I see that M.E.S.S. MC-1000's SOUND command doesn't work. The emulation halts. The following sample program should produce a continuous siren-like sound:
10 TEMPO 150,2,1
20 SOUND 87,15,1
30 SOUND 96,15,1
40 GOTO 20

The SOUND command depends on Z80's interrupt. In the list of TODOs there is:
   16     - interrupt from NE555

What do you mean by that? To copy the interrupt solution from another computer? (I can't find any "ne555" under /machine or /driver.