Add support for specifying which FluxEngine you want to use with the --devices

parameter.

lib/fluxsink/hardwarefluxsink.cc

@@ -4,7 +4,9 @@
 #include "usb/usb.h"
 #include "fluxsink/fluxsink.h"
 
-FlagGroup hardwareFluxSinkFlags;
+FlagGroup hardwareFluxSinkFlags = {
+	&usbFlags,
+};
 
 static bool high_density = false;
 

lib/fluxsource/hardwarefluxsource.cc

@@ -5,7 +5,9 @@
 #include "fluxsource/fluxsource.h"
 #include "fmt/format.h"
 
-FlagGroup hardwareFluxSourceFlags;
+FlagGroup hardwareFluxSourceFlags = {
+	&usbFlags
+};
 
 static DoubleFlag revolutions(
     { "--revolutions" },

lib/usb/fluxengineusb.cc

@@ -54,16 +54,11 @@ private:
 	}
 
 public:
-	FluxEngineUsb()
+	FluxEngineUsb(libusb_device_handle* device)
 	{
-		int i = libusb_init(NULL);
-		if (i < 0)
-			Error() << "could not start libusb: " << usberror(i);
-
-		_device = libusb_open_device_with_vid_pid(NULL, FLUXENGINE_VID, FLUXENGINE_PID);
-		if (!_device)
-			Error() << "cannot find the FluxEngine (is it plugged in?)";
+		_device = device;
 
+		int i;
 		int cfg = -1;
 		libusb_get_configuration(_device, &cfg);
 		if (cfg != 1)
@@ -77,7 +72,7 @@ public:
 		if (i < 0)
 			Error() << "could not claim interface: " << usberror(i);
 
-		int version = usbGetVersion();
+		int version = getVersion();
 		if (version != FLUXENGINE_VERSION)
 			Error() << "your FluxEngine firmware is at version " << version
 					<< " but the client is for version " << FLUXENGINE_VERSION
@@ -324,8 +319,8 @@ public:
 	}
 };
 
-USB* createFluxengineUsb()
+USB* createFluxengineUsb(libusb_device_handle* device)
 {
-	return new FluxEngineUsb();
+	return new FluxEngineUsb(device);
 }
 

lib/usb/usb.cc

@@ -1,4 +1,5 @@
 #include "globals.h"
+#include "flags.h"
 #include "usb.h"
 #include "protocol.h"
 #include "fluxmap.h"
@@ -6,8 +7,28 @@
 #include <libusb.h>
 #include "fmt/format.h"
 
+FlagGroup usbFlags;
+
+static StringFlag device(
+    { "--device" },
+    "serial number of hardware device to use",
+	"");
+
 static USB* usb = NULL;
 
+enum
+{
+	DEV_FLUXENGINE,
+};
+
+struct CandidateDevice
+{
+	libusb_device* device;
+	libusb_device_descriptor desc;
+	int type;
+	std::string serial;
+};
+
 USB::~USB()
 {}
 
@@ -16,10 +37,99 @@ std::string USB::usberror(int i)
     return libusb_strerror((libusb_error) i);
 }
 
+static std::map<std::string, std::unique_ptr<CandidateDevice>> get_candidates(libusb_device** devices, int numdevices)
+{
+	std::map<std::string, std::unique_ptr<CandidateDevice>> candidates;
+	for (int i=0; i<numdevices; i++)
+	{
+		std::unique_ptr<CandidateDevice> candidate(new CandidateDevice());
+		candidate->device = devices[i];
+		(void) libusb_get_device_descriptor(devices[i], &candidate->desc);
+
+		if ((candidate->desc.idVendor == FLUXENGINE_VID) && (candidate->desc.idProduct == FLUXENGINE_PID))
+		{
+			candidate->type = DEV_FLUXENGINE;
+			candidate->serial = "";
+
+			libusb_device_handle* handle;
+			if (libusb_open(candidate->device, &handle) == 0)
+			{
+				unsigned char buffer[64];
+				libusb_get_string_descriptor_ascii(handle,
+					candidate->desc.iSerialNumber, buffer, sizeof(buffer));
+				candidate->serial = (const char*) buffer;
+				libusb_close(handle);
+			}
+
+			candidates[candidate->serial] = std::move(candidate);
+		}
+	}
+
+	return candidates;
+}
+
+static void open_device(CandidateDevice& candidate)
+{
+	libusb_device_handle* handle;
+	int i = libusb_open(candidate.device, &handle);
+	if (i < 0)
+		Error() << "cannot open USB device: " << libusb_strerror((libusb_error) i);
+	
+	usb = createFluxengineUsb(handle);
+}
+
+static CandidateDevice& select_candidate(const std::map<std::string, std::unique_ptr<CandidateDevice>>& devices)
+{
+	if (devices.size() == 0)
+		Error() << "no USB devices found (is one plugged in? Do you have permission to access USB devices?)";
+
+	if (device.get() == "")
+	{
+		if (devices.size() == 1)
+			return *devices.begin()->second;
+
+		std::cout << "More than one USB device detected. Use --device to specify which one to use:\n";
+		for (auto& i : devices)
+		{
+			std::cout << "  " << i.first << ": ";
+			switch (i.second->type)
+			{
+				case DEV_FLUXENGINE: std::cout << "FluxEngine";
+			}
+			std::cout << '\n';
+		}
+		Error() << "specify USB device";
+	}
+	else
+	{
+		const auto& i = devices.find(device);
+		if (i != devices.end())
+			return *i->second;
+
+		Error() << "device with serial number '" << device.get() << "' not found";
+	}
+}
+
 USB& getUsb()
 {
 	if (!usb)
-		usb = createFluxengineUsb();
+	{
+		int i = libusb_init(NULL);
+		if (i < 0)
+			Error() << "could not start libusb: " << libusb_strerror((libusb_error) i);
+
+		libusb_device** devices;
+		int numdevices = libusb_get_device_list(NULL, &devices);
+		if (numdevices < 0)
+			Error() << "could not enumerate USB bus: " << libusb_strerror((libusb_error) numdevices);
+
+		auto candidates = get_candidates(devices, numdevices);
+		auto candidate = select_candidate(candidates);
+		open_device(candidate);
+
+		libusb_free_device_list(devices, true);
+
+	}
 
 	return *usb;
 }

lib/usb/usb.h

@@ -2,6 +2,7 @@
 #define USB_H
 
 #include "bytes.h"
+#include "flags.h"
 
 class Fluxmap;
 class libusb_device_handle;
@@ -29,9 +30,10 @@ protected:
 	libusb_device_handle* _device;
 };
 
+extern FlagGroup usbFlags;
 extern USB& getUsb();
 
-extern USB* createFluxengineUsb();
+extern USB* createFluxengineUsb(libusb_device_handle* device);
 
 static inline int usbGetVersion()     { return getUsb().getVersion(); }
 static inline void usbRecalibrate()   { getUsb().recalibrate(); }

src/fe-rpm.cc

@@ -4,7 +4,9 @@
 #include "dataspec.h"
 #include "protocol.h"
 
-static FlagGroup flags;
+static FlagGroup flags = {
+	&usbFlags,
+};
 
 static DataSpecFlag source(
     { "--source", "-s" },

src/fe-seek.cc

@@ -3,7 +3,9 @@
 #include "usb/usb.h"
 #include "protocol.h"
 
-static FlagGroup flags;
+static FlagGroup flags = {
+	&usbFlags,
+};
 
 static IntFlag drive(
     { "--drive", "-d" },

src/fe-testbandwidth.cc

@@ -2,7 +2,9 @@
 #include "flags.h"
 #include "usb/usb.h"
 
-static FlagGroup flags;
+static FlagGroup flags = {
+	&usbFlags,
+};
 
 int mainTestBandwidth(int argc, const char* argv[])
 {

src/fe-testvoltages.cc

@@ -4,7 +4,9 @@
 #include "protocol.h"
 #include <fmt/format.h>
 
-static FlagGroup flags;
+static FlagGroup flags = {
+	&usbFlags,
+};
 
 static std::string display_voltages(struct voltages& v)
 {