Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/dcc/limeric.cpp

@@ -0,0 +1,100 @@
+#include "limeric.hpp"
+#include <vanetza/common/runtime.hpp>
+#include <cassert>
+#include <cmath>
+#include <numeric>
+
+namespace vanetza
+{
+namespace dcc
+{
+
+static const Limeric::Parameters limericDefaultParams;
+
+Limeric::Limeric(Runtime& rt) : Limeric(rt, limericDefaultParams)
+{
+}
+
+Limeric::Limeric(Runtime& rt, const Parameters& params) :
+    on_duty_cycle_change(m_duty_cycle_change), m_runtime(rt), m_params(params),
+    m_duty_cycle(mean(params.delta_max, params.delta_min)), m_cbr(2)
+{
+    assert(m_cbr.empty());
+    schedule();
+}
+
+Limeric::~Limeric()
+{
+    m_runtime.cancel(this);
+}
+
+ChannelLoad Limeric::average_cbr() const
+{
+    if (m_cbr.full()) {
+        return 0.5 * mean(m_cbr.begin(), m_cbr.end()) + 0.5 * m_channel_load;
+    } else {
+        return m_channel_load;
+    }
+}
+
+void Limeric::update_cbr(ChannelLoad cbr)
+{
+    const bool full = m_cbr.full();
+    m_cbr.push_back(cbr);
+    if (!full) {
+        m_channel_load = mean(m_cbr.begin(), m_cbr.end());
+    }
+}
+
+UnitInterval Limeric::calculate_duty_cycle() const
+{
+    const double cbr_delta = m_params.cbr_target.value() - m_channel_load.value();
+    double delta_offset = 0.0;
+    if (cbr_delta > 0.0) {
+        delta_offset = std::min(m_params.beta.value() * cbr_delta, m_params.g_plus_max);
+    } else {
+        delta_offset = std::max(m_params.beta.value() * cbr_delta, m_params.g_minus_max);
+    }
+    UnitInterval delta = m_params.alpha.complement() * m_duty_cycle + delta_offset;
+    delta = std::min(std::max(delta, m_params.delta_min), m_params.delta_max);
+
+    if (m_dual_alpha) {
+        if (m_duty_cycle - delta > m_dual_alpha->threshold) {
+            delta = m_dual_alpha->alternate_alpha.complement() * m_duty_cycle + delta_offset;
+            delta = std::min(std::max(delta, m_params.delta_min), m_params.delta_max);
+        }
+    }
+    return delta;
+}
+
+void Limeric::calculate(Clock::time_point tp)
+{
+    m_channel_load = average_cbr();
+    m_duty_cycle = calculate_duty_cycle(); // uses m_channel_load
+    m_duty_cycle_change(this, tp);
+    schedule();
+}
+
+void Limeric::schedule()
+{
+    // schedule for next possible modulo 2 * cbr_interval (usually 200ms) time point
+    const Clock::duration scheduling_interval = 2 * m_params.cbr_interval;
+    Clock::time_point tp = m_runtime.now() + scheduling_interval;
+    const Clock::duration scheduling_bias = tp.time_since_epoch() % scheduling_interval;
+    if (scheduling_bias > m_params.cbr_interval) {
+        tp += scheduling_interval - scheduling_bias;
+    } else if (scheduling_bias > Clock::duration::zero()) {
+        tp -= scheduling_bias;
+    }
+    m_runtime.schedule(tp, [this](Clock::time_point tp) {
+        this->calculate(tp);
+    });
+}
+
+void Limeric::configure_dual_alpha(const boost::optional<DualAlphaParameters>& params)
+{
+    m_dual_alpha = params;
+}
+
+} // namespace dcc
+} // namespace vanetza