python - pyvisa -尝试从没有读取_termination的设备读取可变长度数据

Question

我可以使用miniterm.py对信号发生器进行读写。流中没有read_termination字符(根据设备制造商的手册)。我已经附加了miniterm的调试输出，以显示一些事务。让pyvisa读取任意长度的返回字符串而不终止是否遗漏了什么？

设置: /dev/ttyUSB0 9600,8，N,1 RTS:活动DTR:活动中断:非活动CTS:非活动DSR:非活动RI:非活动CD:非活动软件流程控制:非活动硬件流程控制:非活动串行输入编码: UTF-8串行输出编码: UTF-8 EOL: LF筛选器: debug default direct

TX:'R‘TX:'W’RX:'3‘3 RX:'6’6 TX:'R‘TX:'W’RX:'0‘0 TX:'R’TX:'A‘RX:'2’2 RX:'0‘0 RX:'0’0 TX:'R‘TX:'A’RX:'1‘1 RX:'0’0 RX:'0‘0 RX:'0’0

任何指向正确方向的指针都会有所帮助。这是一种非常奇怪的设备。我尝试过的大多数东西都以“设备正在使用”或“超时”错误结束。

提前谢谢你。

罗宾

Answer 1

下面的read_data()函数在一定程度上解决了这个问题。现在来找出背靠背写入失败的原因，除非在两次写入之间没有使用大约.2秒的time.sleep(x)。

def read_data(cmd):
    data=""
    byte=""
    looper = True
    dds.write(cmd)
    while(looper==True):
       try:
          byte = dds.read_bytes(1)
          data += byte.decode()
       except:
          looper = False
    return(data)

Answer 2

我在测量仪器上也遇到了同样的问题，花了一段时间才找到解决方案：

device.bytes_in_buffer给出了缓冲区内的字节数和

answer = device.read_bytes( device.bytes_in_buffer )返回缓冲区内的字节数。

之后，您可以调用answer.decode()来获取设备返回给您的ASCII字符串。下面是我写的一个Python类的更长的例子，以使与设备的通信变得更容易：

import pyvisa as visa
import logging as log
import time
from typing import Final, Union

class interface:  # provide write(), read(), read_raw(), ask() and ask_raw() function

    _device = None

    def __init__(self, device) -> None:
        self._device = device

    def write(self, command) -> None:
        self._device.write("%s" % ( command))

    def read(self) -> str:
        return self.read_raw().decode()

    def read_raw(self) -> str:
        return self._device.read_bytes( self._device.bytes_in_buffer )

    def ask(self, command) -> str:
        return self.ask_raw(command).decode()

    # flush buffer, this is necessary to prevent from errors because the last SCPI command took to long to be received
    def flush_buffer(self) -> None:
        self._device.flush(visa.constants.VI_READ_BUF)

    def ask_raw(self, command) -> str:
        self.flush_buffer()
        self.write(command)
        time.sleep(0.2) # this is needed for the device to process the SCPI command
        return self.read_raw()

    def boolean_property(
        self,
        scpi_cmd: str,                  # command name of scpi option
        err_description: str,           # generate usefull error messages
        value: Union[bool, None] = None # True or False -> set scpi option to value, None -> get current value of scpi option
    ) -> Union[bool, None]:

        # if parameter value is None -> get current state from scpi option
        if value == None:
            return {
                "ON": True,
                "1": True,
                "OFF": False,
                "0": False
            }[str(
                self.ask("%s?" % (scpi_cmd.upper()))
            ).upper()]   # uppercase conversion is used to prevent issues with unexpected lowercase letters

        # check wether the parameter is a boolean
        if not type(value) == bool:
            return log.error("%s: Cannot assign \"%s\" for %s, must be bool(True) or bool(False)" % (self._device, value, err_description))

        # write the scpi command
        self.write("%s %s" % (
            scpi_cmd,
            {
                True: "ON",
                False: "OFF"
            }[value]
        ))