Add a command to list detectable devices on the command line.

doc/using.md

@@ -58,7 +58,14 @@ If _more_ than one device is plugged in, you need to specify which one to use
 with the `--usb.serial` parameter, which takes the device serial number as a
 parameter.  You can find out the serial numbers by running the command without
 the `--usb.serial` parameter, and if more than one device is attached they will
-be listed. The serial number is also shown whenever a connection is made.
+be listed. The serial number is also shown whenever a connection is made. You
+can list all the detectable devices with:
+
+```
+$ fluxengine test devices
+```
+
+This will show you their serial numbers.
 
 You _can_ work with more than one FluxEngine at the same time, using different
 invocations of the client; but be careful of USB bandwidth. If the devices are

src/build.py

@@ -23,6 +23,7 @@ cxxprogram(
         "./fe-rpm.cc",
         "./fe-seek.cc",
         "./fe-testbandwidth.cc",
+        "./fe-testdevices.cc",
         "./fe-testvoltages.cc",
         "./fe-write.cc",
         "./fileutils.cc",

src/fe-testdevices.cc

@@ -0,0 +1,37 @@
+#include "lib/globals.h"
+#include "lib/flags.h"
+#include "lib/usb/usbfinder.h"
+#include <fmt/format.h>
+
+static FlagGroup flags;
+
+int mainTestDevices(int argc, const char* argv[])
+{
+    flags.parseFlagsWithConfigFiles(argc, argv, {});
+
+    auto candidates = findUsbDevices();
+    switch (candidates.size())
+    {
+        case 0:
+            fmt::print("Detected no devices.\n");
+            break;
+
+        case 1:
+            fmt::print("Detected one device:\n");
+            break;
+
+        default:
+            fmt::print("Detected {} devices:\n", candidates.size());
+    }
+
+    fmt::print("{:15} {:30} {}\n", "Type", "Serial number", "Port (if any)");
+    for (auto& candidate : candidates)
+    {
+        fmt::print("{:15} {:30} {}\n",
+            getDeviceName(candidate->type),
+            candidate->serial,
+            candidate->serialPort);
+    }
+
+    return 0;
+}

src/fluxengine.cc

@@ -23,6 +23,7 @@ extern command_cb mainRm;
 extern command_cb mainRpm;
 extern command_cb mainSeek;
 extern command_cb mainTestBandwidth;
+extern command_cb mainTestDevices;
 extern command_cb mainTestVoltages;
 extern command_cb mainWrite;
 
@@ -69,6 +70,7 @@ static std::vector<Command> analysables =
 static std::vector<Command> testables =
 {
     { "bandwidth",     mainTestBandwidth, "Measures your USB bandwidth.", },
+    { "devices",       mainTestDevices, "Displays all detected devices.", },
     { "voltages",      mainTestVoltages,  "Measures the FDD bus voltages.", },
 };
 // clang-format on