This is the preliminary work for editing the source via gcs. Look at line 170++. If not script is running, the module reacts on commands written by the gcs to picocstatus.Command. It should be used to up- and download the source sector wise. Filesystem  is controlled by the module itself. All you have to do is to give the file a number und initiate the saving process.
It is also prossible to transfer sources via us art and control commands. picoC itself doesn't need a usart for running.