Make sure that places which use usbSeek() honour --40-track.

lib/flaggroups/fluxsourcesink.cc

@@ -5,7 +5,7 @@
 FlagGroup fluxSourceSinkFlags;
 
 SettableFlag fluxSourceSinkFortyTrack(
-	{ "--40-track" },
+	{ "--40-track", "-4" },
 	"indicates a 40 track drive");
 
 SettableFlag fluxSourceSinkHighDensity(

src/fe-analysedriveresponse.cc

@@ -7,11 +7,13 @@
 #include "writer.h"
 #include "protocol.h"
 #include "fmt/format.h"
+#include "flaggroups/fluxsourcesink.h"
 #include "dep/agg/include/agg2d.h"
 #include "dep/stb/stb_image_write.h"
 #include <fstream>
 
 static FlagGroup flags = {
+	&fluxSourceSinkFlags,
 	&usbFlags,
 };
 
@@ -186,8 +188,15 @@ int mainAnalyseDriveResponse(int argc, const char* argv[])
 	if (spec.locations.size() != 1)
 		Error() << "the destination dataspec must contain exactly one track (two sides count as two tracks)";
 
-    usbSetDrive(spec.drive, false, F_INDEX_REAL);
-	usbSeek(spec.locations[0].track);
+    usbSetDrive(spec.drive, fluxSourceSinkHighDensity, F_INDEX_REAL);
+	int track = spec.locations[0].track;
+	if (fluxSourceSinkFortyTrack)
+	{
+		if (track & 1)
+			Error() << "you can only seek to even tracks on a 40-track disk";
+		track /= 2;
+	}
+	usbSeek(track);
 
 	std::cout << "Measuring rotational speed...\n";
     nanoseconds_t period = usbGetRotationalPeriod(0);

src/fe-seek.cc

@@ -1,9 +1,11 @@
 #include "globals.h"
 #include "flags.h"
 #include "usb/usb.h"
+#include "flaggroups/fluxsourcesink.h"
 #include "protocol.h"
 
 static FlagGroup flags = {
+	&fluxSourceSinkFlags,
 	&usbFlags,
 };
 
@@ -22,6 +24,13 @@ int mainSeek(int argc, const char* argv[])
     flags.parseFlags(argc, argv);
 
     usbSetDrive(drive, false, F_INDEX_REAL);
-    usbSeek(track);
+	if (fluxSourceSinkFortyTrack)
+	{
+		if (track & 1)
+			Error() << "you can only seek to even tracks on a 40-track drive";
+		usbSeek(track / 2);
+	}
+	else
+		usbSeek(track);
     return 0;
 }