Performance Metrics and Common Testing Tools for MCU CPUs

Common Performance Metrics for MCU CPUs

1. Basic Performance Metrics

Clock Frequency

• System Clock Frequency: 48MHz, 72MHz, 168MHz, 400MHz, etc.
• Internal Oscillator Accuracy: ±1%, ±2%, etc.
• External Crystal Support: Range of 4-25MHz
• PLL Multiplication Capability: Maximum multiplication factor

Instruction Execution Performance

• DMIPS/MHz: Dhrystone MIPS per MHz
• ARM Cortex-M0: ~0.9 DMIPS/MHz
• ARM Cortex-M3: ~1.25 DMIPS/MHz
• ARM Cortex-M4: ~1.25 DMIPS/MHz
• ARM Cortex-M7: ~2.14 DMIPS/MHz
• CoreMark/MHz: Modern benchmark score
• Instruction Set Efficiency: Thumb-2, RISC-V RV32I, etc.

2. Memory Performance

Flash Performance

• Read Wait States: 0-15 wait states
• Prefetch Buffer: Support for instruction prefetch
• Flash Accelerator: Technologies like ART, Prefetch, etc.
• Code Execution Speed: Performance of executing directly from Flash

SRAM Performance

• Zero Wait Access: SRAM typically has 0 wait states
• TCM (Tightly Coupled Memory): Tightly coupled memory
• Multi-Bank Design: Parallel access capability

Cache Performance (High-end MCUs)

• Instruction Cache Hit Rate: Typically >90%
• Data Cache Hit Rate: Varies by application
• Cache Size: 4KB-64KB

3. Real-Time Performance Metrics

Interrupt Response

• Interrupt Latency: 12-16 clock cycles
• Interrupt Nesting Depth: Supported levels of nesting
• Number of Priorities: 4-256 priorities
• Tail-Chaining Interrupts: Optimization for consecutive interrupt handling

Task Switching

• Context Switch Time: Microsecond level
• Register Save/Restore: Automatic/Manual
• Stack Pointer Switching: PSP/MSP switch time

4. Mathematical Operation Performance

Integer Operations

• 32-bit Multiplication: Single-cycle or multi-cycle
• Division Performance: Hardware divider support
• Bit Operations: CLZ, REV, etc.

Floating Point Operations (MCUs with FPU)

• Single Precision Floating Point: IEEE 754 standard
• Double Precision Support: Available in some high-end MCUs
• Floating Point Instruction Latency: 1-14 clock cycles
• DSP Instructions: SIMD, MAC, etc.

5. Power Consumption Performance

Dynamic Power Consumption

• Operating Mode Power Consumption: µA/MHz
• Peripheral Power Consumption: Power contribution from various peripherals

Low Power Modes

• Sleep Mode: CPU stops, peripherals run
• Stop Mode: Most clocks stop
• Standby Mode: Lowest power mode
• Wake-Up Time: Time to recover from low power mode

Open Source Performance Testing Tools

1. Comprehensive Performance Benchmarking

CoreMark

Dhrystone

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// Classic integer performance test
// Outputs DMIPS (Dhrystone MIPS)
#include "dhry.h"
void dhrystone_test(void) {
    // Execute Dhrystone benchmark
}

Whetstone

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// Floating point performance test (for MCUs with FPU)
// Outputs MWIPS (Million Whetstone Instructions Per Second)

2. Real-Time Performance Testing Tools

rt-tests

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# Real-time performance testing in Linux environment
git clone git://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git
cd rt-tests
make
./cyclictest -p 80 -n -i 10000 -l 10000

MCU-Specific Interrupt Latency Testing

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// Custom interrupt response time test
void interrupt_latency_test(void) {
    // Configure GPIO and timer
    // Measure delay from external signal to interrupt handling
}

3. Memory Performance Testing

STREAM Benchmark (Improved version for MCUs)

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// Memory bandwidth test
void stream_test(void) {
    // Copy: a[i] = b[i]
    // Scale: a[i] = q*b[i]  
    // Add: a[i] = b[i] + c[i]
    // Triad: a[i] = b[i] + q*c[i]
}

Memory Test

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// Memory access pattern test
void memory_pattern_test(void) {
    // Sequential access
    // Random access
    // Stride access
}

4. Floating Point Performance Testing Tools

Linpack (MCU version)

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// Linear algebra operation performance
void linpack_test(void) {
    // Solve linear equations
    // Output MFLOPS
}

FFT Benchmark

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// Using CMSIS-DSP library
#include "arm_math.h"
void fft_performance_test(void) {
    arm_cfft_f32(&arm_cfft_sR_f32_len1024, testInput_f32_10khz, 0, 1);
}

5. Power Analysis Tools

EnergyTrace (TI)

• Hardware tool, but has open-source analysis software
• Real-time power monitoring

Power Profiler Kit (Nordic)

• Open-source host software
• Accurate current measurement

Custom Power Testing

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// Software power benchmark test
void power_benchmark(void) {
    // Power testing under different workloads
    // CPU-intensive tasks
    // I/O-intensive tasks
    // Mixed load
}

6. Open Source MCU Benchmark Suites

EEMBC IoTMark

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# IoT device performance benchmark
git clone https://github.com/eembc/iotmark.git
# Needs to be ported to target MCU platform

MiBench (Embedded version)

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# Embedded system benchmark suite
git clone https://github.com/MiBench/MiBench.git
# Includes tests for various application scenarios

TinyMLPerf

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# Machine learning inference performance testing
git clone https://github.com/mlcommons/tiny.git
# Suitable for MCUs that support AI acceleration

7. Custom Performance Testing Framework

MCU Performance Test Suite

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typedef struct {
    char* test_name;
    void (*test_func)(void);
    uint32_t iterations;
    uint32_t expected_cycles;
} perf_test_t;

void run_performance_suite(void) {
    perf_test_t tests[] = {
        {"Integer Math", integer_math_test, 10000, 0},
        {"Float Math", float_math_test, 1000, 0},
        {"Memory Copy", memory_copy_test, 1000, 0},
        {"GPIO Toggle", gpio_toggle_test, 100000, 0}
    };

    for(int i = 0; i < sizeof(tests)/sizeof(tests[0]); i++) {
        measure_performance(&amp;tests[i]);
    }
}

8. Cross-Compilation and Porting Considerations

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# Compilation options for ARM Cortex-M
CFLAGS += -mcpu=cortex-m4 -mthumb -mfpu=fpv4-sp-d16 -mfloat-abi=hard
CFLAGS += -O2 -g -Wall
CFLAGS += -DCOREMARK_ITERATIONS=1000

These tools and metrics can help you comprehensively evaluate the CPU performance of MCUs, select the appropriate MCU, and optimize application performance.