Re: [RESEND] [PATCH] net: CAN: at91_can.c: decrease likelyhood of RX overruns

[Alexander Stein <alexander.stein@systec-electronic.com>]

On Monday 06 October 2014 13:39:42, David Jander wrote:
> > > One interesting control-metric would be to monitor the amount of
> > > messages/second your test-devices are able to generate.
> > 
> > I just noticed that this testing hardware has a DDR2 with only 16bit
> > interface. I think this will also reduce performance considerably. The
> 
> 16-bit DDR2 (even at its lowest clock of 200MHz) is not exactly slow... why do
> you think that could be a bottleneck?

It's a 133MHz clock, so 266MHz effective.
I had done similar tests with i.MX28-EVK which also has only a 16-bit DDR interface. The rusults were horrible. Even without that ethernet bug...
Now, doing the same tests (also CPU and Memory) again, it is worse than a AT91SAM9G20 with 32-bit SDR RAM, which also has 400 MHz. I expected both would be equally.
If you're correct and the RAM is not the bottleneck it seems that the cache (16kByte each, 32kByte on AT91SAM9G20) would be it.

> > embedded device send ~1000 CAN frames/s, each which is an average busload of
> > 20%, but in burst time, it should be 100%.
> 
> You mean the bursts of 250 messages you talked about earlier should produce a
> bus load of 100%? I think it is important to get some certainty about what's
> really going on on the bus, specially if we see things we cannot explain. You
> don't have access to a PC with a CAN interface or an oscilloscope, do you?

My PC has our USB-CAN-Modules attached (single or dual channel), so what do you want to see? a candump log?
My access to oscilloscopes rather limited and not reliable.

Best regards,
Alexander

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Dipl.-Inf. Alexander Stein

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