Il giorno ven 13 set 2019 alle ore 13:30 Couret Charles-Antoine <charles-antoine.couret@xxxxxxxxxxxxx> ha scritto: > > Hi, > > Le 13/09/2019 à 10:30, Andrea Merello a écrit : > > Il giorno ven 13 set 2019 alle ore 09:19 Ardelean, Alexandru > > <alexandru.Ardelean@xxxxxxxxxx> ha scritto: > > > >> So, at power-up this chip seems to need 2 dummy reads to discard data. > >> Which seems to happen in ad7949_spi_init() > >> > >> One thing that maybe could be optimized (for the driver), is in `ad7949_spi_read_channel()` to use the current-channel & > >> not do a SPI write to change the channel if it doesn't change. > >> > >> Datasheets (in general) are not always obvious about describing chip behavior for SW (or for writing a driver), but I > >> would suspect that if you are reading garbage data, it could be that the channel has changed. > >> This is true for some other ADCs. > >> And requires testing for this one. > > Yes, it's exactly what I've seen here. If the channel does not change > > then the AD is already in acquisition phase on the right channel (I > > assume it's OK to keep it in such phase indefinitely), then we can > > just trigger a new conversion (CNV low->high, that is a dummy xfer) > > and then read the result in following xfer, as the driver already did. > > > > I craft a V2 that performs the extra (3rd) spi xfer only if the > > channel has to change. > > This design should be ok. I didn't implement in that way because not > enough time to optimize the driver before release (I don't have access > to the chip anymore) and for our workflow it was not relevant (we > scanned all channels). > > > About your fix to read / write several times before reading the value > after channel change seems not relevant. Did you try with the current > implementation? Because when I developed the driver, I have always got > the expected value for each channel with this design. Yes, I did. But I experienced the said problems. I don't have idea about why it worked for you and it didn't for me.. By scanning the channels in circular fashion, with the current implementation, I would expect to get values off-by-one (i.e. you read ch ...,0,1,2,3,4,0,1,2,3,4,... and you get value for ch ...,4,0,1,2,3,4,0,1,2,3,...). > > Just to be sure we are not adding useless steps. > > >> Added Charles-Antoine, since he wrote the driver. > >> Shoud have added him on the other patches as well, but I just remembered. > > I tried on my first answer, but apparently mails to his address bounce > > back with a failure response.. > > But now it seems ok. Did you put the right email address? Sorry, my fault. I've done a mistake in copy-and-paste. > > Thank you for the copy. > > Regards, > > Charles-Antoine Couret >
