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According to the datasheet, temperatures on the LM75 are kept in

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0.5 degC-precision the most-significant 9 bits of a 16-bit register.
Interpret them as such and simplify the conversion.
This commit is contained in:
briggs 2009-01-09 17:20:31 +00:00
parent 9a22d28e6e
commit 9ee13eae71
1 changed files with 10 additions and 18 deletions
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28
sys/dev/i2c/lm75.c
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@ -1,4 +1,4 @@
/* $NetBSD: lm75.c,v 1.19 2008/04/06 20:25:59 cegger Exp $ */
/* $NetBSD: lm75.c,v 1.20 2009/01/09 17:20:31 briggs Exp $ */
/*
* Copyright (c) 2003 Wasabi Systems, Inc.
@ -36,7 +36,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: lm75.c,v 1.19 2008/04/06 20:25:59 cegger Exp $");
__KERNEL_RCSID(0, "$NetBSD: lm75.c,v 1.20 2009/01/09 17:20:31 briggs Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@ -226,26 +226,18 @@ lmtemp_refresh(struct sysmon_envsys *sme, envsys_data_t *edata)
static uint32_t
lmtemp_decode_lm75(const uint8_t *buf)
{
int neg, temp;
int temp;
uint32_t val;
if (buf[0] & 1) {
/* Below 0C */
temp = ~buf[1] + 1;
neg = 1;
} else {
temp = buf[1];
neg = 0;
}
/*
* LM75 temps are the most-significant 9 bits of a 16-bit reg.
* sign-extend the MSB and add in the 0.5 from the LSB
*/
temp = (int8_t) buf[0];
temp = (temp << 1) + ((buf[1] >> 7) & 0x1);
/* Temp is given in 1/2 deg. C, we convert to uK. */
val = ((neg ? -temp : temp) / 2) * 1000000 + 273150000;
if (temp & 1) {
if (neg)
val -= 500000;
else
val += 500000;
}
val = temp * 500000 + 273150000;
return val;
}