Document alternates 3 and 4.

diff --git a/bmusb.cpp b/bmusb.cpp
index a176f936a79d38f05c509e3c66019b98f7ac2b3b..16da5f01e467409188f4cb3ab92335631802d401 100644 (file)
--- a/bmusb.cpp
+++ b/bmusb.cpp
@@ -682,6 +682,9 @@ void BMUSBCapture::configure_card()
        // Alternate setting 1 is output, alternate setting 2 is input.
        // Card is reset when switching alternates, so the driver uses
        // this “double switch” when it wants to reset.
+       //
+       // There's also alternate settings 3 and 4, which seem to be
+       // like 1 and 2 except they advertise less bandwidth needed.
        rc = libusb_set_interface_alt_setting(devh, /*interface=*/0, /*alternate_setting=*/1);
        if (rc < 0) {
                fprintf(stderr, "Error setting alternate 1: %s\n", libusb_error_name(rc));