[Macchiato] Fan control

[Matt Sealey]

That’s an interesting idea, I was kicking about the same sort of thing with
an RPi 2 - after I found that all the good fan/temp controllers lmsensors
supports on so-called “gaming motherboards” these days are actually a
Cortex-M0, I figured why not put a quad core A7 to the task? :)

It does have the irony of being able to boot the same kernel as the
macchiatobin if I swap in an RPi3.. I use one for ser2net at work, and I
doubt it would be too difficult to wire it to the TDM SPI or I2C port, flip
some boot switches and basically make it a $30 PROMjet as well :)

Most of the “good” infrastructure IC’s have a Cortex-M doing power
management and the 88F8040 is no exception - I wonder if PWM is actually a
function of setting the CP pin to GPIO and routing a CM3 local/PPB
peripheral to it - having it do even software PWM would be fantastic.

It’s a damn shame the best docs we have are Linux drivers/FDT source.

Ta,
Matt

On Fri, Apr 6, 2018 at 18:39 Stuart Monteith <stoo at stoo.me.uk> wrote:

> Hi,
> I’m in the process of experimenting with a microcontroller to turn the bin
> on and off. I was quite pleased to find that the TDM port’s I2C lines would
> recognise my Teensy-LC micro-controller speaking I2C. I’m currently
> studying the IPMI protocol as I’d like to drive and configure the
> microcontroller that way too. I was also thinking of hooking up the case
> fans to it too, but I haven’t come to any conclusion as to what to base the
> fan speeds.
>
> The microcontroller, so far, would be connected to the ATX power supply
> (GND, +5VSB, PSON), power switch, power LED, reset switch (in parallel with
> case switch), USB-serial to my server,  TDM for I2C control from the system
> itself. I reckon with a 5V line from ATX a fan or two could be connected.
> The reason why I’ve been wanting to do this was so that machine could shut
> itself down when my UPS was off the mains.
>
> BR,
>    Stuart
>
>
> Stuart Monteith
> stoo at stoo.me.uk
>
>
>
>
> On 6 Apr 2018, at 23:39, Matt Sealey <neko at bakuhatsu.net> wrote:
>
>
> Having software toggle a GPIO fast enough to effect PWM would be highly
> processor intensive. that would heat the package meaning running the fan
> faster, you’ll make yourself a nice feedback loop!
>
> There is a thermal diode and a way to calibrate and use it since U-Boot
> reports it and I can see the temp in sysfs (it reacts to the diode on my
> case fan speeding up the case fan and moving more air...).
>
> I’m just not sure you could do a lot with it just being a GPIO, the only
> clock-like function for that pin is the MDIO clock for one of the Ethernet
> PHYs - if you can prove that same clock is not exported, though, you could
> use clock management to do what you want. MDIO clocks aren’t fast though,
> so it may be the difference between full off, very slow rpm (if the fan
> supports that range of duty cycle) and full on, not a nice
> temperature-controlled swing.
>
>
>
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