Sleep with __wfi() between USB interrupts instead of busy-polling

picomap.cpp

@@ -57,10 +57,9 @@ int main() {
     while (true) {
         tud_task();
 
-        if (!tud_cdc_available()) continue;
-
+        while (tud_cdc_available()) {
             uint8_t byte;
-        if (tud_cdc_read(&byte, 1) != 1) continue;
+            if (tud_cdc_read(&byte, 1) != 1) break;
 
             rx_buf.push_back(byte);
 
@@ -90,4 +89,7 @@ int main() {
             }
             }
         }
+
+        __wfi();
+    }
 }