EMU - Energy Management Unit#

EMU_BODMode_TypeDef#

EMU_BODMode_TypeDef

BOD threshold setting selector, active or inactive mode.

EMU_EM4State_TypeDef#

EMU_EM4State_TypeDef

EM4 modes.

EMU_EM4PinRetention_TypeDef#

EMU_EM4PinRetention_TypeDef

EM4 Pin Retention Type.

EMU_PowerConfig_TypeDef#

EMU_PowerConfig_TypeDef

Power configurations.

DCDC-to-DVDD is currently the only supported mode.

EMU_DcdcMode_TypeDef#

EMU_DcdcMode_TypeDef

DCDC operating modes.

EMU_DcdcModeEM23_TypeDef#

EMU_DcdcModeEM23_TypeDef

DCDC operating modes in EM2 or EM3.

EMU_DcdcConductionMode_TypeDef#

EMU_DcdcConductionMode_TypeDef

DCDC conduction modes.

EMU_DcdcAnaPeripheralPower_TypeDef#

EMU_DcdcAnaPeripheralPower_TypeDef

DCDC to DVDD mode analog peripheral power supply select.

EMU_DcdcLnRcoBand_TypeDef#

EMU_DcdcLnRcoBand_TypeDef

DCDC Low-noise RCO band select.

EMU_DcdcLnCompCtrl_TypeDef#

EMU_DcdcLnCompCtrl_TypeDef

DCDC Low Noise Compensator Control register.

EMU_VmonChannel_TypeDef#

EMU_VmonChannel_TypeDef

VMON channels.

EMU_VScaleEM01_TypeDef#

EMU_VScaleEM01_TypeDef

Supported EM0/1 Voltage Scaling Levels.

EMU_VScaleEM23_TypeDef#

EMU_VScaleEM23_TypeDef

Supported EM2/3 Voltage Scaling Levels.

EMU_VScaleEM4H_TypeDef#

EMU_VScaleEM4H_TypeDef

Supported EM4H Voltage Scaling Levels.

EMU_PeripheralRetention_TypeDef#

EMU_PeripheralRetention_TypeDef

Peripheral EM2 and 3 retention control.

EMU_DcdcLnReverseCurrentControl_TypeDef#

typedef int16_t EMU_DcdcLnReverseCurrentControl_TypeDef

DCDC Forced CCM and reverse current limiter control.

Positive values have unit mA.

EMU_EM01Init#

void EMU_EM01Init (const EMU_EM01Init_TypeDef * em01Init)

Update the EMU module with Energy Mode 0 and 1 configuration.

EMU_EM23Init#

void EMU_EM23Init (const EMU_EM23Init_TypeDef * em23Init)

Update the EMU module with Energy Mode 2 and 3 configuration.

EMU_EM23PresleepHook#

void EMU_EM23PresleepHook (void )

Energy mode 2/3 pre-sleep hook function.

This function is called by EMU_EnterEM2() and EMU_EnterEM3() functions just prior to execution of the WFI instruction. The function implementation does not perform anything, but it is SL_WEAK so that it can be re- implemented in application code if actions are needed.

EMU_EM23PostsleepHook#

void EMU_EM23PostsleepHook (void )

Energy mode 2/3 post-sleep hook function.

This function is called by EMU_EnterEM2() and EMU_EnterEM3() functions just after wakeup from the WFI instruction. The function implementation does not perform anything, but it is SL_WEAK so that it can be re- implemented in application code if actions are needed.

EMU_EFPEM23PresleepHook#

void EMU_EFPEM23PresleepHook (void )

EFP's Energy mode 2/3 pre-sleep hook function.

This function is similar to EMU_EM23PresleepHook() but is reserved for EFP usage.

Note

• The function is primarily meant to be used in systems with EFP circuitry. (EFP = Energy Friendly Pmic (PMIC = Power Management IC)). In such systems there is a need to drive certain signals to EFP pins to notify about energy mode transitions.

EMU_EFPEM23PostsleepHook#

void EMU_EFPEM23PostsleepHook (void )

EFP's Energy mode 2/3 post-sleep hook function.

This function is similar to EMU_EM23PostsleepHook() but is reserved for EFP usage.

Note

• The function is primarily meant to be used in systems with EFP circuitry. (EFP = Energy Friendly Pmic (PMIC = Power Management IC)). In such systems there is a need to drive certain signals to EFP pins to notify about energy mode transitions.

EMU_EnterEM2#

void EMU_EnterEM2 (bool restore)

Enter energy mode 2 (EM2).

When entering EM2, high-frequency clocks are disabled, i.e., HFXO, HFRCO and AUXHFRCO (for AUXHFRCO, see exception note below). When re-entering EM0, HFRCO is re-enabled and the core will be clocked by the configured HFRCO band. This ensures a quick wakeup from EM2.

However, prior to entering EM2, the core may have been using another oscillator than HFRCO. The restore parameter gives the user the option to restore all HF oscillators according to state prior to entering EM2, as well as the clock used to clock the core. This restore procedure is handled by SW. However, since handled by SW, it will not be restored before completing the interrupt function(s) waking up the core!

Note

• If restoring core clock to use the HFXO oscillator, which has been disabled during EM2 mode, this function will stall until the oscillator has stabilized. Stalling time can be reduced by adding interrupt support detecting stable oscillator, and an asynchronous switch to the original oscillator. See CMU documentation. Such a feature is however outside the scope of the implementation in this function.

• If ERRATA_FIX_EMU_E110_ENABLE is active, the core's SLEEPONEXIT feature can not be used.

• This function is incompatible with the Power Manager module. When the Power Manager module is present, it must be the one deciding at which EM level the device sleeps to ensure the application properly works. Using both at the same time could lead to undefined behavior in the application.

• If HFXO is re-enabled by this function, and NOT used to clock the core, this function will not wait for HFXO to stabilize. This must be considered by the application if trying to use features relying on that oscillator upon return.

• If a debugger is attached, the AUXHFRCO will not be disabled if enabled upon entering EM2. It will thus remain enabled when returning to EM0 regardless of the restore parameter.

• If HFXO autostart and select is enabled by using CMU_HFXOAutostartEnable(), the automatic starting and selecting of the core clocks will be done, regardless of the restore parameter, when waking up on the wakeup sources corresponding to the autostart and select setting.

• If voltage scaling is supported, the restore parameter is true and the EM0 voltage scaling level is set higher than the EM2 level, then the EM0 level is also restored.

• On Series 2 Config 2 devices (EFRxG22), this function will also relock the DPLL if the DPLL is used and restore is true.

Note that the hardware will automatically update the HFRCO frequency in the case where voltage scaling is used in EM2/EM3 and not in EM0/EM1. When the restore argument to this function is true then software will restore the original HFRCO frequency after EM2/EM3 wake up. If the restore argument is false then the HFRCO frequency is 19 MHz when coming out of EM2/EM3 and all wait states are at a safe value.

• The restore option should only be used if all clock control is done via the CMU API.

EMU_EnterEM3#

void EMU_EnterEM3 (bool restore)

Enter energy mode 3 (EM3).

When entering EM3, the high-frequency clocks are disabled by hardware, i.e., HFXO, HFRCO, and AUXHFRCO (for AUXHFRCO, see exception note below). In addition, the low-frequency clocks, i.e., LFXO and LFRCO are disabled by software. When re-entering EM0, HFRCO is re-enabled and the core will be clocked by the configured HFRCO band. This ensures a quick wakeup from EM3.

However, prior to entering EM3, the core may have been using an oscillator other than HFRCO. The restore parameter gives the user the option to restore all HF/LF oscillators according to state prior to entering EM3, as well as the clock used to clock the core. This restore procedure is handled by software. However, since it is handled by software, it will not be restored before completing the interrupt function(s) waking up the core!

Note

• If restoring core clock to use an oscillator other than HFRCO, this function will stall until the oscillator has stabilized. Stalling time can be reduced by adding interrupt support detecting stable oscillator, and an asynchronous switch to the original oscillator. See CMU documentation. This feature is, however, outside the scope of the implementation in this function.

• If ERRATA_FIX_EMU_E110_ENABLE is active, the core's SLEEPONEXIT feature can't be used.

• This function is incompatible with the Power Manager module. When the Power Manager module is present, it must be the one deciding at which EM level the device sleeps to ensure the application properly works. Using both at the same time could lead to undefined behavior in the application.

• If HFXO/LFXO/LFRCO are re-enabled by this function, and NOT used to clock the core, this function will not wait for those oscillators to stabilize. This must be considered by the application if trying to use features relying on those oscillators upon return.

• If a debugger is attached, the AUXHFRCO will not be disabled if enabled upon entering EM3. It will, therefore, remain enabled when returning to EM0 regardless of the restore parameter.

• If voltage scaling is supported, the restore parameter is true and the EM0 voltage scaling level is set higher than the EM3 level, then the EM0 level is also restored.

• On Series 2 Config 2 devices (EFRxG22), this function will also relock the DPLL if the DPLL is used and restore is true.

• The restore option should only be used if all clock control is done via the CMU API.

EMU_Save#

void EMU_Save (void )

Save the CMU HF clock select state, oscillator enable, and voltage scaling (if available) before EMU_EnterEM2() or EMU_EnterEM3() are called with the restore parameter set to false.

Calling this function is equivalent to calling EMU_EnterEM2() or EMU_EnterEM3() with the restore parameter set to true, but it allows the state to be saved without going to sleep. The state can be restored manually by calling EMU_Restore().

EMU_Restore#

void EMU_Restore (void )

Restore CMU HF clock select state, oscillator enable, and voltage scaling (if available) after EMU_EnterEM2() or EMU_EnterEM3() are called with the restore parameter set to false.

Calling this function is equivalent to calling EMU_EnterEM2() or EMU_EnterEM3() with the restore parameter set to true, but it allows the application to evaluate the wakeup reason before restoring state.

EMU_EM4Init#

void EMU_EM4Init (const EMU_EM4Init_TypeDef * em4Init)

Update the EMU module with Energy Mode 4 configuration.

EMU_EM4PresleepHook#

void EMU_EM4PresleepHook (void )

Energy mode 4 pre-sleep hook function.

This function is called by EMU_EnterEM4() just prior to the sequence of writes to put the device in EM4. The function implementation does not perform anything, but it is SL_WEAK so that it can be re-implemented in application code if actions are needed.

EMU_EFPEM4PresleepHook#

void EMU_EFPEM4PresleepHook (void )

EFP's Energy mode 4 pre-sleep hook function.

This function is similar to EMU_EM4PresleepHook() but is reserved for EFP usage.

Note

• The function is primarily meant to be used in systems with EFP circuitry. (EFP = Energy Friendly Pmic (PMIC = Power Management IC)). In such systems there is a need to drive certain signals to EFP pins to notify about energy mode transitions.

EMU_EnterEM4#

void EMU_EnterEM4 (void )

Enter energy mode 4 (EM4).

Note

• Only a power on reset or external reset pin can wake the device from EM4.

EMU_EnterEM4Wait#

void EMU_EnterEM4Wait (void )

Enter energy mode 4 (EM4).

This function waits after the EM4 entry request to make sure the CPU is properly shutdown or the EM4 entry failed.

Note

• Only a power on reset or external reset pin can wake the device from EM4.

EMU_EnterEM4H#

void EMU_EnterEM4H (void )

Enter energy mode 4 hibernate (EM4H).

Note

• Retention of clocks and GPIO in EM4 can be configured using EMU_EM4Init before calling this function.

EMU_EnterEM4S#

void EMU_EnterEM4S (void )

Enter energy mode 4 shutoff (EM4S).

Note

• Retention of clocks and GPIO in EM4 can be configured using EMU_EM4Init before calling this function.

EMU_MemPwrDown#

void EMU_MemPwrDown (uint32_t blocks)

Power down memory block.

Note

• Only a POR reset can power up the specified memory block(s) after power down.

EMU_RamPowerDown#

void EMU_RamPowerDown (uint32_t start, uint32_t end)

Power down RAM memory blocks.

This function will power down all the RAM blocks that are within a given range. The RAM block layout is different between device families, so this function can be used in a generic way to power down a RAM memory region which is known to be unused.

This function will only power down blocks which are completely enclosed by the memory range given by [start, end).

This is an example to power down all RAM blocks except the first one. The first RAM block is special in that it cannot be powered down by the hardware. The size of the first RAM block is device-specific. See the reference manual to find the RAM block sizes.

EMU_RamPowerDown(SRAM_BASE, SRAM_BASE + SRAM_SIZE);

Note

• Only a reset can power up the specified memory block(s) after power down on a series 0 device. The specified memory block(s) will stay off until a call to EMU_RamPowerUp() is done on series 1/2.

EMU_RamPowerUp#

void EMU_RamPowerUp (void )

Power up all available RAM memory blocks.

This function will power up all the RAM blocks on a device, this means that the RAM blocks are retained in EM2/EM3. Note that this functionality is not supported on Series 0 devices. Only a reset will power up the RAM blocks on a series 0 device.

EMU_PeripheralRetention#

void EMU_PeripheralRetention (EMU_PeripheralRetention_TypeDef periMask, bool enable)

Set EM2 3 peripheral retention control.

Note

• Only peripheral retention disable is currently supported. Peripherals are enabled by default and can only be disabled.

EMU_UpdateOscConfig#

void EMU_UpdateOscConfig (void )

Update EMU module with CMU oscillator selection/enable status.

EMU_VScaleEM01ByClock#

void EMU_VScaleEM01ByClock (uint32_t clockFrequency, bool wait)

Voltage scale in EM0 and 1 by clock frequency.

Note

• This function is primarily needed by the CMU - Clock Management Unit.

EMU_VScaleEM01#

void EMU_VScaleEM01 (EMU_VScaleEM01_TypeDef voltage, bool wait)

Force voltage scaling in EM0 and 1 to a specific voltage level.

Note

• This function is useful for upscaling before programming Flash from MSC - Memory System Controller and downscaling after programming is done. Flash programming is only supported at emuVScaleEM01_HighPerformance.

• This function ignores vScaleEM01LowPowerVoltageEnable set from EMU_EM01Init().

EMU_DCDCModeSet#

void EMU_DCDCModeSet (EMU_DcdcMode_TypeDef dcdcMode)

Set DCDC regulator operating mode.

EMU_DCDCInit#

bool EMU_DCDCInit (const EMU_DCDCInit_TypeDef * dcdcInit)

Configure the DCDC regulator.

Note

• Do not call this function if the power circuit is configured for NODCDC as described in the Power Configurations section of the Reference Manual. Instead, call EMU_DCDCPowerOff().

Returns

• True if initialization parameters are valid.

EMU_DCDCPowerOff#

bool EMU_DCDCPowerOff (void )

Power off the DCDC regulator.

This function powers off the DCDC controller. This function should only be used if the external power circuit is wired for no DCDC. If the external power circuit is wired for DCDC usage, use EMU_DCDCInit() and set the DCDC in bypass mode to disable DCDC.

Returns

• Return false if the DCDC could not be disabled.

EMU_DCDCModeEM23Set#

void EMU_DCDCModeEM23Set (EMU_DcdcModeEM23_TypeDef dcdcModeEM23)

Set DCDC Mode EM23 operating mode.

EMU_DCDCConductionModeSet#

void EMU_DCDCConductionModeSet (EMU_DcdcConductionMode_TypeDef conductionMode, bool rcoDefaultSet)

Set DCDC LN regulator conduction mode.

EMU_DCDCOutputVoltageSet#

bool EMU_DCDCOutputVoltageSet (uint32_t mV, bool setLpVoltage, bool setLnVoltage)

Set the DCDC output voltage.

Note

• The DCDC is not characterized for the entire valid output voltage range. For that reason an upper limit of 3.0V output voltage is enforced.

Returns

• True if the mV parameter is valid.

EMU_DCDCOptimizeSlice#

void EMU_DCDCOptimizeSlice (uint32_t em0LoadCurrentmA)

Optimize the DCDC slice count based on the estimated average load current in EM0.

EMU_DCDCLnRcoBandSet#

void EMU_DCDCLnRcoBandSet (EMU_DcdcLnRcoBand_TypeDef band)

Set DCDC Low-noise RCO band.

EMU_VmonInit#

void EMU_VmonInit (const EMU_VmonInit_TypeDef * vmonInit)

Initialize a VMON channel.

Initialize a VMON channel without hysteresis. If the channel supports separate rise and fall triggers, both thresholds will be set to the same value. The threshold will be converted to a register field value based on calibration values from the DI page.

EMU_VmonHystInit#

void EMU_VmonHystInit (const EMU_VmonHystInit_TypeDef * vmonInit)

Initialize a VMON channel with hysteresis (separate rise and fall triggers).

Initialize a VMON channel which supports hysteresis. The AVDD channel is the only channel to support separate rise and fall triggers. The rise and fall thresholds will be converted to a register field value based on the calibration values from the DI page.

EMU_VmonEnable#

void EMU_VmonEnable (EMU_VmonChannel_TypeDef channel, bool enable)

Enable or disable a VMON channel.

EMU_VmonChannelStatusGet#

bool EMU_VmonChannelStatusGet (EMU_VmonChannel_TypeDef channel)

Get the status of a voltage monitor channel.

Returns

• A status of the selected VMON channel. True if the channel is triggered.

EMU_TemperatureGet#

float EMU_TemperatureGet (void )

Get temperature in degrees Celsius.

Returns

• Temperature in degrees Celsius

EMU_LDOStatusGet#

bool EMU_LDOStatusGet (void )

Check status of the internal LDO regulator.

Returns

• Return true if the regulator is on, false if regulator is off.

EMU_EnterEM1#

void EMU_EnterEM1 (void )

Enter energy mode 1 (EM1).

Note

• This function is incompatible with the Power Manager module. When the Power Manager module is present, it must be the one deciding at which EM level the device sleeps to ensure the application properly works. Using both at the same time could lead to undefined behavior in the application.

EMU_VScaleWait#

void EMU_VScaleWait (void )

Wait for voltage scaling to complete.

EMU_VScaleGet#

EMU_VScaleEM01_TypeDef EMU_VScaleGet (void )

Get current voltage scaling level.

Returns

• Current voltage scaling level.

EMU_VmonStatusGet#

bool EMU_VmonStatusGet (void )

Get the status of the voltage monitor (VMON).

Returns

• Status of the VMON. True if all the enabled channels are ready, false if one or more of the enabled channels are not ready.

EMU_IntClear#

void EMU_IntClear (uint32_t flags)

Clear one or more pending EMU interrupts.

EMU_IntDisable#

void EMU_IntDisable (uint32_t flags)

Disable one or more EMU interrupts.

EMU_IntEnable#

void EMU_IntEnable (uint32_t flags)

Enable one or more EMU interrupts.

Note

• Depending on the use, a pending interrupt may already be set prior to enabling the interrupt. To ignore a pending interrupt, consider using EMU_IntClear() prior to enabling the interrupt.

EMU_IntGet#

uint32_t EMU_IntGet (void )

Get pending EMU interrupt flags.

Note

• Event bits are not cleared by the use of this function.

Returns

• EMU interrupt sources pending. Returns one or more valid interrupt flags for the EMU module (EMU_IF_nnn).

EMU_IntGetEnabled#

uint32_t EMU_IntGetEnabled (void )

Get enabled and pending EMU interrupt flags.

Useful for handling more interrupt sources in the same interrupt handler.

Note

• Interrupt flags are not cleared by the use of this function.

Returns

• Pending and enabled EMU interrupt sources Return value is the bitwise AND of

  • the enabled interrupt sources in EMU_IEN and

  • the pending interrupt flags EMU_IF.

EMU_IntSet#

void EMU_IntSet (uint32_t flags)

Set one or more pending EMU interrupts.

EMU_Lock#

void EMU_Lock (void )

Lock EMU registers in order to protect them against unintended modification.

Note

• If locking EMU registers, they must be unlocked prior to using any EMU API functions modifying EMU registers, excluding interrupt control and regulator control if the architecture has a EMU_PWRCTRL register. An exception to this is the energy mode entering API (EMU_EnterEMn()), which can be used when the EMU registers are locked.

EMU_Unlock#

void EMU_Unlock (void )

Unlock the EMU so that writing to locked registers again is possible.

EMU_PowerLock#

void EMU_PowerLock (void )

Lock the EMU regulator control registers in order to protect against unintended modification.

EMU_PowerUnlock#

void EMU_PowerUnlock (void )

Unlock the EMU power control registers so that writing to locked registers again is possible.

EMU_EM2Block#

void EMU_EM2Block (void )

Block entering EM2 or higher number energy modes.

EMU_EM2UnBlock#

void EMU_EM2UnBlock (void )

Unblock entering EM2 or higher number energy modes.

EMU_UnlatchPinRetention#

void EMU_UnlatchPinRetention (void )

When EM4 pin retention is set to emuPinRetentionLatch, then pins are retained through EM4 entry and wakeup.

The pin state is released by calling this function. The feature allows peripherals or GPIO to be re-initialized after EM4 exit (reset), and when initialization is done, this function can release pins and return control to the peripherals or GPIO.

EMU_TemperatureReady#

bool EMU_TemperatureReady (void )

Temperature measurement ready status.

Returns

• True if temperature measurement is ready

dcdcConstCalibrationLoad#

static bool dcdcConstCalibrationLoad (void )

Load DCDC calibration constants from the DI page.

A constant means that calibration data that does not change depending on other configuration parameters.

Returns

• False if calibration registers are locked.

dcdcValidatedConfigSet#

static void dcdcValidatedConfigSet (void )

Set recommended and validated current optimization and timing settings.

currentLimitersUpdate#

static void currentLimitersUpdate (void )

Compute current limiters: LNCLIMILIMSEL: LN current limiter threshold LPCLIMILIMSEL: LP current limiter threshold DCDCZDETCTRL: zero detector limiter threshold.

userCurrentLimitsSet#

static void userCurrentLimitsSet (uint32_t maxCurrent_mA, EMU_DcdcLnReverseCurrentControl_TypeDef reverseCurrentControl)

Set static variables that hold the user set maximum peak current and reverse current.

Update limiters.

compCtrlSet#

static void compCtrlSet (EMU_DcdcLnCompCtrl_TypeDef comp)

Set DCDC low noise compensator control register.

lpCmpHystCalibrationLoad#

static bool lpCmpHystCalibrationLoad (bool lpAttenuation, uint8_t lpCmpBias, dcdcTrimMode_TypeDef trimMode)

Load EMU_DCDCLPCTRL_LPCMPHYSSEL depending on LP bias, LP feedback attenuation, and DEVINFOREV.

lpGetDevinfoVrefLowHigh#

static void lpGetDevinfoVrefLowHigh (uint32_t * vrefL, uint32_t * vrefH, bool lpAttenuation, uint8_t lpcmpBias)

Load LPVREF low and high from DEVINFO.

vmonCalibratedThreshold#

static uint32_t vmonCalibratedThreshold (EMU_VmonChannel_TypeDef channel, int threshold)

Get the calibrated threshold value.

All VMON channels have two calibration fields in the DI page that describes the threshold at 1.86 V and 2.98 V. This function will convert the uncalibrated input voltage threshold in millivolts into a calibrated threshold.

Returns

• A calibrated threshold value to use. The first digit of the return value is placed in the "fine" register fields while the next digits are placed in the "coarse" register fields.

EMU_VSCALE_PRESENT#

#define EMU_VSCALE_PRESENT

Voltage scaling present.

EMU_VSCALE_EM01_PRESENT#

#define EMU_VSCALE_EM01_PRESENT

Voltage scaling for EM01 present.

EMU_SERIES1_DCDC_BUCK_PRESENT#

#define EMU_SERIES1_DCDC_BUCK_PRESENT

DC-DC buck converter present.

emuDcdcLnHighEfficiency#

#define emuDcdcLnHighEfficiency

-1

High efficiency mode.

EMU_DCDCZDETCTRL_ZDETILIMSEL is "don't care".

emuDcdcLnFastTransient#

#define emuDcdcLnFastTransient

160

Default reverse current for fast transient response mode (low noise).

EMU_EM01INIT_DEFAULT#

#define EMU_EM01INIT_DEFAULT

Default initialization of EM0 and 1 configuration.

EMU_EM23INIT_DEFAULT#

#define EMU_EM23INIT_DEFAULT

Default initialization of EM2 and 3 configuration.

EMU_EM4INIT_DEFAULT#

#define EMU_EM4INIT_DEFAULT

Default initialization of EM4 configuration (Series 1 with VSCALE).

EMU_DCDCINIT_DEFAULT#

#define EMU_DCDCINIT_DEFAULT

Default DCDC initialization.

EMU_VMONINIT_DEFAULT#

#define EMU_VMONINIT_DEFAULT

Default VMON initialization structure.

EMU_VMONHYSTINIT_DEFAULT#

#define EMU_VMONHYSTINIT_DEFAULT

Default VMON Hysteresis initialization structure.

EMU_TEMP_ZERO_C_IN_KELVIN#

#define EMU_TEMP_ZERO_C_IN_KELVIN

(273.15f)

Zero degrees Celcius in Kelvin.