What is the difference between HAL and LL drivers in STM32?

 The HAL (Hardware Abstraction Layer) and LL (Low Layer) drivers in STM32 are both provided by STMicroelectronics, but they serve different levels of abstraction and are suited to different use cases.



Here’s a breakdown of their differences:

 HAL vs. LL: Key Differences

FeatureHAL (Hardware Abstraction Layer)LL (Low Layer)
Abstraction LevelHigh-level abstractionLow-level, close to register access
Ease of UseEasier for beginners and rapid developmentRequires deeper understanding of hardware
Code SizeLarger (more layers, more function calls)Smaller and more efficient
PerformanceSlower due to overheadFaster and closer to bare-metal speed
PortabilityMore portable across STM32 familiesLess portable, tied closely to registers
FlexibilityLimited to what's implemented in HAL functionsMore control and customization
Interrupt HandlingAbstracted and simplifiedMust be configured manually
Generated by CubeMXYes (fully supported)Yes (partial support)

 When to Use HAL

  • You're building general-purpose applications

  • You want to prototype quickly

  • You're less experienced with STM32 hardware

  • Code portability and readability are more important than performance

 When to Use LL

  • You need higher performance and tight control

  • You're working on time-critical applications (e.g., motor control, real-time processing)

  • You want minimal code size

  • You're familiar with STM32 register-level programming

 Can You Mix HAL and LL?

Yes! STM32Cube allows mixing HAL and LL drivers in the same project. This is common when:

  • Most of your code uses HAL for simplicity

  • Specific performance-critical parts use LL (e.g., high-speed ADC, DMA, or GPIO toggling)

 Example

Toggle GPIO Pin

  • HAL:

    c

    HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_SET);

  • LL:

    c

    LL_GPIO_SetOutputPin(GPIOA, LL_GPIO_PIN_5);

 Summary

NeedUse
Simplicity & portabilityHAL
Speed & efficiencyLL
Fine-grained hardware controlLL
Mix of ease and controlHAL + LL (hybrid)

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