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. Regards, Hartley _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
