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direct memory access possible?

Posted:
Thu Aug 22, 2013 1:34 pm
by Gravis
is it possible (with it's current configuration) to directly access the RAM on the Parallella from the Epiphany? I'm interested in bypassing the ARM for increased I/O speed.
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 2:16 pm
by ysapir
The Epiphany works in the physical memory space. You can address (almost) any memory location on the board directly. Doing so outside of the EMEM range may crash your Linux system.
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 5:00 pm
by Gravis
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 5:10 pm
by ysapir
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 5:40 pm
by Gravis
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 5:51 pm
by ysapir
As stated above, the Epiphnay works in the physical address space. Out of the 32-bit (4GB) space, there are a few 1MB slices assigned to physical eCores. The system's DRAM consumes so-and-so memory as well, out of the same 4GB pool. In the Parallella, the first 1GB of memory space is occupied by the physical DRAM. The space starting at 0x80800000 is occupied by the Epiphany.
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 7:25 pm
by Gravis
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 7:48 pm
by ysapir
The entire space is not "taken". Part of it is allocated for the Epiphany chip. Both ARM and Epiphany "see" the same 4GB space. However, in your ARM Linux program, you don't "see" this space directly. You "see" the virtual address space, and you need mappings to "get out" to physical space.
Re: direct memory access possible?

Posted:
Thu Aug 22, 2013 8:48 pm
by Gravis
Re: direct memory access possible?

Posted:
Fri Aug 23, 2013 11:51 pm
by Gravis
umm... hello?