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98 lines
2.6 KiB
98 lines
2.6 KiB
"""Utilities for reading real time clocks and keeping soft real time constraints."""
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import time
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import ctypes
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import platform
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import subprocess
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import multiprocessing
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import os
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from ctypes.util import find_library
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CLOCK_MONOTONIC_RAW = 4 # see <linux/time.h>
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CLOCK_BOOTTIME = 7
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class timespec(ctypes.Structure):
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_fields_ = [
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('tv_sec', ctypes.c_long),
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('tv_nsec', ctypes.c_long),
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]
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libc_name = find_library('c')
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libc = ctypes.CDLL(libc_name, use_errno=True)
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if hasattr(libc, 'clock_gettime'):
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libc.clock_gettime.argtypes = [ctypes.c_int, ctypes.POINTER(timespec)]
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has_clock_gettime = True
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else:
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has_clock_gettime = False
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def clock_gettime(clk_id):
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if not has_clock_gettime:
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# hack. only for OS X < 10.12
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return time.time()
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t = timespec()
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if libc.clock_gettime(clk_id, ctypes.pointer(t)) != 0:
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errno_ = ctypes.get_errno()
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raise OSError(errno_, os.strerror(errno_))
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return t.tv_sec + t.tv_nsec * 1e-9
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def monotonic_time():
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return clock_gettime(CLOCK_MONOTONIC_RAW)
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def sec_since_boot():
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return clock_gettime(CLOCK_BOOTTIME)
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def set_realtime_priority(level):
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if os.getuid() != 0:
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print("not setting priority, not root")
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return
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if platform.machine() == "x86_64":
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NR_gettid = 186
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elif platform.machine() == "aarch64":
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NR_gettid = 178
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else:
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raise NotImplementedError
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tid = libc.syscall(NR_gettid)
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return subprocess.call(['chrt', '-f', '-p', str(level), str(tid)])
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class Ratekeeper(object):
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def __init__(self, rate, print_delay_threshold=0.):
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"""Rate in Hz for ratekeeping. print_delay_threshold must be nonnegative."""
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self._interval = 1. / rate
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self._next_frame_time = sec_since_boot() + self._interval
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self._print_delay_threshold = print_delay_threshold
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self._frame = 0
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self._remaining = 0
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self._process_name = multiprocessing.current_process().name
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@property
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def frame(self):
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return self._frame
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@property
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def remaining(self):
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return self._remaining
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# Maintain loop rate by calling this at the end of each loop
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def keep_time(self):
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lagged = self.monitor_time()
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if self._remaining > 0:
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time.sleep(self._remaining)
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return lagged
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# this only monitor the cumulative lag, but does not enforce a rate
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def monitor_time(self):
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lagged = False
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remaining = self._next_frame_time - sec_since_boot()
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self._next_frame_time += self._interval
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if remaining < -self._print_delay_threshold:
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print("%s lagging by %.2f ms" % (self._process_name, -remaining * 1000))
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lagged = True
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self._frame += 1
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self._remaining = remaining
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return lagged
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