Here I have a Tmote Sky node. And I have printf the RSSI on the terminal. Now I want to store these RSSI data to my computer. I have tried cfs which is used to operate the external flash of a node. So how can I save the data to my computer with contiki.
/platform/sky/Makefile.common provides a target serialdump, which will also print the output to a file named serialdump-<current time>. Therefore you want to tun make serialdump TARGET=sky.
Or do you want to get the data from the external flash? In that case you need to add a function that dumps the file contents to the serial (e.g. when pushing the button or sending a special command via serial). You can then save that output to a file.