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