On Aug 9, 2019, at 2:34 PM, Charles Forsyth <charles.fors...@gmail.com> 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 <charles.fors...@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.fors...@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).
Thanks. Not ideal for plan9 but it would be nice to have access to all its IO capabilities over 9p.
