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Read the learning points of the ametal_hc595 interface
The eighth chapter delves into a deeper understanding of AMetal, specifically focusing on the HC595 interface. This section explores how the HC595, a serial-to-parallel peripheral, can be controlled using GPIO or SPI interfaces to simplify driver implementation.
In order to abstract the differences in data output modes, the HC595 interface can be designed similarly to the universal LED interface. This approach ensures consistency and ease of use across different hardware components.
When defining the interface for HC595, it is common to prefix the function names with "am_hc595_", such as am_hc595_send(), which sends data to the device. Additionally, functions like am_hc595_enable() and am_hc595_disable() control the output state by managing the OE pin.
For parameters, instead of using an ID number to distinguish multiple HC595 devices, a more efficient approach involves using a handle—a pointer to the object. This handle allows direct access to the HC595 instance without the need for searching, significantly improving performance.
The send function, am_hc595_send(), requires additional parameters to specify the data being sent, such as a pointer to the data and the number of bytes. This design allows for flexibility, especially when multiple HC595s are cascaded to support more bits.
The return value of all interfaces is typically defined as an integer error code, ensuring standardization and ease of debugging.
In implementing the interface, an abstract HC595 device class is created to encapsulate the hardware-specific functions. These functions are stored in a virtual function table, allowing for polymorphic behavior and easy extension.
A specific HC595 device class, derived from the abstract class, implements the required functions based on the actual hardware. For example, when using SPI to control the HC595, the device needs information such as the latch pin, output enable pin, and SPI clock frequency.
The bit order during data transmission is also important, as it determines the output sequence of the HC595. Users must specify this order to ensure correct functionality.
To facilitate this, a device information structure is used to store all necessary details. The initialization function sets up the device, assigning each member variable and returning a handle that can be used with the general HC595 interface.
Overall, the design of the HC595 interface emphasizes efficiency, abstraction, and flexibility, making it easier to integrate into various applications and systems.