kern
view src/segm.c @ 40:710739e33da8
- now read_rtc doesn't try to read weekday as it's probably wrong anyway, and doesn't set yearday either
- mktime now fixes yearday and weekday
- moved init_timer and init_rtc just before enabling the interrupts in main
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Sun, 12 Jun 2011 15:45:21 +0300 |
| parents | 78d5c304ddd0 |
| children | 8ea6debe4265 |
line source
1 #include <string.h>
2 #include "segm.h"
3 #include "desc.h"
5 /* bits for the 3rd 16bt part of the descriptor */
6 #define BIT_ACCESSED (1 << 8)
7 #define BIT_WR (1 << 9)
8 #define BIT_RD (1 << 9)
9 #define BIT_EXP_DOWN (1 << 10)
10 #define BIT_CONFORMING (1 << 10)
11 #define BIT_CODE (1 << 11)
12 #define BIT_NOSYS (1 << 12)
13 #define BIT_PRESENT (1 << 15)
15 /* bits for the last 16bit part of the descriptor */
16 #define BIT_BIG (1 << 6)
17 #define BIT_DEFAULT (1 << 6)
18 #define BIT_GRAN (1 << 7)
20 enum {TYPE_DATA, TYPE_CODE};
22 static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);
24 /* these functions are implemented in segm-asm.S */
25 void setup_selectors(uint16_t code, uint16_t data);
26 void set_gdt(uint32_t addr, uint16_t limit);
29 /* our global descriptor table */
30 static desc_t gdt[3];
33 void init_segm(void)
34 {
35 memset(gdt, 0, sizeof gdt);
36 segm_desc(gdt + SEGM_KCODE, 0, 0xffffffff, 0, TYPE_CODE);
37 segm_desc(gdt + SEGM_KDATA, 0, 0xffffffff, 0, TYPE_DATA);
39 set_gdt((uint32_t)gdt, sizeof gdt - 1);
41 setup_selectors(selector(SEGM_KCODE, 0), selector(SEGM_KDATA, 0));
42 }
44 /* constructs a GDT selector based on index and priviledge level */
45 uint16_t selector(int idx, int rpl)
46 {
47 return (idx << 3) | (rpl & 3);
48 }
50 static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)
51 {
52 desc->d[0] = limit & 0xffff; /* low order 16bits of limit */
53 desc->d[1] = base & 0xffff; /* low order 16bits of base */
55 /* third 16bit part contains the last 8 bits of base, the 2 priviledge
56 * level bits starting on bit 13, present flag on bit 15, and type bits
57 * starting from bit 8
58 */
59 desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
60 BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));
62 /* last 16bit part contains the last nibble of limit, the last byte of
63 * base, and the granularity and deafult/big flags in bits 23 and 22 resp.
64 */
65 desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN | BIT_BIG;
66 }