《30天自制操作系统总结》

    struct FREEINFO {	/* information */
    	unsigned int addr, size;
    };
    struct MEMMAN {		/* Memory management */
    	int frees, maxfrees, lostsize, losts;
    	struct FREEINFO free[MEMMAN_FREES];  	//MEMMAN_FREE=4090
    };

    struct TSS32 {
    	int backlink, esp0, ss0, esp1, ss1, esp2, ss2, cr3;
    	// eip-程序计数器，指向当前执行代码位置，设置为任务代码的起始地址
    	// esp - 指向栈顶
    	int eip, eflags, eax, ecx, edx, ebx, esp, ebp, esi, edi;
    	// cs-代码所在的段号
    	int es, cs, ss, ds, fs, gs;
    	//ldtr ldt的选择符（指向GDT中的LDT描述符）
    	int ldtr, iomap;
    };

    struct TASK {
    	// sel-指向GDT中的TSS 
    	// flags: 0-未使用  1-sleep   2-running
    	int sel, flags; /* Sel is the number of GDT. */
    	// level-任务级别   priority*0.01s=分配的时间
    	int level, priority;
    	struct FIFO32 fifo;
    	struct TSS32 tss;
    	struct SEGMENT_DESCRIPTOR ldt[2];
    	struct CONSOLE *cons;
    	int ds_base, cons_stack;
    	struct FILEHANDLE *fhandle;
    	int *fat;
    	char *cmdline;
    };
    struct TASKLEVEL {
    	// 每个level 最多100个任务
    	int running; /* The number of tasks in operation */
    	int now; /* Variables that will let us know which task we're working on */
    	struct TASK *tasks[MAX_TASKS_LV];
    };
    struct TASKCTL {
    	// level0 优先级最高，最多10个level
    	int now_lv; /* At the operating level */
    	char lv_change; /*Do you want me to change levels next time with the taskup switch? */
    	struct TASKLEVEL level[MAX_TASKLEVELS];
    	struct TASK tasks0[MAX_TASKS];
    };

    struct FILEINFO {
    	// name[0]: 0xe5-此文件被删除  0x00-该段不包含文件信息
    	unsigned char name[8], ext[3], type;
    	char reserve[10];
    	// clusto-表示此文件从哪一个扇区开始存放
    	unsigned short time, date, clustno;
    	unsigned int size;
    };

    struct CONSOLE {
    	// sht: 对应图层  0-没有图层(ncst 命令用到)
    	struct SHEET *sht;
    	// x, y, c: 光标的位置、颜色
    	int cur_x, cur_y, cur_c;
    	// timer 用于光标闪烁的定时
    	struct TIMER *timer;
    };
    struct FILEHANDLE {
    	char *buf;
    	int size;
    	int pos;
    };

    q = (char *) memman_alloc_4k(memman, segsiz);
    task->ds_base = (int) q;
    set_segmdesc(task->ldt + 0, finfo->size - 1, (int) p, AR_CODE32_ER + 0x60); // p为代码起始地址
    set_segmdesc(task->ldt + 1, segsiz - 1,      (int) q, AR_DATA32_RW + 0x60);

    struct SHEET {
    	unsigned char *buf;
    	// flags: 0-未使用    1-使用中   (flags&0x10)!=0-该图层属于应用程序
    	// height:  -1-invisibility   max-top
    	// col_inv： 透明色色号
    	int bxsize, bysize, vx0, vy0, col_inv, height, flags; 
    	struct SHTCTL *ctl;
    	struct TASK *task;
    };
    struct SHTCTL {
    	unsigned char *vram, *map;
    	int xsize, ysize, top;
    	struct SHEET *sheets[MAX_SHEETS];
    	struct SHEET sheets0[MAX_SHEETS];
    };

    struct TIMER {
    	struct TIMER *next;
    	unsigned int timeout;
    	// flags: 0-未使用  1-已配置  2-使用中
    	// flags2: 0-一般定时器   1-应用程序申请定时器
    	char flags, flags2;
    	struct FIFO32 *fifo;
    	// 此定时器的标志数据
    	int data;
    };
    struct TIMERCTL {
    	// count 当前时间
    	// next 下一个timeout时间
    	// t0 当前计时器
    	unsigned int count, next;
    	struct TIMER *t0;
    	struct TIMER timers0[MAX_TIMER];
    };

    struct FIFO32 {
    	int *buf;
    	int p, q, size, free, flags;
    	struct TASK *task;  // 当有数据时需要被唤醒的任务
    };

      MOV         AL,0x13                 ; 3x200x8bit color VGA graphics

      MOV		AH,0x00
      INT		0x10
      MOV		BYTE [VMODE],8	; Note screen mode (see C language)
      MOV		WORD [SCRNX],320
      MOV		WORD [SCRNY],200
      MOV		DWORD [VRAM],0x000a0000