On 24.05.2016 09:45, Linus Walleij wrote:
On Mon, May 23, 2016 at 6:29 PM, Jonathan Cameron
<jic23@xxxxxxxxxxxxxxxxxxxxx> wrote:
I forgot this part also has gain and offset trim registers. Will add
them before
applying as that is easy enough and reduces the differences further.
These exist on some other parts but we can add them any time.
LIS3LV02DL also has x,y,z offset and gain trim registers, but when
I read up on it, I understood that these are just factory-programmed
registers. I.e. they are undocumented in the register list, but a table
states them as "calibration" and "loaded at boot".
So I always understood them as something the sensor loads at
boot to calibrate itself, so you can ignore the contents, and they
probably exist on the other sensors too, albeit undocumented as
they have no use.
I toyed with the idea of reading them and pusing the values to the
entropy pool with add_device_randomness() as they are device-unique
data.
But if you have proper docs on them I guess maybe they are used
differently on your sensor...
Yours,
Linus Walleij
As I understand it you can actually apply corrections to them (was
certainly
how I read that years ago). Take into account that these early sensors
were
incredibly noisy and perhaps more prone to shock damage than newer ones.
(my test sensor will vary by 10% or more whilst sat on a steady concrete
floor - even with huge levels of oversampling...)
Back then we were using some sensors where if you dropped them on the
floor
you had to send them back to the manufacturer for recalibration before
they
were remotely useful again.
Funnily enough, given we had them attached to people that happened all
the
time :(
ST certainly aren't believers in 'detailed' documentation. Always feels
like somewhat of a guessing game when implementing drivers for their
parts.
J
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