正在尝试从没有读取终止的设备读取可变长度数据(_T)

Question

我可以使用miniterm.py从信号发生器读写信号。流中没有read_termination字符(根据设备制造商的手册(。我附上了来自miniterm的调试输出，以显示一些事务。让pyvisa在没有终止的情况下读取任意长度的返回字符串，我缺少什么吗？

------------------------最小输出-----------------------

设置：/dev/ttyUSB0 9600,8，N，1RTS:活动DTR:活动BREAK:不活动CTS:非活动DSR:非活动RI:非活动CD:非活动软件流控制：不活动硬件流控制：不活动串行输入编码：UTF-8串行输出编码：UTF-8EOL:LF过滤器：调试默认的直接

[TX:'R'][TX:'M'][TX:'W'][TX:%n'][RX:'3']3[RX:'6']6[TX:'R'][TX:'F'][TX：'W'][TC:'\n'][RX:'0']0[TX:'R'][TX：'M'][TK:'A'][TX:0'][RX:'2']2[RX:0']0[RX:'0']0[TC:'R']：'A'][TX:'\n'][RX:'1']1[RX:'0']0[RX:'0']0[RR:'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"错误告终。

提前谢谢。

Robin

Answer 1

下面的read_data((函数在一定程度上解决了这个问题。现在要弄清楚为什么背靠背写入失败，除非两次写入之间不使用大约0.2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为您提供缓冲区和内的字节数

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

之后，您可以调用answer.decode()来获取设备返回给您的ASCII字符串。下面是我为简化与设备的通信而编写的Python类的一个较长示例：

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]
))