Re: [9fans] Plan 9 C compiler for Xtensa CPUs

[Charles Forsyth <charles.forsyth@gmail.com>]

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Since the resources are small if not tiny, a little systems analysis and
design is probably needed, but it looks like a bit of fun, until the
inevitable moment of "why am I here?".

On Fri, Aug 9, 2019 at 4:50 PM Charles Forsyth <charles.forsyth@gmail.com>
wrote:

> The device I've got is ESP32-WROOM-32. None of the boards I've seen that
> use it bother with external memory,
> so memory is limited, especially the way it's partitioned.
>
> On Fri, Aug 9, 2019 at 3:50 PM Charles Forsyth <charles.forsyth@gmail.com>
> wrote:
>
>> The ESP32 has got several MMUs. The characteristics are different
>> depending on the part that a given MMU accesses (flash, ROM, SRAM, external
>> memory).
>> Some things are accessed using Memory Protection Units instead, which
>> control access by Process ID, but don't do mapping. Others including some
>> of the SRAMs are accessed through
>> an MMU that can do virtual to physical mapping. The MMUs for internal
>> SRAM0 and 2 choose protection for a given physical page as none, one or all
>> of PIDs 2 to 7, with the virtual address that
>> maps to it. PIDs 0 and 1 can access everything. PID 0 can execute
>> privileged instructions.
>> A large chunk of SRAM (SRAM 1) has only Memory Protection and no
>> translation. The external memory MMU is the most general (most
>> conventional).
>>
>> On Fri, Aug 9, 2019 at 3:19 PM Bakul Shah <bakul@bitblocks.com> wrote:
>>
>>> esp32 doesn’t have an mmu, right?
>>>
>>> On Jul 26, 2019, at 03:30, Charles Forsyth <charles.forsyth@gmail.com>
>>> wrote:
>>>
>>> I was thinking of doing that since I've got an ESP-32 for some reason
>>>
>>> On Fri, Jul 26, 2019 at 7:38 AM Cyber Fonic <cyberfonic@gmail.com>
>>> wrote:
>>>
>>>> I was reading the post Why Didn't Plan 9 Succeed
>>>> <https://news.ycombinator.com/item?id=20527650> on Hacker News.
>>>>
>>>> Made me think that Plan 9 for IoT system of systems could be viable.
>>>>
>>>> To that end, ESP-32 modules look capable enough to run Plan 9, but is
>>>> there a Plan 9 C compiler for Xtensa ISA CPUs?
>>>>
>>>>

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