/**
 * @file tss.h
 * @brief Task State Segment (TSS) definitions and structures
 * @author Jake Holtham
 * @date 2025
 * 
 * This header file contains the structure definitions for the x86 Task State Segment (TSS). 
*/

#ifndef TSS_H
#define TSS_H

#include <stdint.h>

/**
 * @brief Task State Segment structure
 * 
 * Data structure that contains information about a task,
 * including the state of the processor registers, stack pointers, and other task-specific
 * information. It is used by the x86 architecture for task switching and interrupt handling.
 * 
 * Packed to make sure it's aligned and the correct size.
 *
 * @note This structure must be aligned on a 4byte boundary
 */
typedef struct tss_s {
    uint32_t LINK;    /**< Previous TSS selector*/
    uint32_t ESP0;    /**< Stack pointer for privilege level0*/
    uint32_t SS0;     /**< Stack segment for privilege level0*/
    uint32_t ESP1;    /**< Stack pointer for privilege level1*/
    uint32_t SS1;     /**< Stack segment for privilege level1*/
    uint32_t ESP2;    /**< Stack pointer for privilege level2*/
    uint32_t SS2;     /**< Stack segment for privilege level2*/
    uint32_t CR3;     /**< Page Directory register */
    uint32_t EIP;     /**< Instruction pointer */
    uint32_t EFLAGS;  /**< Flags register */
    uint32_t EAX;     /**< General purpose */
    uint32_t ECX;     /**< General purpose */
    uint32_t EDX;     /**< General purpose */
    uint32_t EBX;     /**< General purpose */
    uint32_t ESP;     /**< Stack pointer */
    uint32_t ESI;     /**< Source index register */
    uint32_t EDI;     /**< Destination index register */
    uint32_t ES;      /**< Extra segment register */
    uint32_t CS;      /**< Code segment register */
    uint32_t SS;      /**< Stack segment register */
    uint32_t DS;      /**< Data segment register */
    uint32_t FS;      /**< Extra segment register FS */
    uint32_t GS;      /**< Extra segment register GS */
    uint32_t LDTR;    /**< Local descriptor table register */
    uint32_t IOPB;    /**< I/O permission bitmap offset */
    uint32_t SSP;     /**< Stack segment pointer */
} __attribute__((packed)) tss_t; 

/**
 * @brief Global TSS instance
 * 
 * This is the main TSS instance used by the kernel for task management.
 * It contains the current task's state information.
 * Defined in assembly.
 */
extern tss_t tss;

#endif /* TSS_H */