Commands are:
   s(tep <n>      Execute n (default 1) TM instructions
   g(o            Execute TM instructions until HALT
   r(egs          Print the contents of the registers
   i(Mem <b <n>>  Print n iMem locations starting at b
   d(Mem <b <n>>  Print n dMem locations starting at b
   t(race         Toggle instruction trace
   p(rint         Toggle print of total instructions executed ('go' only)
   c(lear         Reset simulator for new execution of program
   h(elp          Cause this list of commands to be printed
   q(uit          Terminate the simulation