Minix1.5/kernel/type.h

struct tasktab {
  void (*initial_pc)();
  int stksize;
  char name[8];
};

#if (CHIP == INTEL || CHIP == M68000)

/* The u.._t types and their derivatives are used when the precise size
 * must be specified for some reason, e.g., to match descriptor table
 * layouts.
 */
typedef unsigned char u8_t;	/* unsigned 8 bits */
typedef unsigned short u16_t;	/* unsigned 16 bits */
typedef unsigned long u32_t;	/* unsigned 32 bits */

#endif

#if (CHIP == INTEL)

/* The register type is usually the natural 'unsigned', but not during 386
 * initialization, when it has to be unsigned long!
 */
#if INTEL_32BITS
typedef u32_t reg_t;		/* machine register */
#else
typedef u16_t reg_t;
#endif

/* The stack frame layout is determined by the software, but for efficiency
 * it is laid out so the assembly code to use it is as simple as possible.
 * 80286 protected mode and all real modes use the same frame, built with
 * 16-bit registers.  Real mode lacks an automatic stack switch, so little
 * is lost by using the 286 frame for it.  The 386 frame differs only in
 * having 32-bit registers and more segment registers.  The same names are
 * used for the larger registers to avoid differences in the code.
 */
struct stackframe_s {
#if INTEL_32BITS
  u16_t gs;
  u16_t fs;
#endif
  u16_t es;
  u16_t ds;
  reg_t di;			/* di through cx are not accessed in C */
  reg_t si;			/* order is to match pusha/popa */
  reg_t bp;
  reg_t st;			/* hole for another copy of sp */
  reg_t bx;
  reg_t dx;
  reg_t cx;
  reg_t retreg;			/* ax */
  reg_t retadr;			/* return address for assembly code save() */
  reg_t pc;			/* interrupt pushes rest of frame */
  reg_t cs;
  reg_t psw;
  reg_t sp;
  reg_t ss;
};

struct segdesc_s {		/* segment descriptor for protected mode */
  u16_t limit_low;
  u16_t base_low;
  u8_t base_middle;
  u8_t access;			/* |P|DL|1|X|E|R|A| */
#if INTEL_32BITS
  u8_t granularity;		/* |G|X|0|A|LIMT| */
  u8_t base_high;
#else
  u16_t reserved;
#endif
};

struct farptr_s {		/* far pointer for debugger hooks */
  reg_t offset;
  u16_t selector;
#if INTEL_32BITS
  u16_t pad;
#endif
};

#endif /* (CHIP == INTEL) */

#if (CHIP == M68000)
typedef u32_t reg_t;		/* machine register */

/* the name of the following struct and some of the fields are
   chosen for PC compatibility */
struct stackframe_s {
  reg_t retreg;			/* d0 */
  reg_t d1;
  reg_t d2;
  reg_t d3;
  reg_t d4;
  reg_t d5;
  reg_t d6;
  reg_t d7;
  reg_t a0;
  reg_t a1;
  reg_t a2;
  reg_t a3;
  reg_t a4;
  reg_t a5;
  reg_t a6;
  reg_t sp;			/* also known as a7 */
  reg_t pc;
  u16_t psw;
  u16_t dummy;			/* make size multiple of reg_t for system.c */
};
#endif /* (CHIP == M68000) */