SamyGO

Does anybody have an idea how to check if Main Menu is on, MediaPlay is on, teletext(videotext) is on...? In general, how to determine what is displayed on the screen? Are there any registers found in exeDSP or RAM memory cells that might tell us what is our TV doing right now?

This knowledge will be useful for creating better external applications.
For example, PVR application must block some remote control buttons because their actions produce conflicts with PVR OSD. If PVR knew teletext is on, it would not draw REC icon that time and could draw it later, when a user leaves teletext mode.

Good question.
For mode selection there must be a register - variable. I think you can locate it by following one of the key-press functions, but this will be require gdb debugging of exeDSP.

Your idea is nice. Not too easy but worth to try.

Just another idea:
...or maybe we could make RAM-to-file snap-shot before- and after entering any mode and then compare them? But how to make RAM snapshot without getting coredump? It would be nice if exeDSP will hold all its variables in one continuous memory space. Then we could make a snapshot of this area only.

I don't find your idea useful. You think that its only channel mode will changed. But there is much more registers will be changed in every microsecconds.
So it's nearly impossible to find a memory location that changed by mode change. It requires thousands of snapshot and need data mining on them. Even with it, you might have nothing but air...
gdb way might be little hard but much more easier than inspecting whole memory from it's snapshots.
Also you cannot know the variable name from memory change easily, right?.