如何在给定时间获取检查点，然后使用gem5 Python API进行恢复？

import m5
from m5.objects import *

system = System()
system.clk_domain = SrcClockDomain()
system.clk_domain.clock = '1GHz'
system.clk_domain.voltage_domain = VoltageDomain()
system.mem_mode = 'timing'
system.mem_ranges = [AddrRange('512MB')]

system.cpu = TimingSimpleCPU()
system.membus = SystemXBar()
system.cpu.icache_port = system.membus.slave
system.cpu.dcache_port = system.membus.slave
system.cpu.createInterruptController()
system.cpu.interrupts[0].pio = system.membus.master
system.cpu.interrupts[0].int_master = system.membus.slave
system.cpu.interrupts[0].int_slave = system.membus.master
system.system_port = system.membus.slave
system.mem_ctrl = DDR3_1600_8x8()
system.mem_ctrl.range = system.mem_ranges[0]
system.mem_ctrl.port = system.membus.master

root = Root(full_system=False, system=system)
m5.instantiate()

m5.simulate(1000000000000)  # 运行1秒钟的仿真，单位为时钟周期

m5.checkpoint('checkpoint')  # 将当前系统状态保存为checkpoint文件

m5.instantiate()  # 重新实例化仿真系统
m5.restore('checkpoint')  # 从checkpoint文件中恢复系统状态
m5.simulate()  # 继续仿真运行