On 08/22/2018 03:40 PM, Danny Smith wrote: > > > On 08/22/2018 03:05 PM, Lars-Peter Clausen wrote: >> On 08/22/2018 09:53 AM, Danny Smith wrote: >>> >>> On 08/22/2018 08:34 AM, Lars-Peter Clausen wrote: >>>> On 08/22/2018 08:11 AM, Robert Rosengren wrote: >>>>> From: Danny Smith <dannys@xxxxxxxx> >>>>> >>>>> Fixed range in safeload conditional to allow safeload to be used from >>>>> 4 bytes. >>>> Hi, >>>> >>>> Thanks for the patch. The reason why 4 bytes is excluded is that up to 4 >>>> bytes can be updated atomically with a single register write. But I could >>>> see that if the firmware reads the same parameter multiple times during the >>>> same run you could get inconsistent results. >>>> >>>> Can you explain a bit more why you need this? >>>> >>>> If we want to allow safeload for 4 byte parameters the same reasoning >>>> applies for parameters with less than 4 bytes as well and so the check >>>> should be removed completely. >>>> >>>> - Lars >>> Hi, >>> >>> Thanks for the feedback. It is correct that up to 4 bytes can be updated >>> atomically but does that also guarantee that the data is safeloaded, i.e. >>> updated when the parameter is not in use? Maybe updating up to 4 byte >>> parameters without safeload does not cause audio glitches? >> The datasheet says: >> >> """ >> To update parameters in real time while avoiding pop and click >> noises on the output, the ADAU1761 uses a software safeload >> mechanism. The software safeload mechanism enables the >> SigmaDSP core to load new parameters into RAM while guaranteeing >> that the parameters are not in use. This prevents an >> undesirable condition where an instruction could execute with >> a mix of old and new parameters. >> """ >> >> The way I understand the last sentence is that there is no issue when >> loading only 4 bytes or less since there is no risk of mixing old and new >> data. >> >> I don't mind changing this, I was just curious if you had seen any issues >> with a 4 byte parameter update. >> >> - Lars > I have not seen any issues doing a 4byte parameter update without safeload > but have not performed any extensive testing on the subject. The reason for > the patch was that I noticed that sigmastudio uses safeload when doing 4byte > writes but I cannot say if it is necessary or not. Ok, then lets change the driver, but drop the test completely so that anything up to 20 bytes uses safeload. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
