#PROCHOT¶

The LM93 can monitor two #PROCHOT signals. The results are found in thesysfs files prochot1, prochot2, prochot1_avg, prochot2_avg, prochot1_max,and prochot2_max. prochot1_max and prochot2_max contain the user limitsfor #PROCHOT1 and #PROCHOT2, respectively. prochot1 and prochot2 containthe current readings for the most recent complete time interval. Thevalue of prochot1_avg and prochot2_avg is something like a 2 periodexponential moving average (but not quite - check the datasheet). Notethat this third value is calculated by the chip itself. All values rangefrom 0-255 where 0 indicates no throttling, and 255 indicates > 99.6%.

The monitoring intervals for the two #PROCHOT signals is also configurable.These intervals can be found in the sysfs files prochot1_interval andprochot2_interval. The values in these files specify the intervals for#P1_PROCHOT and #P2_PROCHOT, respectively. Selecting a value not in thislist will cause the driver to use the next largest interval. The availableintervals are (in seconds):

#PROCHOT intervals:

0.73, 1.46, 2.9, 5.8, 11.7, 23.3, 46.6, 93.2, 186, 372

It is possible to configure the LM93 to logically short the two #PROCHOTsignals. I.e. when #P1_PROCHOT is asserted, the LM93 will automaticallyassert #P2_PROCHOT, and vice-versa. This mode is enabled by writing anon-zero integer to the sysfs file prochot_short.

The LM93 can also override the #PROCHOT pins by driving a PWM signal ontoone or both of them. When overridden, the signal has a period of 3.56 ms,a minimum pulse width of 5 clocks (at 22.5kHz => 6.25% duty cycle), anda maximum pulse width of 80 clocks (at 22.5kHz => 99.88% duty cycle).

The sysfs files prochot1_override and prochot2_override contain booleanintegers which enable or disable the override function for #P1_PROCHOT and#P2_PROCHOT, respectively. The sysfs file prochot_override_duty_cyclecontains a value controlling the duty cycle for the PWM signal used whenthe override function is enabled. This value ranges from 0 to 15, with 0indicating minimum duty cycle and 15 indicating maximum.

#VRD_HOT¶

The LM93 can monitor two #VRD_HOT signals. The results are found in thesysfs files vrdhot1 and vrdhot2. There is one value per file: a boolean forwhich 1 indicates #VRD_HOT is asserted and 0 indicates it is negated. Thesefiles are read-only.

Smart Tach Mode (from the datasheet):

If a fan is driven using a low-side drive PWM, the tachometeroutput of the fan is corrupted. The LM93 includes smart tachometercircuitry that allows an accurate tachometer reading to beachieved despite the signal corruption.  In smart tach mode allfour signals are measured within 4 seconds.

Smart tach mode is enabled by the driver by writing 1 or 2 (associating thefan tachometer with a pwm) to the sysfs file fan<n>_smart_tach. A zerowill disable the function for that fan. Note that Smart tach mode cannot beenabled if the PWM output frequency is 22500 Hz (see below).

Manual PWM¶

The LM93 has a fixed or override mode for the two PWM outputs (although, thereare still some conditions that will override even this mode - see section15.10.6 of the datasheet for details.) The sysfs files pwm1_overrideand pwm2_override are used to enable this mode; each is a boolean integerwhere 0 disables and 1 enables the manual control mode. The sysfs files pwm1and pwm2 are used to set the manual duty cycle; each is an integer (0-255)where 0 is 0% duty cycle, and 255 is 100%. Note that the duty cycle valuesare constrained by the hardware. Selecting a value which is not availablewill cause the driver to use the next largest value. Also note: when manualPWM mode is disabled, the value of pwm1 and pwm2 indicates the current dutycycle chosen by the h/w.

PWM Output Frequency¶

The LM93 supports several different frequencies for the PWM output channels.The sysfs files pwm1_freq and pwm2_freq are used to select the frequency. Thefrequency values are constrained by the hardware. Selecting a value which isnot available will cause the driver to use the next largest value. Also notethat this parameter has implications for the Smart Tach Mode (see above).

PWM Output Frequencies (in Hz):

12, 36, 48, 60, 72, 84, 96, 22500 (default)

Automatic PWM¶

The LM93 is capable of complex automatic fan control, with many differentpoints of configuration. To start, each PWM output can be bound to anycombination of eight control sources. The final PWM is the largest of allindividual control sources to which the PWM output is bound.

The eight control sources are: temp1-temp4 (aka “zones” in the datasheet),#PROCHOT 1 & 2, and #VRDHOT 1 & 2. The bindings are expressed as a bitmaskin the sysfs files pwm<n>_auto_channels, where a “1” enables the binding, anda “0” disables it. The h/w default is 0x0f (all temperatures bound).

0x01	Temp 1
0x02	Temp 2
0x04	Temp 3
0x08	Temp 4
0x10	#PROCHOT 1
0x20	#PROCHOT 2
0x40	#VRDHOT 1
0x80	#VRDHOT 2

The function y = f(x) takes a source temperature x to a PWM output y. Thisfunction of the LM93 is derived from a base temperature and a table of 12temperature offsets. The base temperature is expressed in degrees C in thesysfs files temp<n>_auto_base. The offsets are expressed in cumulativedegrees C, with the value of offset <i> for temperature value <n> beingcontained in the file temp<n>_auto_offset<i>. E.g. if the base temperatureis 40C:

offset #	temp<n>_auto_offset<i>	range	pwm
1	0		25.00%
2	0		28.57%
3	1	40C - 41C	32.14%
4	1	41C - 42C	35.71%
5	2	42C - 44C	39.29%
6	2	44C - 46C	42.86%
7	2	48C - 50C	46.43%
8	2	50C - 52C	50.00%
9	2	52C - 54C	53.57%
10	2	54C - 56C	57.14%
11	2	56C - 58C	71.43%
12	2	58C - 60C	85.71%
		> 60C	100.00%

Valid offsets are in the range 0C <= x <= 7.5C in 0.5C increments.

There is an independent base temperature for each temperature channel. Note,however, there are only two tables of offsets: one each for temp[12] andtemp[34]. Therefore, any change to e.g. temp1_auto_offset<i> will alsoaffect temp2_auto_offset<i>.

The LM93 can also apply hysteresis to the offset table, to prevent unwantedoscillation between two steps in the offsets table. These values are found inthe sysfs files temp<n>_auto_offset_hyst. The value in this file has thesame representation as in temp<n>_auto_offset<i>.

If a temperature reading falls below the base value for that channel, the LM93will use the minimum PWM value. These values are found in the sysfs filestemp<n>_auto_pwm_min. Note, there are only two minimums: one each for temp[12]and temp[34]. Therefore, any change to e.g. temp1_auto_pwm_min will alsoaffect temp2_auto_pwm_min.

PWM Spin-Up Cycle¶

A spin-up cycle occurs when a PWM output is commanded from 0% duty cycle tosome value > 0%. The LM93 supports a minimum duty cycle during spin-up. Thesevalues are found in the sysfs files pwm<n>_auto_spinup_min. The value in thisfile has the same representation as other PWM duty cycle values. Theduration of the spin-up cycle is also configurable. These values are found inthe sysfs files pwm<n>_auto_spinup_time. The value in this file isthe spin-up time in seconds. The available spin-up times are constrained bythe hardware. Selecting a value which is not available will cause the driverto use the next largest value.

Spin-up Durations:

0 (disabled, h/w default), 0.1, 0.25, 0.4, 0.7, 1.0, 2.0, 4.0

#PROCHOT and #VRDHOT PWM Ramping¶

If the #PROCHOT or #VRDHOT signals are asserted while bound to a PWM outputchannel, the LM93 will ramp the PWM output up to 100% duty cycle in discretesteps. The duration of each step is configurable. There are two files, withone value each in seconds: pwm_auto_prochot_ramp and pwm_auto_vrdhot_ramp.The available ramp times are constrained by the hardware. Selecting a valuewhich is not available will cause the driver to use the next largest value.

Ramp Times:

0 (disabled, h/w default) to 0.75 in 0.05 second intervals

Fan Boost¶

For each temperature channel, there is a boost temperature: if the channelexceeds this limit, the LM93 will immediately drive both PWM outputs to 100%.This limit is expressed in degrees C in the sysfs files temp<n>_auto_boost.There is also a hysteresis temperature for this function: after the boostlimit is reached, the temperature channel must drop below this value beforethe boost function is disabled. This temperature is also expressed in degreesC in the sysfs files temp<n>_auto_boost_hyst.

GPIO Pins¶

The LM93 can monitor the logic level of four dedicated GPIO pins as well as thefour tach input pins. GPIO0-GPIO3 correspond to (fan) tach 1-4, respectively.All eight GPIOs are read by reading the bitmask in the sysfs file gpio. TheLSB is GPIO0, and the MSB is GPIO7.