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staging: comedi: multiq3: tidy up multiq3_encoder_insn_read()

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Encoders are not a "normal" subdevice in comedi. For aesthetics, tidy
up this function and add a couple comments to clarify the function and
explain the strange munging of the data.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
H Hartley Sweeten 2015-10-05 15:33:17 -07:00 committed by Greg Kroah-Hartman
parent fc19858e1b
commit 47f1fa37db
1 changed files with 32 additions and 9 deletions
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41
drivers/staging/comedi/drivers/multiq3.c
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@ -185,22 +185,45 @@ static int multiq3_encoder_insn_read(struct comedi_device *dev,
struct comedi_insn *insn,
unsigned int *data)
{
int chan = CR_CHAN(insn->chanspec);
int value;
int n;
unsigned int chan = CR_CHAN(insn->chanspec);
unsigned int val;
int i;
for (n = 0; n < insn->n; n++) {
for (i = 0; i < insn->n; i++) {
/* select encoder channel */
multiq3_set_ctrl(dev, MULTIQ3_CTRL_EN |
MULTIQ3_CTRL_E_CHAN(chan));
/* reset the byte pointer */
outb(MULTIQ3_BP_RESET, dev->iobase + MULTIQ3_ENC_CTRL_REG);
/* latch the data */
outb(MULTIQ3_TRSFRCNTR_OL, dev->iobase + MULTIQ3_ENC_CTRL_REG);
value = inb(dev->iobase + MULTIQ3_ENC_DATA_REG);
value |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 8);
value |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 16);
data[n] = (value + 0x800000) & 0xffffff;
/* read the 24-bit encoder data (lsb/mid/msb) */
val = inb(dev->iobase + MULTIQ3_ENC_DATA_REG);
val |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 8);
val |= (inb(dev->iobase + MULTIQ3_ENC_DATA_REG) << 16);
/*
* Munge the data so that the reset value is in the middle
* of the maxdata range, i.e.:
*
* real value comedi value
* 0xffffff 0x7fffff 1 negative count
* 0x000000 0x800000 reset value
* 0x000001 0x800001 1 positive count
*
* It's possible for the 24-bit counter to overflow but it
* would normally take _quite_ a few turns. A 2000 line
* encoder in quadrature results in 8000 counts/rev. So about
* 1048 turns in either direction can be measured without
* an overflow.
*/
data[i] = (val + ((s->maxdata + 1) >> 1)) & s->maxdata;
}
return n;
return insn->n;
}
static void multiq3_encoder_reset(struct comedi_device *dev,