extract debug_log into its own static library; expose log_view iterator instead of raw ring_buffer

debug_log/debug_log.h

@@ -0,0 +1,52 @@
+#pragma once
+#include <cstdint>
+#include <string>
+#include <string_view>
+#include "pico/time.h"
+
+struct log_entry {
+    uint32_t timestamp_us;
+    std::string message;
+};
+
+class log_iterator {
+    const log_entry* data;
+    uint16_t base;
+    uint16_t cap;
+    uint16_t pos;
+public:
+    log_iterator(const log_entry* d, uint16_t b, uint16_t c, uint16_t p)
+        : data(d), base(b), cap(c), pos(p) {}
+    const log_entry& operator*() const { return data[(base + pos) % cap]; }
+    log_iterator& operator++() { ++pos; return *this; }
+    bool operator!=(const log_iterator& o) const { return pos != o.pos; }
+};
+
+class log_view {
+    const log_entry* data;
+    uint16_t base;
+    uint16_t cap;
+    uint16_t count;
+public:
+    log_view(const log_entry* d, uint16_t b, uint16_t c, uint16_t n)
+        : data(d), base(b), cap(c), count(n) {}
+    log_iterator begin() const { return {data, base, cap, 0}; }
+    log_iterator end() const { return {data, base, cap, count}; }
+};
+
+log_view log_entries();
+
+void dlog(std::string_view msg);
+
+__attribute__((format(printf, 1, 2)))
+void dlogf(const char* fmt, ...);
+
+template <typename F>
+inline void dlog_if_slow(std::string_view label, uint32_t threshold_us, F&& fn) {
+    uint32_t t0 = time_us_32();
+    fn();
+    uint32_t elapsed = time_us_32() - t0;
+    if (elapsed > threshold_us) {
+        dlogf("%.*s %luus", static_cast<int>(label.size()), label.data(), static_cast<unsigned long>(elapsed));
+    }
+}