A controller and a memory-access method for use in the controller are provided. The controller includes a sensor-processing system, and the sensor-processing system includes a memory, and a buffer, wherein the controller is coupled to an external memory and a sensor. The method includes the steps of: gathering the sensor data from the sensor and writing the gathered sensor data into the memory; writing information associated with the sensor data into the buffer; determining whether a fill level of the buffer has reached a predetermined threshold; and retrieving the sensor data from the memory and writing the retrieved sensor data to the external memory according to the information associated with the stored sensor data in the buffer when it is determined that the fill level has reached the predetermined threshold.