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"""
This gem5 configuation script creates a simple board to run the first
10^6 ticks of "riscv-hello" binary simulation and saves a checkpoint.
This configuration serves as an example of taking a checkpoint.

This is setup is the close to the simplest setup possible using the gem5
library. It does not contain any kind of caching, IO, or any non-essential
components.

Usage
-----

```
scons build/RISCV/gem5.opt
./build/RISCV/gem5.opt \
    configs/example/gem5_library/checkpoint/riscv-hello-save-checkpoint.py
```
"""

from gem5.isas import ISA
from gem5.utils.requires import requires
from gem5.resources.resource import Resource
from gem5.components.memory import SingleChannelDDR3_1600
from gem5.components.processors.cpu_types import CPUTypes
from gem5.components.boards.simple_board import SimpleBoard
from gem5.components.cachehierarchies.classic.no_cache import NoCache
from gem5.components.processors.simple_processor import SimpleProcessor
from gem5.simulate.simulator import Simulator

# This check ensures the gem5 binary is compiled to the RISCV ISA target.
# If not, an exception will be thrown.
requires(isa_required=ISA.RISCV)

# In this setup we don't have a cache. `NoCache` can be used for such setups.
cache_hierarchy = NoCache()

# We use a single channel DDR3_1600 memory system
memory = SingleChannelDDR3_1600(size="32MB")

# We use a simple Timing processor with one core.
processor = SimpleProcessor(cpu_type=CPUTypes.TIMING, isa=ISA.RISCV,
                            num_cores=1)

# The gem5 library simble board which can be used to run simple SE-mode
# simulations.
board = SimpleBoard(
    clk_freq="3GHz",
    processor=processor,
    memory=memory,
    cache_hierarchy=cache_hierarchy,
)

# Here we set the workload. In this case we want to run a simple "Hello World!"
# program compiled to the RISCV ISA. The `Resource` class will automatically
# download the binary from the gem5 Resources cloud bucket if it's not already
# present.
board.set_se_binary_workload(
    # The `Resource` class reads the `resources.json` file from the gem5
    # resources repository:
    # https://gem5.googlesource.com/public/gem5-resource.
    # Any resource specified in this file will be automatically retrieved.
    # At the time of writing, this file is a WIP and does not contain all
    # resources. Jira ticket: https://gem5.atlassian.net/browse/GEM5-1096
    Resource("riscv-hello")
)

# Lastly we run the simulation.
max_ticks = 10**6
simulator = Simulator(board=board, full_system=False)
simulator.run(max_ticks = max_ticks)

print(
    "Exiting @ tick {} because {}.".format(
        simulator.get_current_tick(),
        simulator.get_last_exit_event_cause(),
    )
)

checkpoint_path = "riscv-hello-checkpoint/"
print("Taking a checkpoint at", checkpoint_path)
simulator.save_checkpoint(checkpoint_path)
print("Done taking a checkpoint")