// Copyright Keysight Technologies 2012-2019
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// This Source Code Form is subject to the terms of the Mozilla Public
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// License, v. 2.0. If a copy of the MPL was not distributed with this
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// file, you can obtain one at http://mozilla.org/MPL/2.0/.
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using System;
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using System.Linq;
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using System.Threading;
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using System.Text;
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namespace OpenTap
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{
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/// <summary>
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/// Implements device address discovery for VISA Keysight instruments and searches for device aliases.
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/// </summary>
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class VisaDeviceDiscovery : IDeviceDiscovery
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{
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static bool IsVisaDiscoveryDisabled()
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{
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var env = Environment.GetEnvironmentVariable("OPENTAP_NO_VISA_DISCOVERY");
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if (env == null)
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return false;
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return string.Equals(env, "True",StringComparison.OrdinalIgnoreCase) || string.Equals(env, "1");
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}
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static readonly bool isDisabled = IsVisaDiscoveryDisabled();
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private static string[] GetDeviceAddresses()
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{
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var rm = GetResourceManager();
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if (rm == Visa.VI_NULL) return new string[0];
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int search, cnt;
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StringBuilder sb = new StringBuilder(1024);
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if (Visa.viFindRsrc(rm, "?*", out search, out cnt, sb) >= Visa.VI_SUCCESS)
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{
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string[] res = new string[cnt];
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if (cnt > 0)
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res[0] = sb.ToString();
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int i = 1;
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while ((cnt-- > 0) && (Visa.viFindNext(search, sb) == Visa.VI_SUCCESS))
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{
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res[i++] = sb.ToString();
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}
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if (i < res.Length)
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Array.Resize(ref res, i);
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Visa.viClose(search);
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return res;
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}
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return new string[0];
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}
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static bool getAliasesBroken = false;
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static string[] getAliases(int rm, string address)
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{
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if (getAliasesBroken) return Array.Empty<string>();
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using (var semaphore = new Semaphore(0, 1))
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{
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string[] result = Array.Empty<string>();
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TapThread.Start(() =>
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{
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var aliases = new StringBuilder(1024);
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short intfType = 0;
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short intfNum = 0;
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if (Visa.viParseRsrcEx(rm, address, ref intfType, ref intfNum, null, null, aliases) ==
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Visa.VI_SUCCESS)
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{
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if (aliases.Length != 0)
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result = new[] {aliases.ToString()};
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}
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semaphore.Release();
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});
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if (!semaphore.WaitOne(5000))
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{
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getAliasesBroken = true;
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log.Warning("VISA timed out when trying to get aliases. Skipping this from now on.");
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}
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return result;
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}
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}
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/// <summary> Ensures updating device addresses is run from the same thread.</summary>
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static WorkQueue detectAddressQueue = new WorkQueue(WorkQueue.Options.None, nameof(VisaDeviceDiscovery));
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static string[] deviceAddresses = null; // not null after first detect.
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static void updateDeviceAddresses()
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{
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try
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{
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var baseAddresses = GetDeviceAddresses();
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// Now expand aliases
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var rm = GetResourceManager();
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if (rm == Visa.VI_NULL)
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{
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deviceAddresses = baseAddresses;
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}
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else
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{
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deviceAddresses = baseAddresses.SelectMany(addr => getAliases(rm, addr)).Concat(baseAddresses).ToArray();
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}
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}
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catch
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{
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deviceAddresses = Array.Empty<string>();
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}
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}
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static TraceSource log = Log.CreateSource(nameof(VisaDeviceDiscovery));
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public string[] DetectDeviceAddresses(DeviceAddressAttribute AddressType)
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{
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if (isDisabled) return Array.Empty<string>();
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using (var wait = new ManualResetEvent(false))
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{
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bool doUpdate = detectAddressQueue.QueueSize == 0;
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detectAddressQueue.EnqueueWork(() =>
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{
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if (doUpdate)
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updateDeviceAddresses();
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if (!wait.SafeWaitHandle.IsClosed)
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wait.Set();
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});
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if (!wait.WaitOne(deviceAddresses == null ? 2000 : 100))
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{
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// updateDeviceAddresses can hang forever in case of an error in the VISA installation.
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// in this case wait for a bit and return no result. Consequent times wait a very short time.
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Utils.ErrorOnce(log, log, "Detecting device addresses took longer than expected. This might be caused by a broken VISA installation.");
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}
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return deviceAddresses ?? Array.Empty<string>();
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}
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}
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/// <summary> Returns true if DeviceAddress is a VISA address. </summary>
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/// <param name="DeviceAddress">. </param>
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/// <returns> </returns>
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public bool CanDetect(DeviceAddressAttribute DeviceAddress)
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{
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if (isDisabled) return false;
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return (DeviceAddress is VisaAddressAttribute);
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}
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static int visa_resource;
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static bool visa_tried_load;
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// Required by .NET to catch AccessViolationException.
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[System.Runtime.ExceptionServices.HandleProcessCorruptedStateExceptions]
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internal static int GetResourceManager()
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{
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try
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{
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if (visa_resource == Visa.VI_NULL && !visa_tried_load)
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RaiseError2(Visa.viOpenDefaultRM(out visa_resource));
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}
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catch (Exception)
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{
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visa_tried_load = true;
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}
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return visa_resource;
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}
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private static void RaiseError2(int error)
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{
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if (error < 0)
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throw new Exception("Visa failed with error " + error);
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}
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}
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}
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