Add ESP32C3 RISC-V stub
diff --git a/include/kernel/serial.h b/include/kernel/serial.h
new file mode 100644
index 0000000..7e391db
--- /dev/null
+++ b/include/kernel/serial.h
@@ -0,0 +1,8 @@
+#pragma once
+
+/**
+ * Initialize the default serial device.
+ */
+void init_serial();
+void serial_put(char byte);
+void serial_write(char *string);