On 09/03/10 21:03, Andrew Chew wrote: >> if I understand your comment correctly userspace needs to know that >> number to convert from the magn_raw values to standard units. >> Hence it must be exported. My point is that the calib attributes >> are used for devices that do their calibration offsets and scales >> internally. If it is a value userspace needs to apply then the >> correct parameters are scale and offset. In the majority of devices >> see so far these are fixed for all instances of the same part. That >> isn't true here. >>> >>> And if we were to emit non-raw values (or provide the scale >>> attributes), what's theexact name of the attributes? And >> what units are we expecting? Gauss? Tesla? I don't see >> that documented anywhere. >> That is documented. Gauss is the chosen standard for >> magnetometers. I'll assume the >> conversion factors are channel dependent in which case you need >> >> magn_x_raw, magn_x_scale, magn_x_offset >> >> note again, we have documented everything for some device types. >> At the time, repeating for all of them was considered redundant, but >> perhaps we do need to do this for the added clarity. >> >> The value in Gauss = (magn_x_raw + magn_x_offset)*magn_x_scale > > The conversion formula doesn't have an offset, actually, so the order > in which the offset and scale are applied don't really matter to me. Cool. I misread your comment (lots of brackets and I was clearly half asleep ;) > > In any case, I think I got it now. I'm going to report the raw sensor > value, and the scale factor for each axis to convert to gauss. > > I assume when you say magn_x_scale, you really mean magn_x_gain? > Because I don't see magn_x_scale defined in magnet.h. Or should I > call the attribute magn_x_scale anyway, and not use the IIO_DEV_ATTR > macro for gain? Gah. Take the documentation first. Looks like the magnetometer macros slipped through the net - mainly because no one was using them so they shouldn't have been there in the first place. Please can you add suitable macros for _scale? You can also kill the _gain ones if you like, or I can add that to the next set of clean up patches. Killing the gain ones should be in a separate patch but it'll obviously cause merge issues hence it is easier for you to do both. The only provider of such an attribute is imu/adis16400_core.c and that one is constant and shared across the axes so it uses IIO_CONST_ATTR(magn_scale,...) Thanks for pointing this out. Jonathan ----------------------------------------------------------------------------------- > This email message is for the sole use of the intended recipient(s) and may contain > confidential information. Any unauthorized review, use, disclosure or distribution > is prohibited. If you are not the intended recipient, please contact the sender by > reply email and destroy all copies of the original message. > ----------------------------------------------------------------------------------- > -- 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
