qemu/hw/misc/tmp105.h
Peter Maydell ab135622cf tmp105: Correct handling of temperature limit checks
The TMP105 datasheet says that in Interrupt Mode (when TM==1) the device
signals an alert when the temperature equals or exceeds the T_high value and
then remains high until a device register is read or the device responds to
the SMBUS Alert Response address, or the device is put into Shutdown Mode.
Thereafter the Alert pin will only be re-signalled when temperature falls
below T_low; alert can then be cleared in the same set of ways, and the
device returns to its initial "alert when temperature goes above T_high"
mode. (If this textual description is confusing, see figure 3 in the
TI datasheet at https://www.ti.com/lit/gpn/tmp105 .)

We were misimplementing this as a simple "always alert if temperature is
above T_high or below T_low" condition, which gives a spurious alert on
startup if using the "T_high = 80 degrees C, T_low = 75 degrees C" reset
limit values.

Implement the correct (hysteresis) behaviour by tracking whether we
are currently looking for the temperature to rise over T_high or
for it to fall below T_low. Our implementation of the comparator
mode (TM==0) wasn't wrong, but rephrase it to match the way that
interrupt mode is now handled for clarity.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20201110150023.25533-3-peter.maydell@linaro.org
2020-11-17 12:56:33 +00:00

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/*
* Texas Instruments TMP105 Temperature Sensor
*
* Browse the data sheet:
*
* http://www.ti.com/lit/gpn/tmp105
*
* Copyright (C) 2012 Alex Horn <alex.horn@cs.ox.ac.uk>
* Copyright (C) 2008-2012 Andrzej Zaborowski <balrogg@gmail.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or
* later. See the COPYING file in the top-level directory.
*/
#ifndef QEMU_TMP105_H
#define QEMU_TMP105_H
#include "hw/i2c/i2c.h"
#include "hw/misc/tmp105_regs.h"
#include "qom/object.h"
#define TYPE_TMP105 "tmp105"
OBJECT_DECLARE_SIMPLE_TYPE(TMP105State, TMP105)
/**
* TMP105State:
* @config: Bits 5 and 6 (value 32 and 64) determine the precision of the
* temperature. See Table 8 in the data sheet.
*
* @see_also: http://www.ti.com/lit/gpn/tmp105
*/
struct TMP105State {
/*< private >*/
I2CSlave i2c;
/*< public >*/
uint8_t len;
uint8_t buf[2];
qemu_irq pin;
uint8_t pointer;
uint8_t config;
int16_t temperature;
int16_t limit[2];
int faults;
uint8_t alarm;
/*
* The TMP105 initially looks for a temperature rising above T_high;
* once this is detected, the condition it looks for next is the
* temperature falling below T_low. This flag is false when initially
* looking for T_high, true when looking for T_low.
*/
bool detect_falling;
};
#endif