[pskmail] Re: Robust psk-modes on raspberry pi

  • From: John Douyere <vk2eta@xxxxxxxxx>
  • To: pskmail@xxxxxxxxxxxxx
  • Date: Tue, 5 Nov 2013 13:04:29 +1100

Hello Tarmo,

If you have correct decoding with PSK modes but not PSKR modes then the
most likely reason is processing power.

The processing load on the CPU is significantly higher due to the double
Viterbi decoder and interleavers used for the PSKR decode.

I have seen that issue on the earlier Android devices when I developed the
andPskmail program.

If you look at the rxpsk source code in the Android program (in Java) you
will see that I spend time to work around these limitations. One solution I
used quite effectively was to reduce the order of the filters to free-up
some resources.

From memory I reduce the order from 64 to 32, which means a slight out of
band increase in interference but overall better than not having decode at
all.

But if you say that TXing is also not decodable, then I suspect that the
CPU is simply not capable of processing that load.

A good test would be to try the MFSK and THOR modes as well because the
MFSK modes are very resource effective and the THOR modes the most CPU
hungry.

In my experience on the Android devices (from memory) here is the
approximate hierarchy of CPU load by mode:

PSK31
...
PSK500
MFSK16
...
MFSK64
PSK63F
PSK125R
...
PSK500R
THOR8
...
THOR22

So have a look if the top of the list works but not the bottom. That should
give you a good indication if the CPU is the issue or not.

Also, have a look in Fldigi what interpolator you use. The linear one is
the most CPU efficient.

I also assume you have already selected the "Slow CPU" option in Fldigi.

73, John



On Tue, Nov 5, 2013 at 12:03 PM, Tarmo Huttunen <tarmopaha@xxxxxxxxx> wrote:

> Hello...
>
> I have wondered this oddity with raspberry-fldigi-jpskmail for a while:
>
> Psk-r modes are not working. Sympton is, after psk-r id is received,
> raspberry does not decode anything. I mean, there will not come any
> characters on fldigi window. Is that "normal" sympton related to slow cpu?
>
> In normal pc-setups if psk-r decoding fails, there will come at least some
> nonsense text, am I right?
>
> I have started to wonder, if this psk-r problem is after all related to
> prosessing power at all? Could this have something to do with varicode used
> on psk-r modes? Missing symboltable or something similar?
>
> If I remember right, I also havent got pc to decode psk-r sent by
> raspberry. (This was not what I was testing, just something I happend to
> notice, and I am at work now, can not test again.)
>
> Do somebody have some advice for me, where should I look? Have somebody
> used robust psk-modes on some other low-resource machine?
>
> Thanks
> Tarmo, OH6ECF
>

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