[PATCH 2/4] staging: comedi: ii_pci20kc: only bipolar ao ranges are 2's complement

[Ian Abbott]

On 07/10/15 19:09, H Hartley Sweeten wrote:
> According the the PCI-2006M user's manual, bipolar ranges use 2's
> complement coding and unipolar ranges are straight binary. Fix
> ii20k_ao_insn_write() to use the correct coding based on the range.
>
> For aesthetics, use the comedi_offset_munge() helper to handle the
> munging of the data.
>
> Signed-off-by: H Hartley Sweeten <hsweeten at visionengravers.com>
> Cc: Ian Abbott <abbotti at mev.co.uk>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> ---
>   drivers/staging/comedi/drivers/ii_pci20kc.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/comedi/drivers/ii_pci20kc.c b/drivers/staging/comedi/drivers/ii_pci20kc.c
> index 4d3f89c..6e2ce93 100644
> --- a/drivers/staging/comedi/drivers/ii_pci20kc.c
> +++ b/drivers/staging/comedi/drivers/ii_pci20kc.c
> @@ -146,6 +146,7 @@ static int ii20k_ao_insn_write(struct comedi_device *dev,
>   {
>   	void __iomem *iobase = ii20k_module_iobase(dev, s);
>   	unsigned int chan = CR_CHAN(insn->chanspec);
> +	unsigned int range = CR_RANGE(insn->chanspec);
>   	int i;
>
>   	for (i = 0; i < insn->n; i++) {
> @@ -153,9 +154,9 @@ static int ii20k_ao_insn_write(struct comedi_device *dev,
>
>   		s->readback[chan] = val;
>
> -		/* munge data */
> -		val += ((s->maxdata + 1) >> 1);
> -		val &= s->maxdata;
> +		/* munge the offset binary to 2's complement if needed */
> +		if (comedi_range_is_bipolar(s, range))
> +			val = comedi_offset_munge(s, val);
>
>   		writeb(val & 0xff, iobase + II20K_AO_LSB_REG(chan));
>   		writeb((val >> 8) & 0xff, iobase + II20K_AO_MSB_REG(chan));
>

I'm not sure about that as there are discrepancies in the manual.  The 
one I found was at:

https://www.uni-due.de/~hp0259/agwiki/lib/exe/fetch.php?media=anleitungen:pci-20006m.pdf

In "5. Specifications" it has:

CODE
	UNIPOLAR		Binary
	BIPOLAR			Complementary Binary

But then under "D/A Codes" it has:

OUTDATA		Volts Unipolar		Volts Bipolar
-------		--------------		-------------
32767		+Full Scale		-1 LSB *
0		+½ Full Scale		0
-1		+½ F.S. - 1 LSB		-1 LSB
-32768		0       		-Full Scale

± 5V Range: OUTDATA = VOLTS * (65536 / 10)
± 10V Range: OUTDATA = VOLTS * (65536 / 20)
0 to 10V Range: OUTDATA = (VOLTS * (65536 / 10)) - 32768

* I think that's a typo and should be "+Full Scale - 1 LSB".

The table (with typo corrected) and formulae indicate that for both 
unipolar and bipolar, -32768 is the lowest voltage and +32767 is the 
highest voltage, so we should munge comedi sample values regardless of 
range.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti at mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-