GeezerVison

static bool synthio_envelope_state_step(synthio_envelope_state_t *state, synthio_envelope_definition_t *def, size_t n_steps) {
    state->substep += n_steps;
    while (state->substep >= SYNTHIO_MAX_DUR) {
        // max n_steps should be SYNTHIO_MAX_DUR so this loop executes at most
        // once
        state->substep -= SYNTHIO_MAX_DUR;
        switch (state->state) {
            case SYNTHIO_ENVELOPE_STATE_SUSTAIN:
                break;
            case SYNTHIO_ENVELOPE_STATE_ATTACK:
                state->level = MIN(state->level + def->attack_step, def->attack_level);
                if (state->level == def->attack_level) {
                    state->state = SYNTHIO_ENVELOPE_STATE_DECAY;
                }
                break;
            case SYNTHIO_ENVELOPE_STATE_DECAY:
                state->level = MAX(state->level + def->decay_step, def->sustain_level);
                if (state->level == def->sustain_level) {
                    state->state = SYNTHIO_ENVELOPE_STATE_SUSTAIN;
                }
                break;
            case SYNTHIO_ENVELOPE_STATE_RELEASE:
                state->level = MAX(state->level + def->release_step, 0);
                if (state->level == 0) {
                    return false; // Indicate that note envelope has completed
                }
        }
    }
    return true;
}

    // advance envelope states
    for (int chan = 0; chan < CIRCUITPY_SYNTHIO_MAX_CHANNELS; chan++) {
        mp_obj_t note_obj = synth->span.note_obj[chan];
        if (note_obj == SYNTHIO_SILENCE) {
            continue;
        }
        if (!synthio_envelope_state_step(&synth->envelope_state[chan], synthio_synth_get_note_envelope(synth, note_obj), dur)) {
            // Envelope has completed, go ahead and reset channel
            synth->span.note_obj[chan] = SYNTHIO_SILENCE;
        }
    }

channels filled: 14
still pressed after decay: 0
a further press after decay is accepted: True

case SYNTHIO_ENVELOPE_STATE_DECAY:
    state->level = MAX(state->level + def->decay_step, def->sustain_level);
    if (state->level == def->sustain_level) {
        if (state->level == 0) {
            return false;
        }
        state->state = SYNTHIO_ENVELOPE_STATE_SUSTAIN;
    }
    break;