[U-Boot-Users] Bug in DTT for temperatures below zero degress !!!
wd at denx.de
Sun Mar 12 15:54:44 CET 2006
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").
> 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 + (((short)data) << 8)));
is wrong; it should read
return ((short)((short)data + (((short)data) << 8)));
or, even better,
rc_s = (short)data + (((short)data) << 8);
And the same problem is with dlen == 1 - it should read
return ((signed char)data);
Do you agree with this assessment? And can you please confirm that my
suggested patch fixes your problem, too?
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
More information about the U-Boot