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by experix
Mon Dec 07, 2015 5:17 pm
Forum: Windows 10 for IoT
Topic: No interrupt?
Replies: 6
Views: 1069

Re: No interrupt?

You seem to be misunderstanding something. No modern OS is going to work on a CPU doesn't have interrupts. How would it do context switching? How would it know when to read the keyboard and mouse? How would it know when there is service needed on the network, USB and other stuff?
by experix
Sat Dec 05, 2015 5:24 pm
Forum: Camera board
Topic: new PI camera module
Replies: 7
Views: 1595

Re: new PI camera module

I suppose you want to do this because a camera board can deliver performance advantages relative to a USB camera. What are the important advantages, and how big will they be for the RPi?
by experix
Fri Dec 04, 2015 5:21 pm
Forum: Other projects
Topic: Raspberry pi central heating
Replies: 5
Views: 953

Re: Raspberry pi central heating

The thermostat is probably an on-off switch that gets moved by the shape change that temperature change causes in a bi-metallic strip. Probably a relatively low-level current flows through this switch, and that goes through a relay to switch the high current for the bioler. If you are only trying to...
by experix
Wed Dec 02, 2015 5:33 pm
Forum: C/C++
Topic: Random Number Generator Using Build In Hardware
Replies: 4
Views: 8293

Re: Random Number Generator Using Build In Hardware

dev/random blocks while the entropy pool is empty, but if pseudo-random numbers are good enough you can use dev/urandom, which is the same as /dev/random until the entropy is gone, then it switches to a deterministic pseudo-random algorithm. See more in man urandom.
by experix
Sat Nov 28, 2015 5:52 pm
Forum: Other programming languages
Topic: Binary not working
Replies: 11
Views: 1814

Re: Binary not working

You can write a C program that contains arbitrary bytes in the instruction stream. I don't remember what the appropriate directive is for gcc-- maybe 'emit', like what I used with another compiler? Actually it occurs to me that I probably did this sort of thing within an 'asm' block. I'll have to lo...
by experix
Wed Nov 25, 2015 4:29 pm
Forum: General discussion
Topic: Benchmarking a raspberrypi compared to my own PC [obsolete and locked]
Replies: 51
Views: 18135

Re: Benchmarking a raspberrypi compared to my own PC

I did a bunch of comparisons using various PCs, a Pi B+ and a Pi 2, all running http://experix.sourceforge.net (a scripting language for device control and data acquisition and analysis) and doing these tests: generating ramp and sine functions (also compared vs. octave on a Linux PC) generating a b...
by experix
Tue Nov 24, 2015 4:24 pm
Forum: C/C++
Topic: Low Level Register Access for Clock Signal: No square wave
Replies: 4
Views: 969

Re: Low Level Register Access for Clock Signal: No square wa

Viewing a 10 MHz square wave, you have to be careful about cable impedance and impedance matching at the oscilloscope input in order to avoid echoes. Have you checked that you can see a good-looking square wave from something that you know is producing one?
by experix
Tue Nov 17, 2015 5:24 pm
Forum: General discussion
Topic: Toilet detector ...
Replies: 12
Views: 1947

Re: Toilet detector ...

On Sierra Club trailbuilding outings (camping for a week in a remote place) we put a roll of TP on a stick at the trail to the latrine, and a person wanting to use the latrine would see that the TP is there, and go and take it, then put it back when done. In your situation maybe you only need a swit...
by experix
Wed Nov 11, 2015 9:04 pm
Forum: General discussion
Topic: Raspi2 and NIR Spectrometer
Replies: 2
Views: 862

Re: Raspi2 and NIR Spectrometer

I have encountered this kind of obstacle many times. I suppose your NIR sensor is a USB device or internet device, and in either case if you have the communication protocol or can convince the manufacturer to divulge it, you can make your own software. Or if you can get the source code, maybe you ca...
by experix
Mon Nov 09, 2015 4:59 pm
Forum: General discussion
Topic: opencv problem
Replies: 4
Views: 1544

Re: opencv problem

Assuming that file exists on your system, you could tell the compiler where to look for #included stuff by using a '-I' directive, or you could edit the source files to show the complete path to it, or maybe you just need to 'cd' to the directory that contains the opencv2 directory. Maybe there is a...
by experix
Sat Nov 07, 2015 7:17 pm
Forum: C/C++
Topic: memset problem
Replies: 8
Views: 1479

Re: memset problem

If a memory region can be written by an interrupt handler or even directly by hardware, you declare it volatile so the compiler takes appropriate precautions. If you then do your own writing to it, such as by memset, you take the chance that the interrupt might happen while you are doing that, and r...
by experix
Sat Nov 07, 2015 6:06 pm
Forum: C/C++
Topic: pthread questions
Replies: 30
Views: 6262

Re: pthread questions

The OP doesn't seem to have a solid grounding in thread usage, and his question comes across as a request for 1-on-1 tutoring, which probably isn't going to happen. The man pages are more helpful to people who already have some familiarity with the topic and need to review it and be reminded of deta...
by experix
Fri Nov 06, 2015 5:30 pm
Forum: General discussion
Topic: Too weird, No apps for install.
Replies: 4
Views: 818

Re: Too weird, No apps for install.

As for sourceforge, there is nothing of value there. I beg to differ. It is true that there is a huge volume of stuff on SourceForge and finding something relevant to your needs can be a daunting challenge. However, I have downloaded and installed several packages that proved very useful to me. And...
by experix
Wed Nov 04, 2015 8:07 pm
Forum: C/C++
Topic: pthread_detach causing SIGBUS: Bus error
Replies: 2
Views: 670

Re: pthread_detach causing SIGBUS: Bus error

According to man pthread_create, it can fail with EAGAIN if there are insufficient resources to create the thread. (It can also fail with EINVAL or EPERM, but the fact that it is working most of the time seems to rule out the causes of those errors.) You seem sure that there are not too many threads...
by experix
Tue Nov 03, 2015 8:03 pm
Forum: Other projects
Topic: Setting up the pulse sensor for the Pi
Replies: 1
Views: 653

Re: Setting up the pulse sensor for the Pi

This is unclear. What do you want to do? What is a pulse sensor? If you want to connect it to an ADC, I suppose its output signal must be a voltage that varies with time, and you want to examine such things as the maximum, the duration, the envelope shape and so on. Then you need to start with the e...
by experix
Thu Oct 01, 2015 4:27 pm
Forum: General discussion
Topic: kernel error
Replies: 2
Views: 530

Re: kernel error

I gather that this is a module which you wrote. It seems to have tried to make an illegal memory reference in a function called uart_begin. If you can't find an error by inspecting the C program, you need to look at the disassembled code surrounding the address where it crashed, and in particular th...
by experix
Mon Sep 28, 2015 4:19 pm
Forum: Automation, sensing and robotics
Topic: reading serial data from sensor
Replies: 11
Views: 2596

Re: reading serial data from sensor

I needed to operate a Gertbot (which uses serial communication for everything) at high speed. Sending or receiving in bulk is not an option because you have to send a little command and then get a little answer, and so on. But the operating system interface is a big (or should I say little?) bottlen...
by experix
Mon Sep 28, 2015 4:09 pm
Forum: C/C++
Topic: Problem linking to trigonometric library.
Replies: 4
Views: 1953

Re: Problem linking to trigonometric library.

If you look up 'man acos' it gives you this info at the top:

Code: Select all

#include <math.h>
and
Link with -lm
What I don't know is why your linking went ok before. Something somewhere must have told the linker to link the math library. I would like to know where defaults like that come from.
by experix
Sat Sep 26, 2015 5:04 pm
Forum: Automation, sensing and robotics
Topic: High Current Stepper Control
Replies: 3
Views: 883

Re: High Current Stepper Control

The Gertbot has 4 H-bridges rated 2.5A, and you can certainly get H-bridges alone if you want to build your own thing. And there must be other boards out there that have bridges with enough capacity for you. Your remark about putting resistors in series with the motors suggests you may have chosen m...
by experix
Fri Sep 11, 2015 8:06 pm
Forum: General discussion
Topic: Another Usability issue
Replies: 2
Views: 569

Re: Another Usability issue

If this is the biggest issue you can find, it must be a **really** good system!
by experix
Tue Sep 08, 2015 4:03 pm
Forum: General programming discussion
Topic: Serial - Send a character
Replies: 11
Views: 3674

Re: Serial - Send a character

I needed to get faster action on the serial port than what could be achieved by reading/writing /dev/ttyAMA0 (the userland-kernel transition was eating up too much time when I tried to control hardware using short messages back and forth). I wrote a userland tty driver and got about 7x speed improve...
by experix
Tue Sep 08, 2015 3:39 pm
Forum: Advanced users
Topic: How can I get the exposure time of Pi camera?
Replies: 7
Views: 1733

Re: How can I get the exposure time of Pi camera?

You have two exposure problems to contend with. The sky has big differences in brightness from horizon to where the sun is, and the fisheye lens probably has a big difference in exposure between the center and periphery. Maybe you can adjust your shutter speed to avoid saturating too much of the cen...
by experix
Tue Sep 08, 2015 3:30 pm
Forum: Advanced users
Topic: Another question about the RasPi Camera
Replies: 3
Views: 608

Re: Another question about the RasPi Camera

If the purpose is to get an image size (pixel dimensions) smaller than the camera sensor dimensions, you can reduce the original image by cropping (if you only want a part of it) or by transforming the whole thing into smaller pixel dimensions. ImageMagick can do both of those. Or you may get a big ...
by experix
Mon Sep 07, 2015 7:57 pm
Forum: General discussion
Topic: Sound Advice?-SOLVED
Replies: 3
Views: 783

Re: Sound Advice?

I think your are better off controlling the gain of the amp, not the input signal.
by experix
Mon Aug 31, 2015 4:03 pm
Forum: Camera board
Topic: Picam respond linearly as a function of light intensity?
Replies: 9
Views: 1543

Re: Picam respond linearly as a function of light intensity?

I also don't know the answer-- I only know more questions. When you speak of intensity, would that be photons per second, or power? For any particular color these are proportional, but the factor depends on the color. Or maybe you are more interested in the electric field strength. That is related t...

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