Hello Huang,
Regarding your question with the FRDM-K64F and FRDM-FXS-MULT2-B boards, my recommendation would be to use the open SDA from Segger instead of the one from MBED, since the first one allow you to do more things, such as copying the binary FSFK-K64F-FXS-NML-NED into the Freedom.
I will attached the firmware you need so you can upload it to the FRDM-K64F. Also in the following link you will find a detailed document that explains how to load this new firmware into your board. Specifically Chapters 2.1 and 2.2 will be very helpful.
http://www.nxp.com/assets/documents/data/en/user-guides/OPENSDAUG.pdf
Once the new Segger firmware is installed you may need to follow these steps in order to make the Sensor Fusion Toolbox, work along with the two boards you have.
- Go to the Installation folder from the Senor Fusion Toolbox. In my case is C:\Program Files (x86)\NXP\NXP Sensor Fusion Toolbox
- Go to the search bar top right and look for the binary file FSFK-K64F-FXS-NML-NED
- Drag and drop the file mentioned as the image below:

Please let us know if it worked and if it didn’t, don’t hesitate in contacting us back so we can address the issue or solve any other problem you may have.
Regards.