Previously _onSample() computed and stored a volatile float _sma_avg
on every sample (64 times/minute on core 0). The getter simply returned
that pre-computed value.
This commit inverts the responsibility:
- _sma_sum is now volatile uint16_t — the raw integer sum is the
cross-core shared state, written atomically by core 0 (single S16I
instruction on Xtensa LX7) and read by core 1.
- The float conversion (uint16_t → float multiply) is moved into
getCore0Util(), which is called rarely (once/minute for history,
on-demand for web requests). The multiply now happens on the core
that actually needs the result.
- _sma_avg is removed entirely, saving 4 bytes and one volatile float
store per sample from the hot path.
- The SMA update is rewritten as a single combined expression:
const uint16_t last = _sma_buf[_sma_idx];
_sma_buf[_sma_idx] = s8;
_sma_sum = (_sma_sum - last) + s8;
This produces a single write to _sma_sum instead of two (decrement
then increment), which is cleaner when _sma_sum is volatile.
The cross-core contract is unchanged: core 0 writes _sma_sum once per
sample; core 1 reads it in getCore0Util(). A 16-bit aligned store on
Xtensa LX7 is a single instruction, so no spinlock is needed.
Valentin V. Bartenev
482b31bc19