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@xxxxxxxxxxxxxxxxxxx>
Cc: Ian Abbott <abbotti@xxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/comedi/drivers/multiq3.c | 41 +++++++++++++++++++++++++-------
1 file changed, 32 insertions(+), 9 deletions(-)
diff --git a/drivers/staging/comedi/drivers/multiq3.c b/drivers/staging/comedi/drivers/multiq3.c
index b5d2354..fa63637 100644
--- a/drivers/staging/comedi/drivers/multiq3.c
+++ b/drivers/staging/comedi/drivers/multiq3.c
@@ -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,
--
2.5.1
_______________________________________________
devel mailing list
devel@xxxxxxxxxxxxxxxxxxxxxx
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
