I am beginning a project where I would like to use a rtl process as both a rt process and a driver for 4 ea. bt848 devices. I need 12 buffers of 172,800 bytes ea. and each buffer needs to be DMA capable (consecutive physical addresses). I could live with the buffers being fragmented - meaning that each buffer might in turn be composed of smaller buffers - but it would make more sense (to me) if each buffer was the size that was really needed. I mention this because it is also my understanding that the maximum memory that can be allocated at any one time using get_free_page () is 128KB.
I wish to do all processing in a Linux process. So it would be real nice if I could also access the buffers from my Linux process rather than having rtl (or a driver) set up the bt848 DMA controllers and then have to copy the buffers to another set of 12 buffers in user-land. Sounds like a candidate for shared memory, except that it is my understanding that memory allocated for shared memory is not physically consecutive and therefore not DMA capable.
One way that I hear of to do this might be to use the mem = xxxx at boot time , reserving the upper 2 MB of ram for my buffers and then hard code carve it up into the buffers that I need. I don't have any idea if these buffers could somehow be accessed from user-land or whether they would have to be copy_to_user()'d or similar.
Any suggestions? Good places to look and learn? Also, any corrections of my (mis)understandings would be greatly appreciated.
Thanks
Wayne E. Van Loon Sr.
