On 23/11/15 16:15, Marc Titinger wrote: > On 21/11/2015 19:13, Jonathan Cameron wrote: >> On 18/11/15 14:38, Marc Titinger wrote: >>> Basic support or direct IO raw read, with averaging attribute. >>> Values are RAW, INT_PLUS_MICRO (Volt/Ampere/Watt). >>> >>> Output of iio_info: >>> >>> iio:device0: ina226 >>> 4 channels found: >>> power3: (input) >>> 1 channel-specific attributes found: >>> attr 0: raw value: 1.150000 >>> voltage0: (input) >>> 1 channel-specific attributes found: >>> attr 0: raw value: 0.000003 >>> voltage1: (input) >>> 1 channel-specific attributes found: >>> attr 0: raw value: 4.277500 >>> current2: (input) >>> 1 channel-specific attributes found: >>> attr 0: raw value: 0.268000 >>> 4 device-specific attributes found: >>> attr 0: sampling_frequency_available value: 61 120 236... >>> attr 1: in_averaging_steps value: 4 >>> attr 2: in_calibscale value: 10000 >>> attr 3: in_sampling_frequency value: 1506 >>> >>> Tested with ina226, on BeagleBoneBlack. >>> >>> Datasheet: http://www.ti.com/lit/gpn/ina226 >>> >>> Signed-off-by: Marc Titinger <mtitinger@xxxxxxxxxxxx> >> You have added some new ABI in here, but I'm not seeing any documentation >> for averaging_steps. Does this map onto the existing oversampling_ratio? >> > > I am not sure normal averaging maps well with oversampling. Normal > averaging will provide one value every N samples (this is what this > chip does), while oversampling will interpolate N value between > sample 'k' and 'k-1', and decimate to provide a less-noisy version of > sample 'k', the resulting sampling frequency is not lower. > Oversampling is wonderfully badly defined as a term. Often it is use precisely for the method or noise reduction that is infact just an average. Usually it implies: 1) Sampling at a higher rate than the eventual output will be provided at. This is the oversampling bit. 2) Sometimes adding carefully controlled noise - effectively dithering but ensuring the noise is not at a frequency of interest so it can be removed later without effecting what we are after - this allows obtaining a theoretically higher bit rate signal than what you are measuring with - in extreme cases it allows the one bit adc trick - more commonly it's just about reducing the noise as a result of the measurement process. 3) ADC conversion - post noise addition if we are deliberately adding some. 4) Applying digital filters as desired. 5) Finally outputing at the reduced data rate. So - in the simplest form we actually have a straight forward average filter just like the one your device is applying. Now you are correct that the data goes digital at a much higher rate than the output rate in oversampling - however if we assume a chip is providing an oversampling function inherently it must then be dropping it down to a more reasonable level in chip (rather than leaving it to the CPU) Hence if we have an iio chip with oversampling it's applying a filter - whether that is a simple average filter, or something a touch more clever is the only real question. Now I've probably confused this discussion even more ;) Jonathan -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
