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 <hswee...@visionengravers.com>
Cc: Ian Abbott <abbo...@mev.co.uk>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
drivers/staging/comedi/drivers/usbduxfast.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/comedi/drivers/usbduxfast.c
b/drivers/staging/comedi/drivers/usbduxfast.c
index 60f1c5e..9e846b4 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);
--
2.4.3
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