Fanshim automatic.py preempt bug

@Steve wrote:

I think there’s a bug in autmatic.py

My output>

sudo python3 automatic.py --threshold 60 --hysteresis 10 --delay 1 --preempt --verbose
Current: 38.46 Target: 60.00 Freq 1.50 MaxFreq 1.50 Automatic: True On: False
Current: 38.46 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 38.95 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 37.97 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 38.95 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 37.97 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 39.43 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 37.97 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 38.46 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 38.46 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 38.46 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True
Current: 38.46 Target: 60.00 Freq 0.60 MaxFreq 1.50 Automatic: True On: True

From code

try:
update_led(fanshim.get_fan())
while True:
    t = get_cpu_temp()
    f = get_cpu_freq()
    if args.verbose:
        print("Current: {:05.02f} Target: {:05.02f} Freq {: 5.02f} MaxFreq {: 5.02f} Automatic: {} On: {}".format(t, args.threshold, f.current / 1000.0, f.max / 1000.0, armed, enabled))
    if abs(last_change - t) > args.hysteresis and armed:
        enable = (t >= args.threshold)
        if args.preempt:
            enable = enable or (int(f.current) == int(f.max))
        if set_fan(enable):
            last_change = t
    time.sleep(args.delay)

(this is your code, with one extra parameter for max frequency)

if abs(last_change - t) > args.hysteresis and armed:
must be true because enabled is evaluated so I presume
last_change is presumably 0, t is around 38, 0-38 is -38. Abs(-38) = 38. 38>10

Then
enable = (t >= args.threshold)
t=38, 38 is less than theshold (60), so enable is false.

preempt is true, so we move to this test
enable = enable or (int(f.current) == int(f.max))
enable is initially false on first pass. However initially there’s a processor surge when initially launching the program, so current frequency initially maxes max frequency.
enabled is turned on.
The fan switches on
last_change is set to current temp, around 38.

if abs(last_change - t) > args.hysteresis and armed:
will be never be true as the last temp and temp are around 38 and the difference will never exceed my hysteresis (10) so enabled will never re-evalute, so enabled will remain on for ever.

There is also a possibility that with a large hysteresis and a short interval, that the current code would never have a large enough temperature change to trigger a reevaluation of enabled.

I’ve taken the liberty to have a go at rewriting.
If preempt and running full speed, fan on.
If over temperature, fan on.
If under (temperature - hysteresis), fan off

https://pastebin.com/vc7U83C6

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