Improving PS2 decoding

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Marconi
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Joined: Mon Jun 14, 2021 4:16 pm

Improving PS2 decoding

Post by Marconi »

Is there a way to improve PS2 keyboard decoding please?

The attached segment is from a working keyboard and PC. This is just one example, sometimes a second capture will give the correct information.

The PC sends $F5, the keyboard returns $FA, the next packet from the PC is not decoded but is clearly $FF. The information shows as an invalid packet length and parity invalid.
Attachments
Keyboard.JPG

bennog
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Location: Netherlands

Re: Improving PS2 decoding

Post by bennog »

It looks like your sample rate is too slow.
Try increasing the value of the 1 MS as shown below to 10 or 100 MS.

Also turn decoding off during the capture, in some situations this will allow for higher sample counts.
2021-06-24_08-15-34.png
This one is with the settings you did and resulted in a sample rate of 100kS/sec on my 3403
2021-06-24_08-22-53.png
This one is with 10MS max samples per trace and resulted in 1MS/sec
2021-06-24_08-23-31.png
Benno

Marconi
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Joined: Mon Jun 14, 2021 4:16 pm

Re: Improving PS2 decoding

Post by Marconi »

Thanks for the suggestion. I tried increasing the sample rate and turning off decoding during capture on my 2405A but that did not help.

bennog
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Posts: 86
Joined: Mon Nov 26, 2012 9:16 am
Location: Netherlands

Re: Improving PS2 decoding

Post by bennog »

Look at the property's screen and see how you get the sample rate, as highlighted in my screenshots above 100kS/s.

I know the 2405A is a limited device because it has only 48k sample memory, so there streaming data rate is limited.
Options you can try.
- Decrease timebase from 1s/div to 0.5 or 0.2 s/div.
- Test with picoscope V7 if you can get higher sample rate as 100kS/s

Benno

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