Tuomas <tvainikk _at_ gmail _dot_ com> reported problems getting meaningful output from a Lab-PC+ in differential mode for AI cmds, but AI insn reads gave correct readings. He tracked it down to two problems, one of which is addressed by this patch. It seems the setting of the channel bits for particular scanning modes was incorrect for differential mode. (Only half the number of channels are available in differential mode; comedi refers to them as channels 0, 1, 2 and 3, but the hardware documentation refers to them as channels 0, 2, 4 and 6.) In differential mode, the setting of the channel enable bits in the command1 register should depend on whether the scan enable bit is set. Effectively, we need to double the comedi channel number when the scan enable bit is not set in differential mode. The scan enable bit gets set when the AI scan mode is `MODE_MULT_CHAN_UP` or `MODE_MULT_CHAN_DOWN`, and gets cleared when the AI scan mode is `MODE_SINGLE_CHAN` or `MODE_SINGLE_CHAN_INTERVAL`. The existing test for whether the comedi channel number needs to be doubled in differential mode is incorrect in `labpc_ai_cmd()`. This patch corrects the test. Thanks to Tuomas for suggesting the fix. Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 3.7.x, 3.8.x --- Note: needs backporting for earlier kernels. --- drivers/staging/comedi/drivers/ni_labpc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/staging/comedi/drivers/ni_labpc.c b/drivers/staging/comedi/drivers/ni_labpc.c index 10bd2b3..f851c54 100644 --- a/drivers/staging/comedi/drivers/ni_labpc.c +++ b/drivers/staging/comedi/drivers/ni_labpc.c @@ -1204,7 +1204,8 @@ static int labpc_ai_cmd(struct comedi_device *dev, struct comedi_subdevice *s) else channel = CR_CHAN(cmd->chanlist[0]); /* munge channel bits for differential / scan disabled mode */ - if (mode != MODE_SINGLE_CHAN && aref == AREF_DIFF) + if ((mode == MODE_SINGLE_CHAN || mode == MODE_SINGLE_CHAN_INTERVAL) && + aref == AREF_DIFF) channel *= 2; devpriv->command1_bits |= ADC_CHAN_BITS(channel); devpriv->command1_bits |= thisboard->ai_range_code[range]; -- 1.8.1.1 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/devel
