为何选择Cortex-M4内核

　　The ARM Cortex-M4 processor is the latest embedded processor by ARM specifically developed to address digital signal control markets that demand an efficient， easy-to-use blend of control and signal processing capabilities in microcontroller applications. The combination of high-efficiency signal processing functionality with the low-power， low cost and ease-of-use benefits of the Cortex-M family of processors is designed to satisfy the emerging category of flexible solutions specifically targeting the motor control， automotive， power management， embedded audio and industrial automation markets. The Cortex-M4 processor extends the use of Cortex-M cores to applications that require more computational performance than available currently with Cortex-M3. The Cortex-M4 features a single-cycle multiply-accumulate （MAC） unit， optimized single instruction multiple data （SIMD） instructions， saturating arithmetic instructions and an optional single precision Floating-Point Unit （FPU）。 So， the Cortex-M4 is a Cortex-M3 with the DSP instruction add-ons， and migrating from Cortex-M3 to Cortex-M4 is very easy