diff options
| author | H Hartley Sweeten <hsweeten@visionengravers.com> | 2015-08-24 10:14:03 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-09-12 18:24:25 -0700 |
| commit | a05e94bd5230a90eca2905495e764a0ad707c498 (patch) | |
| tree | 398b5d9a474c1af1882f5115504284f45a28ddd5 /drivers/staging/comedi/drivers/usbduxfast.c | |
| parent | 7b0fc5baa0bd75fa04cd784828d7d072fb905144 (diff) | |
staging: comedi: usbduxfast: document strange ai maxdata
The subdevice 'maxdata' is typically a mask of the valid bits that can
be returned by a subdevice, (1 << bits) - 1. The analog inputs of this
device have a resolution of 12-bits so the 'maxdata' should be 0x0fff.
But, this hardware can produce a value of 0x1000 indicating an overflow
from the ADC. The comedilib library's comedi_to_phys() function will
then return NAN when this value is read from the hardware.
Add a comment to clarify the strage 'maxdata' value.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/staging/comedi/drivers/usbduxfast.c')
| -rw-r--r-- | drivers/staging/comedi/drivers/usbduxfast.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/staging/comedi/drivers/usbduxfast.c b/drivers/staging/comedi/drivers/usbduxfast.c index 60f1c5e15a6a..9e846b43f54e 100644 --- a/drivers/staging/comedi/drivers/usbduxfast.c +++ b/drivers/staging/comedi/drivers/usbduxfast.c @@ -865,7 +865,7 @@ static int usbduxfast_attach_common(struct comedi_device *dev) s->do_cmdtest = usbduxfast_ai_cmdtest; s->do_cmd = usbduxfast_ai_cmd; s->cancel = usbduxfast_ai_cancel; - s->maxdata = 0x1000; + s->maxdata = 0x1000; /* 12-bit + 1 overflow bit */ s->range_table = &range_usbduxfast_ai_range; up(&devpriv->sem); |