Everything was fine with the pedal input until...

[el-dr]

... the protected chips arrived. Since then it behaves totally unpredictably, often starts vomiting tons of foot controller messages, then suddenly stops it, sometimes it stays in a half open state on power up, even with no pedal connected. I don't use a hihat controller, so nothing is connected to this input.

First I thought something went wrong with the connections when I opened the case to replace the old Atmega, so I reopened it and checked the wires for damaged soldering. Nothing. It was the same even when I completely removed the ribbon cable from the input connector.

Then I put the old Atmega back (with a 200907xx firmware): everything worked fine again.

The only way I found to stop this was to connect an inverted polarity Roland sustain pedal to the input. When the hh input stays in a half open state on power up (continuously emitting CC data), I step on and release the pedal. This usually helps (not always, though).

I have a switch between Low and High pedal inputs and tried both settings, but none of them was more stable than the other.

I have 2 56 input MDs (Synthex 3.1) and they both behave the same way.

[Firelord]

Well, my MegaDrum always starts with the pedal indicator almost open and sometimes emits a lot of FC messages. I thought it might have something to do with some fault in my wiring. When I connect a simple foot controller (which consists of a normally open switch) and press/unpress it the indicator shows the pedal to be closed and everything is back to normal.

[dmitri]

Since you don't use a pedal and don't connect anything to the pedal input, with the default settings it may behave like this.
Set LevelsAuto to No and both High and Low levels below ~100 so that MegaDrum thinks that the pedal is always de-pressed.

[el-dr]

When I connect a simple foot controller (which consists of a normally open switch) and press/unpress it the indicator shows the pedal to be closed and everything is back to normal.

That's exactly what I noticed, but this was not present in earlier firmwares at all. My unprotected Atmega has a version from last July and it never does this.

[dmitri]

I've changed HiHat pedal handling since last July which resulted in a behaviour of an unconfigured/unconnected HiHat pedal input.

[el-dr]

I've changed HiHat pedal handling since last July which resulted in a behaviour of an unconfigured/unconnected HiHat pedal input.

What made it necessary to make an unused pedal input transmit MIDI and not to be interpreted as fully open?

[dmitri]

I've changed HiHat pedal handling since last July which resulted in a behaviour of an unconfigured/unconnected HiHat pedal input.

What made it necessary to make an unused pedal input transmit MIDI and not to be interpreted as fully open?

By default the HiHat pedal input is set in such a way that it expects a pedal to be connected, which is a more common way of using MegaDrum, so that after a few presses MegaDrum auto-updates High/Low levels to some initial usable values.
If the pedal is not connected, this auto-update algorithm will not have enough signal variation to work properly so manual configuration is required.

In general, auto configuration algorithms in MegaDrum, be it pedal High/Low levels or pads' HighLevels, are there to help in finding sane initial values but I've always advised to turn them off after using it for initial setup and use manual configuration for fine tuning.

[el-dr]

I set HiLvlAuto off on all inputs including the HH and tried various settings on the pedal input with no luck.

[dmitri]

I set HiLvlAuto off on all inputs including the HH and tried various settings on the pedal input with no luck.

HiLvlAuto on pads inputs, including the HiHat input, has nothing to do with LevelsAuto in the HiHat pedal settings.

[el-dr]

Sorry, I meant I disabled all automated settings on every input, including LevelsAuto on the HH input. Now I managed stop the random transmission of CC messages by plugging in a sustain pedal, but the pedal's state still changes without any reason: I look at the LCD from time to time and it keeps changing between open and half open position (while the pedal is lying on the floor untouched). Stepping on the pedal helps to get back to the open state, but I noticed that closing the switch doesn't always produce a closed state: it stays half open instead and then goes back to the open position when the pedal gets released.