Thank you very much. Can I write the code in user space? Or I have to
write a kernel driver to reach the highest speed? What about the speed
difference between user space and kernel space?
Thanks,
Zhaomin
--- In David Hawkins <> wrote:
>
> I wrote a test to toggle the bits in XDIO#1.
>
> With the loop
>
> while(1) {
> *port = 0;
> *port = 0xFF;
> }
>
> and optimization on, the code disassembles into
> a 3-line loop containing strb, strb, and b.
> Thats about the smallest loop you'll get.
>
> The I/O toggled at 3.5MHz, i.e., about 285ns period.
> So, each write low or high takes about half that.
>
> Assuming the XDIO control port is a typical register,
> then 7MHz is the fastest rate you write to the FPGA,
> i.e., 7MB/s for a byte-wide register, 14MB/s for a
> 16-bit wide register.
>
> If a 24MHz sensor with 8-bit data has a continuous
> data rate of 24MB/s, you're out of luck!
>
> However, an image could be captured into a buffer, and
> then transmitted to the ARM;
>
> capture time: 1.3Mpixels / 24MHz = 54.2ms
> transfer time: 1.3Mpixels / 14MB/s = 92.8ms
>
> But, the Cyclone doesn't have 1.3MB of memory,
> so you'd have to buffer the data into the SDRAM.
> Which means you'd need to check that its bus bandwidth
> can hit 24MB/s; which I'm pretty sure it can since its
> clocked at 75MHz and is 16-bits wide.
>
> So given that you have to send data to SDRAM, and then
> read from SDRAM, your time for 1 image is at best
> about 150ms, or about 6 frames per second.
>
> Of course if you could slow the sensor clock to say 5MHz,
> then you could probably do this with the XDIO.
>
> Hope that helps.
> Dave
>
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