[lowrisc-dev] Re: [sw-dev] Is a de facto standard memory map
helpful or harmful?
arnd at arndb.de
Thu Jul 14 13:55:37 BST 2016
On Thursday, July 14, 2016 5:52:28 AM CEST krste at berkeley.edu wrote:
> | Unfortunately, the memory map described on page 12 of that document
> | makes the same mistake as some ARM64 chips and makes the RAM
> | location extremely sparse, with the first 14GB starting close to
> | zero, but all RAM beyond that starting at 0x1_0000_0000_0000
> | (256TB), which I guess requires using an extra level of page tables
> | for the kind of linear mapping that Linux has. It's probably too
> | late to change that, but I'd suggest that future implementations
> | do it differently.
> Platforms only need populate a single linear RAM address region. The
> memory map describes the options where this could be put.
> The reason we, and many others, adopt this style of layout is to
> reduce hardware costs for smaller implementations which do not need to
> provide all physical address bits and to support various DIMM sizes
> without adding complexity/delay to memory accesses and coherence
Ok, that makes sense, and only leaves the problem of relocating
the kernel at boot time to the correct physical address.
More information about the lowrisc-dev