arm: async echo app

arm/trace.cc

@@ -0,0 +1,38 @@
+#include "trace.h"
+
+#include <algorithm>
+
+#include "itoa.h"
+#include "lock.h"
+#include "uart.h"
+
+namespace tracing {
+namespace {
+
+constexpr size_t kTraceBufferSize = 256;
+std::array<TraceEvent, kTraceBufferSize> buffer;
+size_t write_ptr = 0;
+
+}  // namespace
+
+void trace(int raw_event) { trace(static_cast<TraceEvent>(raw_event)); }
+
+void trace(TraceEvent event) {
+    InterruptLock lock;
+
+    buffer[write_ptr] = event;
+
+    write_ptr = (write_ptr + 1) % buffer.size();
+}
+
+void dump() {
+    std::rotate(buffer.begin(), buffer.begin() + write_ptr, buffer.end());
+
+    char number[] = "00000000\r\n";
+
+    for (TraceEvent event : buffer) {
+        itoa(static_cast<int>(event), number);
+        UartSendCrash(number);
+    }
+}
+}  // namespace tracing