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

debug_log/debug_log.cpp

@@ -0,0 +1,28 @@
+#include "debug_log.h"
+#include <cstdarg>
+#include <cstdio>
+#include "ring_buffer.h"
+
+namespace {
+
+constexpr uint16_t LOG_CAP = 32;
+ring_buffer<log_entry, LOG_CAP> buf;
+
+} // namespace
+
+void dlog(std::string_view msg) {
+    buf.push_overwrite(log_entry{static_cast<uint32_t>(time_us_32()), std::string(msg)});
+}
+
+void dlogf(const char* fmt, ...) {
+    char b[128];
+    va_list args;
+    va_start(args, fmt);
+    vsnprintf(b, sizeof(b), fmt, args);
+    va_end(args);
+    dlog(b);
+}
+
+log_view log_entries() {
+    return log_view{buf.data.data(), buf.head, LOG_CAP, buf.used()};
+}