On Mon, Apr 16, 2007 at 12:14:27PM -0700, Matt Reimer wrote:
> On 4/15/07, Pavel Machek <[email protected]> wrote:
> > > + di->update_time = jiffies;
> > > +
> > > + /* DS2760 reports voltage in units of 4.88mV, but the battery class
> > > + * reports in units of mV, so convert by multiplying by 4.875.
> > > + * We approximate because integer math is cheap, and close enough.
> > */
> > > + di->voltage_raw = (di->raw[DS2760_VOLTAGE_MSB] << 3) |
> > > + (di->raw[DS2760_VOLTAGE_LSB] >> 5);
> > > + di->voltage_mV = (di->voltage_raw * 5) - (di->voltage_raw / 8);
> >
> > Hmm, not sure if such tricks re really worth it... should not compiler
> > be doing this?
>
> The shifts (<< 3 and >> 5) are just to get the bits reassembled in the
> right positions. The multiplication by 5 and subtracting 1/8 is
> because (AFAIK) we can't do floating point multiplication in the
> kernel. I'm open to suggestions.
Because we are in micro world now, divisions already replaced by
multiplication. I.e.
/* DS2760 reports voltage in units of 4.88mV, but the battery class
* reports in units of uV, so convert by multiplying by 4880. */
di->voltage_raw = (di->raw[DS2760_VOLTAGE_MSB] << 3) |
(di->raw[DS2760_VOLTAGE_LSB] >> 5);
di->voltage_uV = di->voltage_raw * 4880;
As a side effect, now we're not losing any precision. :-)
> > > + /* Calculate the empty level at the present temperature. */
> > > + scale[4] = di->raw[DS2760_ACTIVE_EMPTY + 4];
> > > + for (i = 3; i >= 0; i--)
> > > + scale[i] = scale[i + 1] + di->raw[DS2760_ACTIVE_EMPTY + i];
> > > +
> > > + di->empty_mAh = battery_interpolate(scale, di->temp_C / 10);
> >
> > Wow.
>
> Yeah, mea culpa. I don't like its obtuseness either, and haven't
> revisited it since I got it working. Basically the battery has an
> array stored in its EEPROM that represents the empty level at various
> temperature thresholds. What makes this complicated is that the array
> does not contain all absolute values; just the first is absolute, and
> the others are relative to it, in reverse order. The above code
> converts it to an array of absolute values from low to high. I'm open
> to suggestions about this one too.
By the way. Matt, you're more familiar with ds2760 specs, could you
enlighten me about "* 4" in this snippet?
> acr[0] = (di->full_active_mAh * 4) >> 8;
^^^
> acr[1] = (di->full_active_mAh * 4) & 0xff;
^^^
> if (w1_ds2760_write(di->w1_dev, acr,
> DS2760_CURRENT_ACCUM_MSB, 2) < 2)
> printk(KERN_ERR "ACR reset failed\n");
> Matt
Thanks!
--
Anton Vorontsov
email: [email protected]
backup email: [email protected]
irc://irc.freenode.org/bd2
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
