## Thursday, 19 January 2017

### Gnuplot/C On A Mac

I recently updated my Mac to Big Sur and found the previous Gnuplot (http://gnuplot.info/) installation procedure using Homebrew is no longer the best method so I've updated this blog post.

First install Gnuplot on Big Sur:
If you have MacPorts (https://www.macports.org/) installed then update it:
sudo port -v selfupdate
If you do not have MacPorts installed then you can install it by opening the following URL:
Install gnuplot using MacPorts:
sudo port install gnuplot +wxwidgets
(I like the wxwidgets API)

Perfect, lets test gnuplot :

$gnuplot gnuplot> plot sin(x) We should now see a nice little sinusoid graph. Now let's build Gnuplot/C :$ cd gnuplot_c/src/
$make -f makefile.macos Now let's test Gnuplot/C :$ cd gnuplot_c/examples/
$./br.sh LinesAndPoints We should now see the graphs plotted. Note, if you see the following message: sh: /dev/nul: Permission denied Then you need to do the following:$ sudo mknod /dev/nul c 1 3
$sudo chmod 666 /dev/nul Now let's test Gnuplot/C again:$ ./br.sh LinesAndPoints

Excellent. All running nicely :-)

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.
Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

## Sunday, 8 January 2017

### Some Thoughts On Benchmarking Applications On A Pentium PC (Windows/Mac/Linux)

The ability to benchmark DSP algorithms to check that they execute in real time is a key part of the DSP development process. I've written several blog posts on the subject including :

http://blog.numerix-dsp.com/2013/01/how-to-benchmark-some-c-code-or.html
http://blog.numerix-dsp.com/2015/01/timing-code-running-on-xmos-xcore.html

While benchmarking code to run on a traditional DSP or embedded microcontroller is a relatively simple task, due to the deterministic nature of DSP architectures, doing the same on a Pentium PC is quite tricky. I've recently tried two of the most common techniques for benchmarking DSP algorithms on a Pentium PC. The two techniques are :

Reading the Pentium Time Stamp Counter Register : http://stackoverflow.com/questions/9887839/clock-cycle-count-wth-gcc
Instruction counting using GDB : http://stackoverflow.com/questions/21628002/counting-machine-instructions-using-gdb

The Time Stamp Counter option has a lot of disadvantages when used in a multi-tasking OS due to the whole task switching happening in parallel with the application.
The inital overhead calculation may take longer, due to a task switch, so the final benchmark may take less than 0 cycles when subtracting the overhead of calling the timer functions.

The GDB solution counts instructions but does not allow for pipelining, caching, and run-time parallel instruction execution.

So far the only option I have come up with is to use a statistical analysis of the results to get an approximation to how efficient an algorithm is.

Here are some results from some different filter functions that I have benchmarked (more details in an upcoming post about the different filtering functions).

The TSC technique shows that runtime parallelization of code gives better than 1 instruction per cycle execution but each mode was executed a twenty times and the average result was taken so take note of the problems listed above.

MODE    GDB         TSC
1              2514          975
2              1171          754
3              1188          547

In summary, GDB instruction counting gives a good approximation to how efficient an algorithm is but the Time Stamp Counter solution gives a better estimate to the actual number of CPU clock cycles are required.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.
Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/

## Tuesday, 3 January 2017

### Gnuplot/C Update II

A new version of Gnuplot/C has been uploaded to SourceForge that includes polar plotting capabiliites : https://sourceforge.net/projects/gnuplotc/.

This adds logarithmic x-axis support to the existing plot types.

Here is an image showing the capabilities :

The DTMF tones were generated using the SigLib DSP library.

If you have found this solution useful then please do hit the Google (+1) button so that others may be able to find it as well.
Numerix-DSP Libraries : http://www.numerix-dsp.com/eval/