[DNX#2006040142000759] [U-Boot-Users] Bug in DTT for temperatures below z [...]

[DENX Support System]

Hello list,

inside the automatic U-Boot patch tracking system a new ticket
[DNX#2006040142000759] was created:

<snip>
> In message <42AFEBD3.3050008 at imc-berlin.de> you wrote:
> > 
> > there's a terrible bug in the current U-Boot CVS concerning DDT:
> > 
> > For temperature below zero the function dtt_get_temp() (at least for lm75) 
> > returns wrong values!
> > 
> > ...
> > DTT:   1 is 235 C
> > LCD:    Hitachi TX14D11 5,7" 320x240 TFT (235°C)
> > WDT:    disabled
> > 
> > This is because of the use of an "int" although the lm75 only returns two
> > byte ("signed short").
> 
> Ummm...
> 
> > This trivial fix is needed:
> 
> Wait a moment...
> 
> > --- u-boot/dtt/lm75.c   27 Jun 2003 21:32:38 -0000      1.2
> > +++ u-boot/dtt/lm75.c   15 Jun 2005 08:44:21 -0000
> > @@ -174,7 +170,7 @@
> > 
> >   int dtt_get_temp(int sensor)
> >   {
> > -    return (dtt_read(sensor, DTT_READ_TEMP) / 256);
> > +    return ( ((signed short) dtt_read(sensor, DTT_READ_TEMP)) / 256);
> 
> This is not the right way to fix it. I reject this patch.
> 
> dtt_read() is declared to return "int", so no  such  cast  should  be
> needed, i. e. you fix the symptoms instead of the cause.
> 
> 
> I think the patch must be done in dtt_read(); IMO the line
> 
> 	return ((int)((short)data[1] + (((short)data[0]) << 8)));
> 
> is wrong; it should read
> 
> 	return ((short)((short)data[1] + (((short)data[0]) << 8)));
> 
> or, even better,
> 
> 	short rc_s;
> 	...
> 	rc_s = (short)data[1] + (((short)data[0]) << 8);
> 	return (rc_s);
> 
> And the same problem is with dlen == 1 - it should read
> 
> 	return ((signed char)data[0]);
> 
> 
> Do you agree with this assessment? And can you please confirm that my
> suggested patch fixes your problem, too?
> 
> Best regards,
> 
> Wolfgang Denk
> 
> -- 
> Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
> Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
> Of all possible committee reactions to any  given  agenda  item,  the
> reaction  that will occur is the one which will liberate the greatest
> amount of hot air.                                -- Thomas L. Martin
> 
> 
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</snip>

Your U-Boot support team