Commit 47f1fa37 authored by H Hartley Sweeten's avatar H Hartley Sweeten Committed by Greg Kroah-Hartman
Browse files

staging: comedi: multiq3: tidy up multiq3_encoder_insn_read() 



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: default avatarH Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fc19858e

drivers/staging/comedi/drivers/multiq3.c

+32 −9
Original line number Diff line number Diff line
@@ -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,