On Fri, Mar 15, 2019 at 10:19:33AM +0000, Grönke, Christian wrote:
> Hello Guenter,
>
> > -----Ursprüngliche Nachricht-----
> > Von: Guenter Roeck <[email protected]> Im Auftrag von Guenter Roeck
> > Gesendet: Donnerstag, 14. März 2019 17:53
> > An: Grönke, Christian <[email protected]>
> > Cc: [email protected]
> > Betreff: Re: PMBus driver for FSP/3Y Power device with non-standard VOUT
> > values (LINEAR11 vs LINEAR16)
> >
> > Hi Christian,
> > On Thu, Mar 14, 2019 at 04:08:32PM +0000, Grönke, Christian wrote:
> > >
> > > The framework code seemed to work fine. I used your code for the
> > conversion:
> > > linear11 -> 'scaled integer' -> ieee754 It provided a way to test
> > > the code and was easy for me as my tries to do some other bit magic
> > > weren't successful. That means I partly tested the code from
> > > pmbus_data2reg_ieee754 as my read_word function uses this for the
> > > conversion. Of course not the module local function...
> > >
> >
> > Wondering ... I would have thought that it should be possible to
> > implement a simplified linear11 <--> ieee754 conversion, without
> > converting to a scaled integer first. Have you tried that ?
>
> There might be a more efficient and elegant way. I toyed around with
> the conversion for a moment but didn't figure out a working way
> quickly.
This should work.
u16 lin2ieee(u16 lin11)
{
s16 mantissa = ((s16)((lin11 & 0x7ff) << 5)) >> 5;
int exponent = (((s16)lin11) >> 11) + 25;
u16 sign = 0;
/* simple case */
if (mantissa == 0)
return 0;
if (mantissa < 0) {
sign = 0x8000;
mantissa = -mantissa;
}
while (mantissa < 0x400 && exponent > 1) {
mantissa <<= 1;
exponent--;
}
/* boundary checks */
if (exponent > 30)
return sign | 0x7bff;
if (mantissa < 0x400)
return sign | 0x0400;
return sign | (exponent << 10) | (mantissa & 0x3ff);
}
Guenter
