Hi, Dave, All neat ideas, but I'm pretty sure that at least the CASPER implementation of the FPGA side of the EPB bus does not support either burst mode or DMA.
Dave On Oct 16, 2013, at 9:13 AM, David Hawkins wrote: > Hey Ross, > >> Thanks everyone for the input. >> >> I've been trying not to move towards the 10 gb option if possible for >> a couple of reasons but I might have to bite the bullet. >> >> I'm also going to look at another option which is with the mmap kernel I >> have access to the FPGA memory in /dev/roach/mem. I think it should >> be fairly easy to write a custom server that runs on the roach that >> collects the bram data from the mem and then buffers if for sending >> over ethernet via udp. This is probably very similar to what the UDP >> option in tcpborphserver does but I'll be able to control the amount >> of buffering >> >> I guess you could call it a replacement for tcpborphserver that is >> specific for my application. > > Assuming the bottleneck in your datapath is the FPGA<->PowerPC > interface ... > > If the ROACH interface is using /dev/mem for access, then the Power CPU > core is performing the reads; in general, a CPU core will only ever > issue single reads to the external bus (unless you mark the memory > as cacheable, or perform a double-precision floating-point read). > If you want to improve speed, then you need to use DMA to move data > from the local bus to memory, and from there to the network. > > When I was looking at the 440EP, I ran some DMA tests to the PCI > connector on the Yosemite evaluation board ... > > http://www.ovro.caltech.edu/~dwh/powerpc_440ep.pdf > > You could do is to run some DMA tests to the local bus and probe the > bus with a scope to see that you are getting back-to-back reads. > > Assuming the ROACH interface to the PowerPC local bus is 16-bits at > 33MHz, you should be able to approach 50MB/s transfer rates. > > The FPGA-side of the local bus would need to implement burst > transactions; I don't recall the details of this processors local > bus (I ended up using a Freescale PowerPC instead). > > Cheers, > Dave > >
