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    SubjectRe: [PATCH] lis3lv02d: add axes knowledge of HP Pavilion dv5 models
    Giuseppe Bilotta schreef:
    > On Tue, Feb 10, 2009 at 10:39 PM, Giuseppe Bilotta
    > <giuseppe.bilotta@gmail.com> wrote:
    >> On Tue, Feb 10, 2009 at 11:10 AM, Pavel Machek <pavel@suse.cz> wrote:
    >>> Yeah, that patch. Not sure what to do next... you could grab lis3
    >>> manual and see if you can setup chip by hand to get better results...
    >> As Eric pointed out, it looks definitely like an endianness problem,
    >> although there are a few strange things which are happening at the
    >> same time. Is the lis3 manual available online somewhere, or can I
    >> request it to the mfgr?
    >
    > 'k, found it on the STMicroelectronics website. Reading the doc about
    > LIS3LV02DL I see that WHO_AM_I should return 3Ah, but my sensor
    > returns 3Bh. I'll see if I find the correct datasheet for this one
    > instead, it might have info about the differences.
    Yeah, we accept also 3Bh for the who_am_i (see in hp_accel.c). The
    reporter who had a laptop with such chip never reported any problem and
    I didn't pay attention enough to notice those chips have only 8bits
    precision.

    > One thing that I noticed is that (modulo axis inversion) I'm able to
    > use the sensor correctly if I set the thing to only use the high byte,
    > totally discarding the lower byte:
    > return *((s8*)(&hi));
    > Maybe this sensor needs a different setup to return 12 instead of 8
    > bits of information.
    So you probably have a lis202dl (which has only two axes of 8bits each)
    or a LIS302DL (3 axes of 8 bits):
    http://www.st.com/stonline/products/literature/ds/13624/lis202dl.htm
    http://www.st.com/stonline/products/literature/ds/12726/lis302dl.htm

    Unfortunately, the WHO_AM_I register returns 3Bh in both cases. I'd tend
    to imagine it's a three axes chip, but you can confirm that by just
    checking if Z has any meaningful value. You can then modify
    lis3lv02d_read_16() to only return the byte as low byte and the high
    byte as FFh if the high bit of the value is set (because I guess they
    are signed integers). You also have to change MDPS_MAX_VAL to 128, to
    get things completely right.

    Once we have this sorted, we should add a flag to know if the current
    device is 8 bits or 12 bits, depending on the value of who_am_i. This
    would allow the driver to work fine with both type of chip.

    Eric


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