[lowrisc-dev] Re: [sw-dev] Is a de facto standard memory map helpful or harmful?

Krste Asanovic krste at berkeley.edu
Wed Jul 13 13:59:29 BST 2016


Config string is supposed to provide this information.  We have code to parse and package this for Linux.  OS ports should all use this and the SBI to avoid binding to absolute physical addressees. 

Krste (on iPhone, forgive terseness)



> On Jul 13, 2016, at 8:48 AM, Alex Bradbury <asb at asbradbury.org> wrote:
> 
> One issue that's come up while chatting to people here at the RISC-V
> workshop in Boston is avoiding needless arbitrary differences between
> platforms. Having different memory maps is an example of this (e.g.
> having the PLIC instantiated with a different base offset). However,
> there also seems to be the view that some RISC-V implementers will be
> unable or unwilling to conform to a shared standard memory layout.
> Given this is the case, do we risk actually increasing fragmentation
> in the community by exposing memory map details to OS porters and
> low-level system programmers as they may come to rely on them? Are
> there any other advantages in retaining full flexibility for hardware
> implementers to modify their memory map at will?
> 
> Should if be RISC-V best practice that any OS porting work doesn't
> rely on a fixed memory map, and instead finds it at boot time through
> a device tree or device tree-like description? In cases where this
> doesn't make case an appropriate C header could be generated from that
> description, but the principle that the map isn't hardcoded in the OS
> codebase remains. I'm of course thinking beyond Linux here - it would
> seem a shame if it ended up that the seL4, FreeRTOS, ... ports did not
> work out of the box with any RISC-V implementation.
> 
> Best,
> 
> Alex
> 
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