On Mon, 14 Feb 2005, Nemanja Popov wrote: > > > Now I understand. You say that the SRAM address space is made available > > to the pxa user through your FPGA driver. Can you change that driver to > > make it export the SDRAM contents as a block device file (call it > > /dev/fpga-sdram)? If you can do that, then g-file-storage will be able to > > use the file as the backing storage. > > I'm not shure about that. I'm not that familiar with block device drivers. > If someone have some example I'll appreciatte it. This idea looks like the > most elegant.
I'm not very familiar with them either. The forthcoming book "Linux Device Drivers (third edition)" will undoubtedly have some good examples. > > Another alternative is for you to modify the file_storage.c source code, > > to make it use the SDRAM directly as backing storage instead of going > > through the VFS as it does now. This might be an easier change. It would > > also run faster, since it would avoid the filesystem layer and would have > > fewer data copies. But the speed difference might not be noticeable > > because you are probably limited by the speed of the USB connection rather > > than the speed of data access. > > I don't understand how to cheat host, to see all files and its sizes on > SDRAM. Don't I need a filesystem to provide such info. If you want the host to see a filesystem, then yes, you would need to have a filesystem stored in the SDRAM. But if you don't mind making the user programs access the contents of SDRAM directly then you don't need a filesystem. Notice that you would face this same problem if you adopt the suggestion above, using /dev/fpga-sdram as a backing file. Either way, the host won't see a filesystem unless one is stored in the SDRAM contents. > I guess (when using backing file) host sees all files and their's sizes > stored on backing file, and when tries to copy some file from backing > storage to some folder, it sends READ request through USB connection to the > target. That READ request includes size in bytes which needs to be read. To > be clear, how to tell host what is the size of the file we want to copy. I > don't know much about fs, partition tables and stuff If you access the SDRAM contents directly, you don't need to know that stuff. > Also, is using g_ether good idea for this purpose? What transfer rate I can > get when using USB2.0 NET2272 device (not on board yet) in both variants, > with g_file_storage or g_ether. I don't know, but I imagine the transfer rate is limited more by the speed of the USB connection than by the protocol you use. Alan Stern ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://ads.osdn.com/?ad_id=6595&alloc_id=14396&op=click _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
