Architettura software integrata - Qual è la differenza tra DAL e HAL?

Mi piacerebbe sapere qual è la differenza tra HAL (Hardware Abstraction Layer) e DAL (Data Abstraction Layer) quando parliamo di software embedded. Potrei avere le abbreviazioni sbagliate però ...

La mia comprensione è che al livello HAL si usano i registri di mcu mentre al livello DAL non si. Ho scritto un rapido esempio di come implementare personalmente un driver UART a livello HAL e DAL:

/***************************************************************************************************************************
 * HAL
 ***************************************************************************************************************************/


#define UART_PARITY (*((volatile unsigned long *) 0x0000123))
#define T0IR        (*((volatile unsigned long *) 0x0000124))
#define U0THR       (*((volatile unsigned long *) 0x0000125))
#define UART_BDR    (*((volatile unsigned long *) 0x0000126))

typedef enum{
    UART_HAL_STATUS_SUCCESS,
    UART_HAL_STATUS_ERROR
} uart_hal_status_t;

typedef struct{

} uart_hal_t;

/* Write some values to registers. */
uart_hal_status_t UART_HAL_init(p_baudrate, p_parity, p_device)
{
    /* Calculates which exact value needs to be written to register to have desired baudrate. */
    unsigned long x = ((p_baudrate/2)*PLL*SMTH);
    UART_BDR = x;

    /* Write values to registers. */
    if (p_parity == 0)
    {
        UART_PARITY = 1<<8;
    }
    else
    {
        UART_PARITY = 0<<8;
    }

    /* Set some additional register values. */
    VICSoftIntClr = 0x20;
    T0IR =0xFF;
    VICVectAddr =0x00000000;

    return UART_HAL_STATUS_SUCCESS;
}

uart_hal_status_t UART_HAL_read_char(uart_hal_t p_uart_dev)
{
    //read registers
}

/***************************************************************************************************************************
 * DAL
 ***************************************************************************************************************************/

#include <uarth_hal.h>
#include <inttypes.h>

/**
 * Parity types.
 */
typedef enum{
    PARITY_ODD,
    PARITY_EVEN
} parity_t;

/**
 *  Return values.
 */
typedef enum{
    UART_DAL_STATUS_SUCCESS,
    UART_DAL_STATUS_ERROR
}uart_dal_status_t;

/**
 * Physical UART devices.
 */
typedef enum{
    UART_DEV_0,
    UART_DEV_1,
    UART_DEV_2
} uart_dev_t;


/**
 * Publicly accessible configuration structure.
 */
typedef struct{
    int32_t baudrate;
    parity_t parity;

    uart_dev_t device;
} UART_cfg_t;

/**
 * Wannabe opaque structure.
 */
typedef struct{
    UART_cfg_t config;

    uart_hal_t hal_device; 

    void *rx_buffer;
    uint32_t rx_buffer_nr_unread_chars;
    uint32_t rx_buffer_size;
} UART_t;

/**
 * This function initializes the UART port at the DAL level
 */
uart_dal_status_t UART_DAL_init(UART_t *p_uart_dev, UART_cfg_t *p_uart_cfg)
{
    if ((p_uart_dev == NULL) || (p_uart_cfg == NULL))
    {
        return UART_DAL_STATUS_ERROR;
    }

    UART_HAL_init(p_uart_cfg->baudrate, p_uart_cfg->parity, p_uart_cfg->device);

    p_uart_dev->config = *(p_uart_cfg);

    return UART_DAL_STATUS_SUCCESS;
}

uart_dal_status_t UART_DAL_read_data(UART_t *p_uart_dev)
{
    for (uint32_t i = 0; i < p_uart_dev->rx_buffer_nr_unread_chars; i++)
    {
        UART_HAL_read_char(p_uart_dev->hal_device);
    }

    return UART_DAL_STATUS_SUCCESS;
}

/***************************************************************************************************************************
 * main
 ***************************************************************************************************************************/

#include <uart_dal.h>

int main (int p_argc, char *p_argv[])
{
    UART_t l_uart_dev;

    UART_cfg_t l_uart_cfg = 
    {
        .baudrate = 9600,
        .parity = PARITY_ODD,
        .device = UART_DEV_0
    };

    uart_dal_status_t l_status = UART_DAL_init(&l_uart_dev, &l_uart_cfg);
    if (l_status != UART_DAL_STATUS_SUCCESS)
    {
        return -1;
    }

    while(1);

    return 0;
}

Per chiarire, ho creato tutti quei valori e i nomi dei registri.