Re: Plan 9 C compiler for Xtensa CPUs

For IoT deployments, I suppose that one processor core on the ESP32 could
run the WiFi / networking stack and the other act as a CPU-like server and
thus run a small number of servers to expose the interface(s) in a 9P
mountable fashion to more powerful nodes.  A RT-ish kernel might suffice in
most practical use cases - it is IoT after all.  In my vision for Plan9 IoT
I never considered running file-server or terminal server on ESP-32
hardware. There are more capable nodes which would be better suited for
those purposes.  Of course, these observations presume that the 9p protocol
provides sufficient security against any ESP-32 node going rogue for
whatever reason.

It has been said :  "The 'S' in IoT stands for security".  If Plan9 can
address that deficiency of the current state of the art for IoT devices,
then it would be a worthwhile exercise.

On Mon, 19 Aug 2019 at 00:12, Charles Forsyth <[email protected]>
wrote:

> There is another existing variant of ESP32 with flash and RAM, and that
> one would provide the external memory MMU.
> It seems there could be a range from a small RT-ish kernel, with and
> without a user mode, on little ESP32, to a Plan 9 kernel with a few
> specialised processes on the bigger one.
> An Inferno-like system might also straddle the boundaries.
>
> On Sat, Aug 10, 2019 at 5:18 PM Charles Forsyth <[email protected]>
> wrote:
>
>> At a glance it looked as though the MMUs for the on-chip stuff were more
>> suitable for Unix Seventh Edition (no later) than "full" Plan 9.
>> The MMU for the external memory looked fine, but as I said, the device
>> I've got, and several other boards based on WROOM seem not
>> to bother with external memory. I didn't look widely, though.
>>
>> The processor is adequate, I think, but double == float (there's only
>> single precision).
>>
>> The existing systems use one processor for applications, and the other
>> mainly for communications.
>>
>> I haven't had a lot of spare time, but I did the assembler and am about
>> 3/4 through the loader.
>> For the most part it's a straightforward RISC.
>> Might do the disassembler next to help debug the rest, and finally the
>> compiler.
>>
>> On Sat, Aug 10, 2019 at 10:11 AM Cyber Fonic <[email protected]>
>> wrote:
>>
>>> The emergent problem with IoT is the lack of security.  From my
>>> understanding of Plan9's architecture. 9p protocol and the "root-less"
>>> security model suggests to me that a Plan9 swarm of IoT devices could be
>>> the "killer app" where Plan9 emerges on the strength of the vision of
>>> decades ago.  Looking at other RT OSes the security models are often bolted
>>> on.  Plan9 worked well on IBM PC era hardware. An ESP-32 has more resources
>>> and better networking than the early PCs.  From my tinkering and reverse
>>> engineering of IoT devices, almost all use 8266 based WiFi and often in
>>> conjunction with a uController. An ESP-32 is dual processor and with
>>> sufficient I/O for most simple tasks.  With IoT, in general, you don't need
>>> a lot of I/O, you simply throw more CPUs into the mix.
>>>
>>> On Sat, 10 Aug 2019 at 08:55, Skip Tavakkolian <
>>> [email protected]> wrote:
>>>
>>>> I'm not sure if the effort would be worth it; but if you add support
>>>> for esp32, I think it would be better for the os to be something like the
>>>> one you had in kencc for AVR (*) or possibly Russ' libtask, rather than
>>>> Plan 9. Staying with FreeRTOS would need removal of GCC specific things
>>>> from OS and dealing with lots of drivers in C++.
>>>>
>>>> The Cortex-M based mpus (e.g. Teensy 4 with Cortex M7 @ 600MHz) seem
>>>> more appropriate for an "embedded" Plan 9.
>>>>
>>>> (*) for those who have not seen it, it is here:
>>>> % ls -l /n/sources/contrib/forsyth/avr*
>>>> --rw-rw-r-- M 518 bootes sys 251227 Sep  4  2011
>>>> /n/sources/contrib/forsyth/avr.9gz
>>>>
>>>> On Fri, Aug 9, 2019 at 2:36 PM Charles Forsyth <
>>>> [email protected]> wrote:
>>>>
>>>>> 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 <
>>>>> [email protected]> 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 <
>>>>>> [email protected]> 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 <[email protected]>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> esp32 doesn’t have an mmu, right?
>>>>>>>>
>>>>>>>> On Jul 26, 2019, at 03:30, Charles Forsyth <
>>>>>>>> [email protected]> 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 <[email protected]>
>>>>>>>> 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?
>>>>>>>>>
>>>>>>>>>