Jonathan Haws wrote:
All,
I have what may be an unconventional question:
Our application consists of data being captured by an FPGA, processed, and
transferred to SDRAM. I simply give the FPGA an address of where I want it
stored in SDRAM and it simply DMAs the data over and interrupts me when
finished. I then take that data and store it to disk.
I have code in user space that handles all of the writing to disk nicely and
fast enough for my application (I am capturing data at about 35-40 Mbytes/sec).
My question is this: is it possible to give a user-space pointer to the FPGA
to DMA to? It seems like I would have problems with alignment, address
manipulation, and a whole slew of other issues.
What would be the best way to accomplish something like that? I want to handle all the disk access in user-space, but I do not want to have to copy 40 MB/s from kernel space to user-space either.
You can maintain a DMA buffer in kernel, then mmap to user space. And
maybe you need some handshake between FPGA and the apps to balance input
datas with datas to disk.
I can maintain an allocated, DMA-safe buffer in kernel space if needed. Can I
simply get a user-space pointer to that buffer? What calls are needed to
translate addresses?
Use remap_pfn_range() in your kernel DMA buffer manipulation driver
.mmap() handler to export DMA buffer address to user space.
Tony
Thanks for the help! I am still a newbie when it comes to kernel programming,
so I really appreciate the help!
Jonathan
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