A Lightweight Framework for Embedded Systems

Introduction to mr-library

mr-library is a lightweight framework designed for embedded systems, providing a unified low-level driver device model and basic service functions. It features modular design, configurability, and extensibility, helping developers quickly build embedded applications.

The mr-library framework supports basic kernel features such as mutexes and object management. It integrates services like an asynchronous event-driven framework (event) and multi-timer software timers (soft-timer). It provides driver device models for common peripherals such as serial ports, SPI, I2C, ADC/DAC, allowing access to underlying hardware devices through a unified driver interface (open, close, ioctl, read, write), decoupling low-level drivers from applications.

Application Scenarios

• Low-level driver programs developed for MCU.
• External framework for RTOS real-time operating systems (used as a driver device framework).
• Rapid development of various IoT and smart hardware products.

Driver Device Framework

Developers can access peripherals in an object-oriented manner, simplifying the development process of driver logic. The framework implements generic driver templates for commonly used peripherals, allowing developers to quickly port them to different hardware platforms.

The driver device framework supports generic interfaces for ordinary devices, automatic bus control for bus devices, and interrupt takeover for various devices.

Driver Device Interface

The device driver framework provides a unified operation interface, and all operations on devices need to be implemented through the following interfaces:

Example of Using SPI Device:

/* Define SPI device */
#define SPI_DEVICE0_CS_PIN              10
#define SPI_DEVICE1_CS_PIN              20
struct mr_spi_device spi_device0, spi_device1;

/* Add SPI device */
mr_spi_device_add(&spi_device0, "spi10", SPI_DEVICE0_CS_PIN);
mr_spi_device_add(&spi_device1, "spi11", SPI_DEVICE1_CS_PIN);

/* Find SPI device */
mr_device_t spi0_device = mr_device_find("spi10");
mr_device_t spi1_device = mr_device_find("spi11");

/* Mount bus */
mr_device_ioctl(spi0_device, MR_CTRL_ATTACH, "spi1");
mr_device_ioctl(spi1_device, MR_CTRL_ATTACH, "spi1");

/* Open SPI device in read-write mode */
mr_device_open(spi0_device, MR_OPEN_RDWR);
mr_device_open(spi1_device, MR_OPEN_RDWR);

/* Send data */
char buffer0[] = "hello";
char buffer1[] = "world";
mr_device_write(spi0_device, 0, buffer0, sizeof(buffer0) - 1);
mr_device_write(spi1_device, 0, buffer1, sizeof(buffer1) - 1);

/* Read data */
mr_device_read(spi0_device, 0, buffer0, sizeof(buffer0) - 1);
mr_device_read(spi1_device, 0, buffer1, sizeof(buffer1) - 1);

/* Close device */
mr_device_close(spi0_device);
mr_device_close(spi1_device);

Service Framework

The mr-library framework integrates a lightweight service framework for building application services in embedded development, supporting asynchronous event listening, multi-timer software timers, etc. It decouples different applications at the application layer through the service framework, achieving modularity, cuttable design, clear business logic, rapid development, and high code reuse.

Event Service

Event service is an asynchronous event processing mechanism that can effectively improve the system’s asynchronous processing capability, decoupling, and scalability through event dispatching and callbacks.

The event service consists of two parts: the event server and events.

• The event server is used to receive and dispatch events, maintaining an event queue for storing pending events and an event list for storing created events.
• Events need to be created on the event server and provide a callback function.

When an event occurs, the event server inserts the event into the event queue for buffering. The event server periodically retrieves events from the event queue for dispatching and finds the corresponding event callback for event processing.

Event Service Operation Interface

Example of Using Event Service:

/* Define events */
#define EVENT1                          1
#define EVENT2                          2
#define EVENT3                          3

/* Define event server */
struct mr_event_server event_server;

mr_err_t event1_cb(mr_event_server_t server, void *args)
{
    printf("event1_cb\r\n");
    
    /* Notify event server that event2 occurred */
    mr_event_notify(EVENT2, server);
    return MR_ERR_OK;
}

mr_err_t event2_cb(mr_event_server_t server, void *args)
{
    printf("event2_cb\r\n");

    /* Notify event server that event3 occurred */
    mr_event_notify(EVENT3, server);
    return MR_ERR_OK;
}

mr_err_t event3_cb(mr_event_server_t server, void *args)
{
    printf("event3_cb\r\n");
    return MR_ERR_OK;
}

int main(void)
{
    /* Add event server to kernel container */
    mr_event_server_add(&event_server, "server", 4);
    
    /* Create events on the server */
    mr_event_create(EVENT1, event1_cb, MR_NULL, &event_server);
    mr_event_create(EVENT2, event2_cb, MR_NULL, &event_server);
    mr_event_create(EVENT3, event3_cb, MR_NULL, &event_server);
    
    /* Notify event server that event1 occurred */
    mr_event_notify(EVENT1, &event_server);
    
    while (1)
    {
        /* Event server processing */
        mr_event_server_handle(&event_server);
    }
}

Phenomenon:

event1_cb
event2_cb
event3_cb

Software Timer Service

The software timer is a mechanism that implements timing functions at the software level. With software timers, specific events can be triggered at specific points in time or after certain intervals. Software timers are commonly used for implementing periodic tasks, timeout handling, timer interrupts, etc.

The software timer consists of two main components: the timer server and the timer.

• The timer server is used for time management and timer processing.
• The timer is used for handling specific timeout processing, and it needs to be registered with the timer server and provide a callback function.

Software Timer Service Operation Interface

Example of Using Software Timer Service:

/* Define timer server and timers */
struct mr_soft_timer_server server;
struct mr_soft_timer timer1, timer2, timer3;

mr_err_t timer1_callback(mr_soft_timer timer, void *args)
{
    printf("timer1_callback\r\n");
    return MR_ERR_OK;
}

mr_err_t timer2_callback(mr_soft_timer timer, void *args)
{
    printf("timer2_callback\r\n");
    return MR_ERR_OK;
}

mr_err_t timer3_callback(mr_soft_timer timer, void *args)
{
    printf("timer3_callback\r\n");
    mr_soft_timer_stop(timer);
    return MR_ERR_OK;
}

int main(void)
{
    /* Add timer server */
    mr_soft_timer_server_add(&server, "soft-timer");

    /* Add timers and start */
    mr_soft_timer_add_then_start(&timer1, 5, timer1_callback, MR_NULL, &server);
    mr_soft_timer_add_then_start(&timer2, 10, timer2_callback, MR_NULL, &server);
    mr_soft_timer_add_then_start(&timer3, 15, timer3_callback, MR_NULL, &server);

    while (1)
    {
        /* Update timer server clock */
        mr_soft_timer_server_update(&server, 1);
        
        /* Timer server processing (where the callback will be called) */
        mr_soft_timer_server_handle(&server);
    }
}

Code Directory

The code directory structure of mr-library is shown in the table below:

• Kernel Layer: The core part of mr-library, implementing object management, device control, service interfaces, etc.
• Device Layer: Provides a unified device interface to connect devices to the kernel.
• Driver Layer: Provides low-level hardware drivers for devices, requiring only modifications to the driver layer when hardware changes.
• Component Layer: Implements different functionalities through APIs provided by the framework, including but not limited to virtual file systems, generic sensor modules, network frameworks, etc.
• Software Packages: Standalone packages with no dependencies.