--- In "Anouk Ahamitet" <> wrote:
>
> We're having trouble getting accurate results from a PC-104 A2D board
> that we want to use for a project that will likely be using the TS-7800
> SBC. We have two other intel-based SBCs that also run linux and the A2D
> provides very accurate results (standard deviation of 0.06 after a few
> minutes to warm up) when connected to both of those boards. When
> connected to the 7800, the readings from the board are far less stable,
> with a stddev of over 2.5 after the same amount of time or reads (the
> code on the 7800 seems to run about 1/2 the speed of the other boards --
> we're not sure exactly why).
>
> Aside from adjusting the port I/O between the intel and ARM, we're
> running the exact same program on all three systems.
>
> Has anyone else experienced anything like this? Does anyone know what
> the cause might be? Is there any way to correct it (other than
> redesigning our enclosure to fit one of the other SBCs and returning all
> of the 7800 we bought)?
>
Well, you've not given enough details to make any intelligent comments.
* What's your input signal like during testing? I guess if you are calculating
standard deviation, you are holding (or trying) to hold the input constant.
What readings do you get, and what do you expect?
* What sampling frequency?
* How is data taken / transferred from your A/D card? Userland or kernel
driver?
* What kernel versions for x86 & ARM? glibc versions?
* What do you observe about the ARM data? Random noise, HF noise?
* Have you ruled out a bad A/D card on the 7800 system?
My first guesses would be RF interference with your analog stage, or timing
jitter (your data is not sampled when you think it is), or even endian-ness
issues.
You don't really say what 'code' is running running slower. If you do any
floating point at all, that can have slight to severe impacts on your program
speed on ARM, depending on your system. If you are only talking of the
acquisition time, you really can't discuss it without posting the code you are
using.
regards, ......... Charlie
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