Properly trimming PCM data from a ByteArray

  - by Lowgain

  I have a situation where I need to trim a small amount of audio from the beginning of a recorded clip (generally somewhere between 110-150ms, it is an inconsistent amount). I'm recording in 44100 frequency and 16 bitrate. This is the code I'm using: public function get trimmedData():ByteArray { var ba:ByteArray = new ByteArray(); var bitPosition:uint = 44100 * 16 * (recordGap / 1000); bitPosition -= int(bitPosition % 16); //should keep snapped to nearest sample, I hope ba.writeBytes(_rawData, (bitPosition / 8)); return ba; } This seems to work time-wise, but all the recorded audio gets staticy and gross. Is something off about my rounding? This is the first time I've needed to alter raw PCM data so I'm not sure about the finer details of it. Thanks!

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• What's the best way to measure and track performance over various calls at runtime?

  - by bitcruncher

  Hello. I'm trying to optimize the performance of my code, but I'm not familiar with xcode's debuggers or debuggers in general. Is it possible to track the execution time and frequency of calls being made at runtime? Imagine a chain of events with some recursive calls over a fraction of a second. What's the best way to track where the CPU spends most of its time? Many thanks. Edit: Maybe this is better asked by saying, how do I use the xcode debug tools to do a stack trace?

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• Oracle - timed sampling from v$session_longops

  - by FrustratedWithFormsDesigner

  I am trying to track performance on some procedures that run too slow (and seem to keep getting slower). I am using v$session_longops to track how much work has been done, and I have a query (sofar/((v$session_longops.LAST_UPDATE_TIME-v$session_longops.start_time)*24*60*60)) that tells me the rate at which work is being done. What I'd like to be able to do is capture the rate at which work is being done and how it changes over time. Right now, I just re-execute the query manually, and then copy/paste to Excel. Not very optimal, especially when the phone rings or something else happens to interrupt my sampling frequency. Is there a way to have script in SQL*Plus run a query evern n seconds, spool the results to a file, and then continue doing this until the job ends? (Oracle 10g)

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• Error after updating to the latest version Azure SDK

  - by Mikael Johansson

  After I updated to the newest version the Azure SDK I have started to get this error several times each day when I press build in Visual Studio. The only way for me to fix it at the moment is to restart my visual studio. The error I get is: Windows Azure Tools: Invalid access to memory location Is there someone else that have got this error? And also what did you do to fix it? Thanks in advance! Update 2012-08-28: The same error still exist in VS2012 and Azure 1.7 SDK. However the frequency have gone down with VS2012.

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• how to use random bits to simulate a fair 26-sided die?

  - by Michael Levin

  How do I use a random number generator that gives bits (0 or 1) to simulate a fair 26-sided die? I want to use a bitstream to pick letters of the English alphabet such that the odds of any one letter coming up is the same as the odds of any other letter (I know real words aren't like that and have specific frequency distributions for each letter but it doesn't matter here). What's the best way to use binary 0/1 decisions to pick letters fairly from the set A-Z? I can think of a few ways to map bits onto letters but it's not obvious to me that they won't be biased. Is there a known good way?

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