Cortex M0+ Image for MSP3

The Cortex-M0+ is an ultra-low power 32-bit ARM processor core licensed by Arm Holdings. It is aimed at microcontroller applications that require high efficiency and low cost. The M0+ core is designed to offer significantly better performance than 8- and 16-bit microcontrollers while maintaining low power consumption.

The Cortex-M0+ is widely used in various microcontrollers from different manufacturers. One popular series of microcontrollers that uses the M0+ core is the MSP430 from Texas Instruments. The MSP430 is a 16-bit RISC-based microcontroller family that is optimized for low power consumption.

To use the Cortex-M0+ core in an MSP430 microcontroller, you need a Cortex-M0+ image that is compatible with the MSP430. An image refers to the compiled binary file that contains the Cortex-M0+ core and any other necessary components to run it on the target microcontroller hardware.

Building the Cortex M0+ Image

Here are the main steps to build a Cortex-M0+ image that can run on an MSP430 microcontroller:

1. Obtain the Cortex-M0+ IP core from Arm or from your microcontroller vendor.
2. Obtain a software development kit (SDK) and toolchain that supports Cortex-M0+ development.
3. Create a board support package (BSP) for the target MSP430 microcontroller.
4. Configure the memory layout and interfaces for the target microcontroller.
5. Write C/C++ code to implement your application.
6. Compile the code using the toolchain to generate the Cortex-M0+ binary.
7. Link the compiled binary with the BSP and any libraries to generate the final image.

The first step is to obtain the RTL (register transfer level) code for the Cortex-M0+ core IP from Arm or your microcontroller vendor. This HDL code defines the hardware implementation of the processor.

Next, you need a Cortex-M0+ software development kit and toolchain. The SDK provides libraries and header files needed to build software for the M0+ core. The toolchain includes a C/C++ compiler, assembler, linker and debugger that targets the M0+ architecture. Popular options include ARM Keil MDK, IAR EWARM and GCC-based toolchains.

A board support package (BSP) contains target-specific code to configure and initialize the microcontroller’s peripherals and interfaces like clocks, memory, GPIO etc. It interfaces the generic Cortex-M0+ core to the specific MSP430 target board.

The memory layout maps the code and data sections from the compiled binary to the target’s physical memory space. This needs to be configured optimally for the specific microcontroller. For example, placing routines in internal RAM for faster execution.

Application code can be written in C or C++, taking advantage of the BSP and driver libraries provided by the SDK. The code must follow the Cortex-M0+ specific requirements like fixed interrupt vectors.

The toolchain compiles the code down to M0+ machine code. Cortex-M0+ has a streamlined Thumb-2 instruction set optimized for simplicity and efficiency.

Finally, the object files are linked together into an executable ELF image. The linker defines the memory layout and resolves external references between objects. The image can then be loaded onto the target microcontroller.

Key Considerations

Here are some key considerations when building a Cortex-M0+ image for an MSP430 target:

• Processor initialization – The image needs to setup the Cortex-M0+ core registers, clocks and memory interface correctly for the MSP430 at startup.
• Interrupt handling – The Cortex-M0+ and MSP430 have different interrupt architectures. This needs to be abstracted by the BSP.
• Peripheral access – The SDK needs to provide access to the various peripherals of the MSP430 through suitable driver libraries.
• Stack/Heap – The memory layout needs to allocate stack and heap space appropriately for the application.
• Power management – The image must integrate Cortex-M0+ sleep/wakeup functions with the MSP430 power management capabilities.
• Debugging support – Most SDKs provide debugging capability via IDEs, JTAG and SWD interfaces.
• Performance – The use of Cortex-M0+ specific instructions can optimize performance for some applications.

Paying attention to these aspects ensures that the Cortex-M0+ core functions correctly on the target MSP430 hardware with access to all peripherals and features.

Advantages of Using Cortex-M0+ with MSP430

Here are some of the benefits of using a Cortex-M0+ core on an MSP430 MCU:

• Higher performance – The 32-bit Cortex-M0+ architecture enables higher CPU speed compared to the 16-bit MSP430 cores.
• Advanced features – Cortex-M0+ supports more advanced features like single-cycle I/O, SysTick timer, nested vectored interrupts etc.
• Simpler programming – Cortex-M0+ has a unified programming model across all Cortex-M cores. Familiar ARM Thumb-2 instruction set.
• Ecosystem compatibility – Vast ecosystem of tools, RTOSes, middleware, libraries that target Cortex-M family is now accessible.
• Code reuse – Easy to reuse code written for other Cortex-M devices. Reduces software development time.
• Lower power – Cortex-M0+ implements features like low power idle mode for reduced power consumption.
• Lower cost – Cortex-M0+ cores have a simpler design and smaller silicon footprint, reducing overall MCU cost.

With the Cortex-M0+ image, developers can get the efficiency and power benefits of MSP430 MCUs combined with higher performance, better usability and reuse of a 32-bit ARM core. The Cortex-M0+ is well-suited for low-power embedded applications like IoT sensors, wearables, industrial automation etc.

Example Code

Here is some example code that initializes the Cortex-M0+ core and blinks an LED on an MSP430 Launchpad board: // MSP430F5529 Launchpad register definitions #define GPIO_PORT_P1 ((volatile unsigned int *)0x40004C00) #define GPIO_DIR_P1 ((volatile unsigned int *)0x40004C04) // System Initialization void system_init(void) { // Set up the microcontroller system. // PLL, WatchDog, enable Peripheral Clocks // Set clocking to run directly from external crystal/oscillator CSCTL0_H = CSKEY_H; // Unlock CS registers CSCTL1 = DCOFSEL_0; // Set DCO to 1MHz CSCTL2 = SELA_0 + SELS_3 + SELM_3; // Set ACLK = LFXTCLK = HFXTCLK CSCTL3 = DIVA_0 + DIVS_0 + DIVM_0; // Set all dividers CSCTL4 &= ~LFXTDRIVE_3; // Clear LFXT max drive capability CSCTL4 |= LFXTDRIVE_2; // Set LFXT max drive capability to medium CSCTL5 &= ~LFXTOFF; // Clear LFXT disable bit CSCTL0_H = 0; // Lock CS registers // Configure GPIO GPIO_DIR_P1 |= BIT0; // Set P1.0 to output direction // Switch on LED GPIO_PORT_P1 |= BIT0; } // Main function int main(void) { // Initialize the system system_init(); // Blink the LED while(1) { volatile unsigned int i; GPIO_PORT_P1 ^= BIT0; // Toggle P1.0 using XOR for(i = 20000; i > 0; i–); // Delay } return 0; }

The code initializes the Cortex-M0+ core clock module to use the external crystal oscillator directly. It sets up the GPIO and toggles an LED on and off within a loop, creating a blinking effect. With suitable porting of MSP430 peripheral libraries, we can build full-featured applications.

Testing the Image

To test the Cortex-M0+ image on the target MSP430 hardware, we need to load the compiled executable file onto the microcontroller’s memory and execute it. Some methods for loading and testing are:

• Flash programmer – Use a dedicated flash programming tool connected to a host PC to load the image via JTAG or SPI interface.
• Debugger – Debuggers like Keil ULINKplus or IAR Probe can directly load the image over SWD/JTAG and execute it.
• Bootloader – Have a bootloader like UART or I2C bootloader pre-programmed on the target, which can then load the image.
• IDE – Most IDEs support building, flashing and debugging programs on the target board.

After loading the image, we can step through the code in the debugger and verify the proper initialization of the Cortex-M0+ core and peripherals on reset. Setting breakpoints and watchpoints allows inspection of registers, memory and program flow during execution.

For a non-debug build, toggling GPIOs connected to LEDs is a good way to verify the proper functioning of the image. Special test modes can also be incorporated to output debug information over UART or other peripherals.

Profiling with tools like SEGGER Ozone and ARM Streamline allows performance measurements of code running on the target. The results help identify any laggy parts of the application that can be optimized further.

Automated tests form an integral part of the development process. Unit testing frameworks like Ceedling can execute tests on the target board itself to validate functionality and catch regressions early.

Thus, through a combination of techniques like debugging, instrumentation, profiling and testing, we can thoroughly validate and verify the Cortex-M0+ image on the target MSP430 hardware.

Conclusion

In summary, building a Cortex-M0+ image for MSP430 requires obtaining the core IP, SDK, toolchain and creating a suitable BSP and memory layout for the target microcontroller. Key considerations include low-level initialization, interrupt handling, peripheral access, power management and debugging support. The advantages of combining Cortex-M0+ with MSP430 include higher performance, easier development and better power efficiency. The image can be tested using debuggers, bootloaders, IDEs and automated testing frameworks. With the right approach, the Cortex-M0+ core enables developers to build high quality embedded applications leveraging the strengths of the MSP430 platform.