Designing advanced DSP applications on the Kinetis Cortex-M4 MCU

Comparing the measures and simulated values of the execution time for fast current control loop of PMSM sensorless vector control, we get 20% to 40% worse performance, depending on the function (for example Space Vector Modulation algorithm contains more branches than PID regulator, therefore is the performance more affected). There are possibilities to minimize this unfavorable behavior.

The developer should avoid function calls in the time-critical part of the code. One of the options is also to copy the whole code, or part of the code (the most time-critical function) to the program RAM, just after the application start. In that case, changes in linker file have to be made. The developer has to put the function at an absolute location in the flash memory to be able to copy it to RAM.

Rich peripherals set of the Kinetis MCU family

As can be seen from the results of the execution time calculation and measurement of sensorless PMSM vector control algorithm, microcontrollers with Cortex-M4 core are capable of using in the application areas where the DSP functionalities are required. Of course, the sensorless PMSM vector control can be made also with a 16-bit DSC or even a general purpose MCU, so it doesn’t bring significant effect to use a Cortex-M4 processor solely for driving the motor.

But the rich peripherals set of the Kinetis MCU family and sufficient margin of computation performance makes it possible for the developer to enhance the application to different kinds of communication as well as visualization via graphic or segment LCD.

References

1. ARMv7-M Architecture Reference Manual, ARM Limited, 2010

2. Application Note 33 Fixed Point Arithmetic on the ARM, Advanced RISC Machines Ltd (ARM), 1996

3. Sensorless PMSM Vector Control with a Sliding Mode Observer for Compressors Using MC56F8013, Freescale Semiconductor, 2008

4. Sensorless PMSM Control for an H-axis Washing Machine Drive, Freescale Semiconductor, 2010

5. Advanced Control Library for 56800E, User reference manual, Freescale Semiconductor, 2009

* * Matus Plachy is with Freescale Semiconductor; Anders Lundgren, and Lotta Frimanson are with IAR Systems.

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