In message <[EMAIL PROTECTED]>, Hans Petter Selasky writes: >Ok. So the solution to my problem is to use scatter and gather. I will see >about updating my USB system to do it like that. > >But there is one thing I do not understand yet. When you load a page that >physically resides above 4GB, because a computer has more than 4GB of memory, >how does "bus_dmamap_load()" move that page down below 4GB, so that the >32-bit USB host controllers can reach it?
What should happen is that bus_dma allocates a bounce buffer and performs copies as required from within the bus_dmamap_sync() calls. This is something I haven't been able to verify yet with the USB code though, so there could easily be bugs there. BTW, as far as I know bus_dma is also missing support for multi-segment allocations, so for example if you ask it to allocate 16k in at most 4 segments below the 4GB mark, it will actually attempt a physically contiguous allocation. If this was fixed it could be used by usbd_alloc_buffer() to give directly usable buffers without contiguous allocations. Ian _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
