Question

对于一个项目，我在RS485串行线路上连接了4个modbus设备。设备工作正常，现在我正在编写一个控制器，我对pymodbus的性能非常不满意。

我找到了这个帖子Python modbus library，在我看来可能有更好的python modbus库。 pymodbus易于使用，我希望在可能的情况下继续使用它。

但是我发现任何读/写例程返回的时间都等于超时。这对我来说似乎不对，所以我写了一个快速测试：

from pymodbus.client.sync import  ModbusSerialClient
import time

for t in xrange(1, 11):
    client = ModbusSerialClient("rtu", port="/dev/ttyUSB0", baudrate=9600, timeout=t)

    start = time.time()
    data = client.read_holding_registers(0x9000, count=7, unit=2)
    stop = time.time()

    if data:
        succ = "was successful"
    else:
        succ = "failed"

    print "timeout: %ss, read %s, time spent reading: %fs" % (t, succ, stop-start)

这是我得到的输出

timeout: 1s, read was successful, time spent reading: 1.039731s
timeout: 2s, read was successful, time spent reading: 2.038965s
timeout: 3s, read was successful, time spent reading: 3.041441s
timeout: 4s, read was successful, time spent reading: 4.040762s
timeout: 5s, read was successful, time spent reading: 5.043523s
timeout: 6s, read was successful, time spent reading: 6.040139s
timeout: 7s, read was successful, time spent reading: 7.042159s
timeout: 8s, read was successful, time spent reading: 8.045216s
timeout: 9s, read was successful, time spent reading: 9.047682s
timeout: 10s, read was successful, time spent reading: 10.048799s

我已经使用不同的RS845 USB转换器对其进行了测试，我总能得到类似的结果。

任何其他人都能证实这一点吗？或者我错过了一些没有记录的论点会增加ModbusSerialClient的表现？

Answer 1

我可以确认 - 即使收到来自奴隶的响应（在我的情况下为14ms），pymodbus总是等待超时（1-3秒）。所以我用minimalmodbus测试并立即收到响应。在我的情况下，当我用循环测试时，每秒最多35次。

编辑：我找到了原因 - 使用RTU协议时，pymodbus等待超过1000个字节或超时。他们需要计算预期的字节，并且他们有一个修复，但这还没有在主分支（AFAIK）。查看这篇文章https://github.com/bashwork/pymodbus/issues/76所以，如果你真的需要使用pymodbus，你可以尝试补丁。

“ModbusSerialClient”的性能不佳，与超时一样快

1 个答案: