Andrew, Thank you for your inputs.
> Can you elaborate on your "EDMA runs at a lower speed" comment ? The > usual setup is to have McASP trigger EDMA transfer. An EDMA transfer > runs at CPU speed. It should be plenty fast enough at 96 MHz. > EDMA here runs at 48MHz and McASP triggers the EDMA transfer. > In the past I have seen issues where the CPU cache updating has priority > over the McASP transfer in the EDMA sub-system. That can cause McASP > underruns. I would first check that the EDMA is configured so that the > McASP transfer has priority over everything else. I'm not an expert on > EDMA3, but I think that was one of the improvements they made over > regular EDMA. > McASP events have the highest priority in EDMA in case events arrive simultaneously from various channels. The audio clock is from the codec and will not be affected by frequency scaling. Also when playback or record is running, CPU load is about 4%, so this is not a bottleneck either. The only thing that is affected by frequency scaling is EDMA. Based on these practical observations, it seems that EDMA is not able to transfer data fast enough. Let me see if I can check this theoretically too. Regards, Chaithrika > Cheers, > Andrew > > Chaithrika U S wrote: > > Kevin, > > > > With the cpufreq support on DA850/OMAP-L138 SoC we are observing > > that audio does not function as expected at all sampling rates > > for various operating points. At a CPU frequency of 96MHz, audio > > works fine with a sampling frequency of 8kHz. For other sampling > > rates, there are lot of underrun/overrun errors. This is because > > of EDMA also runs at a lower speed and is not able to transfer > > data at the desired rate. > > > > To overcome the above, we can depend on the user to set the scaling > > min frequency to be the same as scaling max frequency (in this case > > 300 MHz) before starting aplay/arecord or temporarily move to > > performance governor so that the audio quality is not affected. > > > > Do you think this is the right approach to this problem? Any other > > solutions you suggest exploring? > > > > Regards, > > Chaithrika > > > > > > > > _______________________________________________ > > Davinci-linux-open-source mailing list > > Davinci-linux-open-source@linux.davincidsp.com > > http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source > > > > > > _______________________________________________ Davinci-linux-open-source mailing list Davinci-linux-open-source@linux.davincidsp.com http://linux.davincidsp.com/mailman/listinfo/davinci-linux-open-source
