Add Elixir ESP NVS example

[mnishiguchi]

I tested it with my ESP32-S3 + v0.6.6 image.

Here is example log output:

AtomVM init.
I (609) sys: Loaded BEAM partition main.avm at address 0x250000 (size=1048576 bytes)
Starting application...
Loading count from NVS ...
Loaded count: 313
This device has restarted 314 time(s).
Saving count to NVS ...
Restarting in 10 seconds ...

[petermm]

Thank you!

I'm not sure we want to show writing this much to nvs - see the warning here: https://doc.atomvm.org/latest/programmers-guide.html#non-volatile-storage

Maybe change it to RTC https://doc.atomvm.org/latest/programmers-guide.html#rtc-memory - which obviously doesn't survive power outs, but doesn't wear down the flash..

[mnishiguchi]

Oh that makes sense — frequent writes to NVS are a bad pattern. I can convert the counter to RTC and revise the NVS usage to something that doesn’t write often, resulting in two examples.

[petermm]

yeah, remember to try/catch the rtc_slow_get_binary() - as it will raise badarg when not set eg for you on first boot..

[mnishiguchi]

Thanks for the feedback.

I updated the examples to avoid frequent NVS writes:

• EspNvs now writes the default value only once (when the key is missing) and then just logs the fetch result before restarting.
• The restart counter example was moved to EspRtc using RTC slow memory (so it survives software resets without wearing flash).

Example output:

EspNvs:

Fetched word from NVS: AtomVM
Restarting in 10 seconds ...

EspRtc:

Loading count from RTC slow memory ...
This device has restarted 2 time(s).
Saving count to RTC slow memory ...
Restarting in 10 seconds ...

[UncleGrumpy]

I'm not sure we want to show writing this much to nvs - see the warning here: https:

Excellent point! I should have caught this.

[mnishiguchi]

We could also add standardized .gitignore and .formatter.exs files across all Elixir examples for consistency.

Potentially .tool-versions as well.

[mnishiguchi]

I'm wondering what the ideal name for the RTC slow memory example would be. Should we use something more specific, like EspRtcSlowMemory?

[UncleGrumpy]

I'm wondering what the ideal name for the RTC slow memory example would be. Should we use something more specific, like EspRtcSlowMemory?

I think EspRtcMemory is good.

[UncleGrumpy]

We could also add standardized .gitignore and .formatter.exs files across all Elixir examples for consistency.

Potentially .tool-versions as well.

I would not add .tool-versions, this should be up to the users choice.

.gitignore is fine, but for simplicity I would prefer just one set of rules in the root directory, it can get harder to keep track of individual files through the directory tree.

I am not sure if we need a formatter.exs, we just want to follow default formatting rules. But I am much more familiar with Erlang and erlfmt, which is what we use for all AtomVM org repos.

[petermm]

Agree, I suggest not handling the projectwide .gitignore here though - also something good about seeing the avm file in git diff etc. so maybe no .gitignore is needed..

[petermm]

nitpick:
I'm not a fan of a nested module - I would just defstruct count: 0 here and then use %__MODULE__{count: count} or %EspRtcMemory{count: count} ?

(but certainly a matter of taste, so I'm good with a nested module if that is preferred )