我必须控制带有串行接口(interface)的 modbus 设备。我没有使用 modbus 的经验。但我的简短研究揭示了几个 modbus 库
有什么优点/缺点,还有更好的选择吗?
最佳答案
大约在同一时间,我遇到了同样的问题 - 为 python modbus master 实现选择哪个库,但在我的情况下是串行通信(modbus RTU),所以我的观察只对 modbus RTU 有效。
在我的考试中,我并没有过多关注文档,但是对于 modbus-tk 最容易找到串行 RTU 主站的示例,但是仍然在源代码中,而不是在 wiki 等上。
长话短说:
最小Modbus:
pymodbus:
显着特点:依赖于串行流( post by the author ),串行超时必须动态设置,否则性能会很低(必须调整串行超时以获得尽可能长的响应)
modbus-tk:
显着特点:探测串行缓冲区数据,快速组装和返回响应。
6 个多月以来,由于最佳性能/CPU 负载率,我一直在使用 pymodbus,但在更高的请求率下,不可靠的响应成为一个严重问题,最终我转向了更快的嵌入式系统,并添加了对 modbus-tk 的支持,这对我来说效果最好。
对于那些对细节感兴趣的人
我的目标是实现最短的响应时间。
设置:
用例场景:
典型的长期(数周)表现:
基准
代码:
import time
import traceback
import serial
import modbus_tk.defines as tkCst
import modbus_tk.modbus_rtu as tkRtu
import minimalmodbus as mmRtu
from pymodbus.client.sync import ModbusSerialClient as pyRtu
slavesArr = [2]
iterSp = 100
regsSp = 10
portNbr = 21
portName = 'com22'
baudrate = 153600
timeoutSp=0.018 + regsSp*0
print "timeout: %s [s]" % timeoutSp
mmc=mmRtu.Instrument(portName, 2) # port name, slave address
mmc.serial.baudrate=baudrate
mmc.serial.timeout=timeoutSp
tb = None
errCnt = 0
startTs = time.time()
for i in range(iterSp):
for slaveId in slavesArr:
mmc.address = slaveId
try:
mmc.read_registers(0,regsSp)
except:
tb = traceback.format_exc()
errCnt += 1
stopTs = time.time()
timeDiff = stopTs - startTs
mmc.serial.close()
print mmc.serial
print "mimalmodbus:\ttime to read %s x %s (x %s regs): %.3f [s] / %.3f [s/req]" % (len(slavesArr),iterSp, regsSp, timeDiff, timeDiff/iterSp)
if errCnt >0:
print " !mimalmodbus:\terrCnt: %s; last tb: %s" % (errCnt, tb)
pymc = pyRtu(method='rtu', port=portNbr, baudrate=baudrate, timeout=timeoutSp)
errCnt = 0
startTs = time.time()
for i in range(iterSp):
for slaveId in slavesArr:
try:
pymc.read_holding_registers(0,regsSp,unit=slaveId)
except:
errCnt += 1
tb = traceback.format_exc()
stopTs = time.time()
timeDiff = stopTs - startTs
print "pymodbus:\ttime to read %s x %s (x %s regs): %.3f [s] / %.3f [s/req]" % (len(slavesArr),iterSp, regsSp, timeDiff, timeDiff/iterSp)
if errCnt >0:
print " !pymodbus:\terrCnt: %s; last tb: %s" % (errCnt, tb)
pymc.close()
tkmc = tkRtu.RtuMaster(serial.Serial(port=portNbr, baudrate=baudrate))
tkmc.set_timeout(timeoutSp)
errCnt = 0
startTs = time.time()
for i in range(iterSp):
for slaveId in slavesArr:
try:
tkmc.execute(slaveId, tkCst.READ_HOLDING_REGISTERS, 0,regsSp)
except:
errCnt += 1
tb = traceback.format_exc()
stopTs = time.time()
timeDiff = stopTs - startTs
print "modbus-tk:\ttime to read %s x %s (x %s regs): %.3f [s] / %.3f [s/req]" % (len(slavesArr),iterSp, regsSp, timeDiff, timeDiff/iterSp)
if errCnt >0:
print " !modbus-tk:\terrCnt: %s; last tb: %s" % (errCnt, tb)
tkmc.close()
结果:platform:
P8700 @2.53GHz
WinXP sp3 32bit
Python 2.7.1
FTDI FT232R series 1220-0
FTDI driver 2.08.26 (watch out for possible issues with 2.08.30 version on Windows)
pymodbus version 1.2.0
MinimalModbus version 0.4
modbus-tk version 0.4.2
读取 100 x 64 寄存器:不省电
timeout: 0.05 [s]
Serial<id=0xd57330, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.05, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 64 regs): 9.135 [s] / 0.091 [s/req]
pymodbus: time to read 1 x 100 (x 64 regs): 6.151 [s] / 0.062 [s/req]
modbus-tk: time to read 1 x 100 (x 64 regs): 2.280 [s] / 0.023 [s/req]
timeout: 0.03 [s]
Serial<id=0xd57330, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.03, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 64 regs): 7.292 [s] / 0.073 [s/req]
pymodbus: time to read 1 x 100 (x 64 regs): 3.170 [s] / 0.032 [s/req]
modbus-tk: time to read 1 x 100 (x 64 regs): 2.342 [s] / 0.023 [s/req]
timeout: 0.018 [s]
Serial<id=0xd57330, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.018, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 64 regs): 4.481 - 7.198 [s] / 0.045 - 0.072 [s/req]
pymodbus: time to read 1 x 100 (x 64 regs): 3.045 [s] / 0.030 [s/req]
modbus-tk: time to read 1 x 100 (x 64 regs): 2.342 [s] / 0.023 [s/req]
最大节能timeout: 0.05 [s]
Serial<id=0xd57330, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.05, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 64 regs): 10.289 [s] / 0.103 [s/req]
pymodbus: time to read 1 x 100 (x 64 regs): 6.074 [s] / 0.061 [s/req]
modbus-tk: time to read 1 x 100 (x 64 regs): 2.358 [s] / 0.024 [s/req]
timeout: 0.03 [s]
Serial<id=0xd57330, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.03, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 64 regs): 8.166 [s] / 0.082 [s/req]
pymodbus: time to read 1 x 100 (x 64 regs): 4.138 [s] / 0.041 [s/req]
modbus-tk: time to read 1 x 100 (x 64 regs): 2.327 [s] / 0.023 [s/req]
timeout: 0.018 [s]
Serial<id=0xd57330, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.018, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 64 regs): 7.776 [s] / 0.078 [s/req]
pymodbus: time to read 1 x 100 (x 64 regs): 3.169 [s] / 0.032 [s/req]
modbus-tk: time to read 1 x 100 (x 64 regs): 2.342 [s] / 0.023 [s/req]
读取 100 x 10 寄存器:不省电
timeout: 0.05 [s]
Serial<id=0xd56350, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.05, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 10 regs): 6.246 [s] / 0.062 [s/req]
pymodbus: time to read 1 x 100 (x 10 regs): 6.199 [s] / 0.062 [s/req]
modbus-tk: time to read 1 x 100 (x 10 regs): 1.577 [s] / 0.016 [s/req]
timeout: 0.03 [s]
Serial<id=0xd56350, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.03, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 10 regs): 3.088 [s] / 0.031 [s/req]
pymodbus: time to read 1 x 100 (x 10 regs): 3.143 [s] / 0.031 [s/req]
modbus-tk: time to read 1 x 100 (x 10 regs): 1.533 [s] / 0.015 [s/req]
timeout: 0.018 [s]
Serial<id=0xd56350, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.018, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 10 regs): 3.066 [s] / 0.031 [s/req]
pymodbus: time to read 1 x 100 (x 10 regs): 3.006 [s] / 0.030 [s/req]
modbus-tk: time to read 1 x 100 (x 10 regs): 1.533 [s] / 0.015 [s/req]
最大节能timeout: 0.05 [s]
Serial<id=0xd56350, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.05, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 10 regs): 6.386 [s] / 0.064 [s/req]
pymodbus: time to read 1 x 100 (x 10 regs): 5.934 [s] / 0.059 [s/req]
modbus-tk: time to read 1 x 100 (x 10 regs): 1.499 [s] / 0.015 [s/req]
timeout: 0.03 [s]
Serial<id=0xd56350, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.03, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 10 regs): 3.139 [s] / 0.031 [s/req]
pymodbus: time to read 1 x 100 (x 10 regs): 3.170 [s] / 0.032 [s/req]
modbus-tk: time to read 1 x 100 (x 10 regs): 1.562 [s] / 0.016 [s/req]
timeout: 0.018 [s]
Serial<id=0xd56350, open=False>(port='com22', baudrate=153600, bytesize=8, parity='N', stopbits=1, timeout=0.018, xonxoff=False, rtscts=False, dsrdtr=False)
mimalmodbus: time to read 1 x 100 (x 10 regs): 3.123 [s] / 0.031 [s/req]
pymodbus: time to read 1 x 100 (x 10 regs): 3.060 [s] / 0.031 [s/req]
modbus-tk: time to read 1 x 100 (x 10 regs): 1.561 [s] / 0.016 [s/req]
实际应用:modbus-rpc 桥的负载示例(~3% 是由 RPC 服务器部分引起的)
编辑: modbus-tk 库可以轻松改进以减少 CPU 使用率。
在原始版本中,发送请求并通过 T3.5 sleep 后,主机一次一个字节地组装响应。分析证明大部分时间都花在了串行端口访问上。这可以通过尝试从串行缓冲区读取预期长度的数据来改进。根据 pySerial documentation如果设置了超时,它应该是安全的(当响应丢失或太短时不会挂断):
read(size=1)
Parameters: size – Number of bytes to read.
Returns: Bytes read from the port.
Read size bytes from the serial port. If a timeout is set it may return less characters as
requested. With no timeout it will block until the requested number of bytes is read.
按以下方式修改“modbus_rtu.py”后:def _recv(self, expected_length=-1):
"""Receive the response from the slave"""
response = ""
read_bytes = "dummy"
iterCnt = 0
while read_bytes:
if iterCnt == 0:
read_bytes = self._serial.read(expected_length) # reduces CPU load for longer frames; serial port timeout is used anyway
else:
read_bytes = self._serial.read(1)
response += read_bytes
if len(response) >= expected_length >= 0:
#if the expected number of byte is received consider that the response is done
#improve performance by avoiding end-of-response detection by timeout
break
iterCnt += 1
在 modbus-tk 修改后,实际应用程序中的 CPU 负载大幅下降,而没有显着的性能损失(仍然比 pymodbus 好):更新 modbus-rpc 桥的负载示例(约 3% 是由 RPC 服务器部分引起的)
关于Python modbus 库,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17081442/