15-410 Simics Environment Guide

Invoking Simics

Most features of the Simics environment are controlled by knobs in the environment at time of invocation:

SIMICS_TEXT_CONSOLE

If this environment variable contains a nonempty string, Simics will spawn an xterm for a text console rather than its graphic console. This may speed simulations where the X display is remote. Because this console is low-fidelity, it is usable for the thread library and kernel projects, but not for the game project! Note that NUL bytes in video memory may lead to odd behavior on the text console which does not match the behavior on hardware (did we mention it's low-fidelity?).

SIMICS_CPU_COUNT

If the value of this environment variable can be converted to an integer, simics will attempt to run with that many CPUs. Results are not necessarily well behaved for values outside of 1 to 15.

SIMICS_AMD_SIXTYFOUR

If this environment variable is nonempty, Simics will instead simulate an amd64 ("hammer") system. The default is a Pentium 4 system.

SIMICS_REALTIME

If this environment variable is nonempty, Simics will watch the wall clock and attempt to keep the system elapsed time equal to the wall clock elapsed time, rather than allowing events to happen as fast as possible. This is generally only useful for simulations which are mostly idle, notably during Project 1.

SIMICS_DISK_IMAGE

Names a file to use as the backing store of the primary IDE bus's master disk.

SIMICS_DISK_SIZE

The size of the primary disk image

Adding Code To The Simics Environment

Disclaimer

On an only slightly less dire note, you should make an effort not to get lost in this. Simics is really, really big, and contains tons and tons of features, nooks, crannies, and traps. Remember that your objective is to write a 410 assignment, which is probably not a Simics module. This is intended as debugging tool, and like any tool, it should not be used when inappropriate. Moreover, as the power of this tool comes from its flexibility and therefore bestowes upon this tool a very steep learning curve, it should only be used when lesser tools are in some way inadequate for the job at hand.

Where do I do this

What do I do?

Adding a custom breakpoint

Breakpoint handler functions take four parameters:

arg	Per-HAP callback data, unused in the current 410 environment
obj	The configuration object which caused this breakpoint
brknum	The breakpoint number
m	The memory transaction associated with this breakpoint. See the Simics reference manual for more information.

Here's a way to add a breakpoint that stops only when the address it is watching takes on any of a set of values and traces all values except a specified set. It demos how to add breakpoints to the simulation environment within the breakpoint routing feature provided by the 410 environment.

single_address = 0x01234567             # Breakpoint address
watch_size = 4                          # Breakpoint size
trace_silence_values = [ 0x00c0ffee ]   # Don't show these values
break_on_values = [ 0xfeedface ]        # Stop the simulation on these values

def handle_my_breakpoint(arg, obj, brknum, m):
  # Filter out control messages
  if SIM_mem_op_is_control(m) :
    print "Custom breakpoint got a control transaction, ignoring!"
    return
  
  # Extract the CPU
  if not SIM_mem_op_is_from_cpu(m) :
    print "Custom breakpoint got a non-CPU initiator!"
    return
  cpu = m.ini_ptr
  
  ### This depends on 410 segmentation!  The correct way is, much like x86,
  ### a lot more putrid.
  pa = SIM_logical_to_physical(cpu, Sim_DI_Data, m.logical_address)
  
  # Get size of transaction or fall back
  size = m.size
  if size == 0 :
    print "WARNING: Zero size memory transaction is not a control transaction!"
    size = watch_size
  
  # Read out the current value at that physical address
  # which we assume to be a 32 bit value (thus the 4)
  cur_dat = SIM_read_phys_memory(cpu, pa, size)
  
  # Construct informative message
  str = "Custom breakpoint %d hit at l:0x%x with size %d, saw there %x" \
      % (brknum, m.logical_address, m.size, cur_dat)
  
  # If the value read matches our break-on value, then stop the world.
  if cur_dat in break_on_values :
    SIM_break_simulation(str)
  elif not cur_dat in trace_silence_values :
    print str

nbp = SIM_breakpoint(conf.primary_context,  # Watch the primary context
                      Sim_Break_Virtual,    # We're interested in Virtual addr
                      Sim_Access_Read,      # Read access
                      single_address,       # The address in question, above
                      watch_size,           # How big of an area are we watching?
                      Sim_Breakpoint_Simulation # This breakpoint is part of
                                                # the simulation environment.
                    )

# Register this with the 410mods-core.py breakpoint dispatch system
breakpoint_handlers[ nbp ] = handle_my_breakpoint

# Inform the user of our decision
print("Custom breakpoint registered on p:%x with break values %s as %d"
        % (single_address, break_on_values, nbp) )

[Last modified Friday February 25, 2022]