Rhialto had the feature request to have a mode, where Xemu/MEGA65 can warn you
on reading memory which was not written before, can be useful to find ROM bugs.

In this current form, it's quite minimal and simple:

1. Only works on the first 126K of physical RAM
2. Only works from command line, start emulation with paramter: -ramcheckread
3. You need to watch the output of the emulator, so on UNIX-like/Linux/Mac systems,
   emulator should be started from terminal window, on Windows, Xemu
   console must be open (start also with parameter: -syscon)
4. Check the output of the emulator, you can find lines like:
   MEM: DEBUG: main RAM at linear address $101A0 has been read without prior write; PC=$8613 [$20613]
   The PC value can be off by some bytes, because it may have been
   incremented already during opcode emulation. The [...] is the linear
   address for the mentioned CPU PC value.

Well, that's it.

Incomplete and possible buggy first try implementation of DMA line
drawing. Ideas are based on a "draft implementation" by btoschi
on Discord (@bjotos on github).

The only reason I present this highly incomplete work in the next branch
of Xemu (so not in dev) because I am on holiday, so it's a bit random
when I have time to do more work. Thus it's better to release it in
this unfinished form, I guess, if someone wants to play with it.