Simon Gornall <simon.gornall@...> writes: > > 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 > > 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. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-usb" in > the body of a message to majordomo@... > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Hi Simon, we are having exactly the same problem you are, Sync FIFO throughput on the order of 8 MBytes/sec, when we really need at least 20 to meet other system requirements. My current development platform is a fairly elderly PC based on an old AMD XP2700 CPU, using Ubuntu 12.04 at the moment. I received the same information from FTDI as you did, that the older Linux kernels did not show this problem. I located the Ubuntu release incorporating the last kernel known to work (8.10), installed it on a different hard drive, and running the same binary for my code was suddenly seeing transfers rates around 30 MBytes/sec. I really don't want to use this as our fix for production, I am pretty sure that this Ubuntu distro is no longer supported, dating from 2008. I wonder if you have had any success getting your speed up, and if so how did you do it? Thanks, Warren Taylor -- 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
