Add support for persistent USB device memory.

This patch lived out-of-tree for a long time; now that libusb in git
has taken in the functionality needed, we can pull it in, even though
the version define isn't good enough to check the actual functionality.
It can distinguish git from last release, though, and that's the most
important thing.

diff --git a/bmusb.cpp b/bmusb.cpp
index 3aac81e5e34e5de7459585630635eab8a460d25a..ed7a1f5caa42874909bf13804210322ee34942b5 100644 (file)
--- a/bmusb.cpp
+++ b/bmusb.cpp
@@ -1028,7 +1028,7 @@ void BMUSBCapture::configure_card()
        // set up isochronous transfers for audio and video
        for (int e = 3; e <= 4; ++e) {
                //int num_transfers = (e == 3) ? 6 : 6;
-               int num_transfers = 10;
+               int num_transfers = 6;
                for (int i = 0; i < num_transfers; ++i) {
                        size_t buf_size;
                        int num_iso_pack, size;
@@ -1044,8 +1044,23 @@ void BMUSBCapture::configure_card()
                                num_iso_pack = 80;
                                buf_size = num_iso_pack * size;
                        }
-                       assert(size_t(num_iso_pack * size) <= buf_size);
-                       uint8_t *buf = new uint8_t[buf_size];
+                       int num_bytes = num_iso_pack * size;
+                       assert(size_t(num_bytes) <= buf_size);
+#if LIBUSB_API_VERSION >= 0x01000105
+                       uint8_t *buf = libusb_dev_mem_alloc(devh, num_bytes);
+#else
+                       uint8_t *buf = nullptr;
+#endif
+                       if (buf == nullptr) {
+                               fprintf(stderr, "Failed to allocate persistent DMA memory ");
+#if LIBUSB_API_VERSION >= 0x01000105
+                               fprintf(stderr, "(probably too old kernel; use 4.6.0 or newer).\n");
+#else
+                               fprintf(stderr, "(compiled against too old libusb-1.0).\n");
+#endif
+                               fprintf(stderr, "Will go slower, and likely fail due to memory fragmentation after a few hours.\n");
+                               buf = new uint8_t[num_bytes];
+                       }
 
                        xfr = libusb_alloc_transfer(num_iso_pack);
                        if (!xfr) {