On Wed, Aug 21, 2013 at 10:36:18AM -0700, Simon Gornall wrote: > Hi there, > > I'm in the process of designing a VME=>USB interface, and I wanted to > use the FT232H, but according to FTDI, the throughput on Linux is only > ~9MBytes/sec using current kernels. In the past, it was ~40MBytes/sec. > Sadly my Arm board is delivered running Linux 3.4.29 Why did it drop? What caused the regression? How was this measured? > I don't really want to go back to the "olden days" of kernel 2.6.27-57 > - I'm not even sure it's possible on my embedded ARM board, so I was > wondering if anyone knew the reasons for such a drastic bandwidth > reduction. If it's something I can live with in my embedded situation, > I'd prefer to revert the change and lose whatever functionality was > gained by slashing the bandwidth by 4. > > Basically I need to be able to put 20 MBytes/sec through the USB port. > The FT232H parts are very attractive because they offer a simple > FIFO-style interface and one doesn't have to implement an entire USB > stack, which is much harder when you don't have a CPU ... > > Cheers > Simon. > > Mail from FTDI: > ---8<---8<---8<--- C u t h e r e ---8<---8<---8<--- > > Simon: > > You could use Sync FIFO mode, but I’m afraid there is another “gotcha” > to be aware of - with newer Linux kernels (>2.6.28-3), Sync FIFO > throughput is limited to 9 MByte/sec > > With the older kernels (2.6.27-57 and older) Sync FIFO will run at 40 > MByte/sec. Since you are using ARM Linux, there is a good chance you > have an older kernel. I have no idea what this is referring to at all. Is that just due to a driver change in the ftdi_sio driver, or something else? confused, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
