ROACH bus runs at 66MHz (or 83MHz if you "overclock" it to boot config
H). I agree that the 3.5MB/s is miserable performance considering what
it should be capable of achieving. I suspect these bottlenecks are
mostly BORPH related. I also recall an extended bus handshake being
mentioned for every bus transaction. Dave G, Marc or Shanly might be
able to comment further. I believe Shanly has been working on some
optimisation in BORPH. Dave, what speeds can you get through uboot? Is
there room for optimisation here? I would also welcome a speedup.
Jason
On 28 Apr 2010, at 20:11, David MacMahon wrote:
Hi, Mel,
On Apr 28, 2010, at 9:54 , melvyn wright wrote:
You should be getting around 7MegaBytes/s across that bus.
56 Mb / 16 b < 4 MHz << bus clock frequency
Good suggestion re kernel, but don't understand the significance of
the 56 Mb
I omitted the "/s" in "56 Mb/s". 7 megabytes/s == 56 Megabits/s.
Since the bus to the FPGA is 16 bits wide, dividing by 16 gives the
number of 16 bit words transferred per second as around 3.5
million. I don't know the frequency at which the bus runs, but I
suspect it is far greater than 3.5 MHz hence my comment about room
for improvement.
Dave
P.S. I don't know how conventional or official it is, but I use
lowercase 'b' for "bit" and uppercase 'B' for "byte".
