On 2014-06-23 18:45, Hartley Sweeten wrote:
On Monday, June 23, 2014 8:10 AM, Ian Abbott wrote:
On 2014-06-20 21:13, H Hartley Sweeten wrote:
The DT2821 series board have jumpers that set the output range for
the two Analog Output channels. The range_table for the Analog Output
subdevice provides all possible ranges to the user. When a unipolar
range is selected the board expects the data to be in a straight
binary format. When a bipolar range is select the data should be in
two's complement format.
Currently, the user passes some configuration options when attaching
to the driver to select the data format for each channel. If the
user does not pass the config options, the data format is assumed to
be straight binary.
The Analog Output subdevice now has a range_table that provides the
user will all possible ranges. Use the range information to determine
if the data values need to be munged into two's complememnt values
and deprecate the config options.
I don't think there's any physical requirement for the 2's
complement/straight binary jumpers to match the range jumpers. The 2's
complement/straight binary jumper will just invert or pass through the
top bit of the data value.
A downside of this patch is that users may have to open up their
computer to set the jumper how comedi expects it to be, rather than just
telling comedi how the jumper is set on the board via the attach option
(although the options were handled incorrectly anyway and fixed by your
patch 06). Particularly in this case, the default option values for
options 6, 7, 9 and 10 would have been to assume the +/-10V range with
straight binary coding, but this patch changes it to assume 2's
complement encoding for the +/-10V range.
In general, I feel it's best not to mess with the attach option values
unless they're obviously buggy.
These legacy boards can be a pain with all the jumper options...
For manual for the DT2821 series states this for the D/A subsystem:
"Tables 3-10 and 3-11 indicate jumper selections
for the output range for each DAC and the factory
configuration. When jumpered for unipolar
operation, the DT2821 series board expects digital
data in straight binary coding. When set for
bipolar mode, the DT2821 series board expects
digital data in offset binary coding only."
Based on that it appears there is a physical requirement.
In that case I agree there's no point having options to configure the
encoding of the AO channels' data.
--
-=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@xxxxxxxxx> )=-
-=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
_______________________________________________
devel mailing list
devel@xxxxxxxxxxxxxxxxxxxxxx
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
