You fill in sim_instr do the instruction decoding and execution.
sim_load will typically take some input file and put it in memory.
cpu_reg should contain all machine state.
parse_sym/fprint_sym is to assemble (with DEPOSIT) and disassemble (EXAMINE-M) instructions.
sim_devices is an array of DEVICE * for peripherals. Something like
build_dev_tab will go through the array and initialize data structures
at run time.
Refer to this: https://github.com/open-simh/simh/blob/master/doc/simh.doc
Make use of asynchronous events. sim_activate posts a future event.
The "svc" routine will be called.
