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Use a low address to store GDT and E820 #20

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6 changes: 4 additions & 2 deletions bsp/x86/bootsector.s
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,7 @@

CYLS = 10
BOOTSEG = 0x07C0
INITSEG = 0x7000
INITSEG = 0x0050

@coolgw coolgw Feb 13, 2020

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use #include <common.h> and remove INITSEG here.
BTW: the file name bootsector.s to bootsector.S.

SYSSEG = 0x1000
.code16
.section ".bstext", "ax"
Expand All @@ -21,7 +21,7 @@ main_start:
xorw %sp, %sp


#move BootSector to 0x9000(INITSEG)
#move BootSector to INITSEG
#
movw $BOOTSEG, %ax
movw %ax, %ds
Expand Down Expand Up @@ -181,6 +181,8 @@ fin:
mov $0x13,%al
int $0x10
#
#Jump into INITSEG, rather than SYSSEG, because
#We want to store e820 at $INITSEG:$E820_OFFSET. Our SYSSEG(0x1000) as real start
ljmp $INITSEG, $lowlevel_init
hlt

Expand Down
9 changes: 4 additions & 5 deletions bsp/x86/lowlevel_init.s
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Expand Up @@ -81,7 +81,7 @@ _lowlevel_init:
nop;
nop;

#Get memory map and store memroy table start from 0x00098004, each entry has 20bytes data but
#Get memory map and store memroy table start from $INITSEG:1004, each entry has 20bytes data but
#currently we reserve 0x20 bytes for each entry
#Each entry has :
#First uint64_t = Base address
Expand All @@ -93,7 +93,8 @@ _lowlevel_init:
# Type 4: ACPI NVS memory
# Type 5: Area containing bad memory
#Set register base https://wiki.osdev.org/Detecting_Memory_(x86)
mov $0x8004, %di
E820_OFFSET=0x1004

@coolgw coolgw Feb 13, 2020

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same comment, move E820_OFFSET to common.h

mov $E820_OFFSET, %di
xor %ebx, %ebx
mov $0x0534D4150, %edx
mov $0xe820,%eax
Expand All @@ -107,8 +108,6 @@ get_next:
int $0x15
cmp $0, %ebx /*ebx=0 means no other entry*/
jnz get_next
#for debug
# hlt

#Inital Serial Device 1
#com1 at 0x3F8
Expand Down Expand Up @@ -185,7 +184,7 @@ fin:
hlt
jmp fin

INITSEG = 0x7000
INITSEG = 0x0050

@coolgw coolgw Feb 13, 2020

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same as above


idt_ptr:
.word 0 /* limit */
Expand Down
4 changes: 3 additions & 1 deletion include/common.h
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Expand Up @@ -25,6 +25,7 @@ extern struct bitmap_font font;
unsigned int memtest(unsigned int start, unsigned int end);

#define SYSSEG 0x1000
#define INITSEG 0x0050
#define MEMMAN_ADDR (char *)((0x003c0000) - (SYSSEG << 4))
#define VRAM_ADDR (unsigned char *)((0xa0000)-(SYSSEG << 4))
#define COL8_000000 0
Expand All @@ -43,7 +44,8 @@ unsigned int memtest(unsigned int start, unsigned int end);
#define COL8_840084 13
#define COL8_008484 14
#define COL8_848484 15
#define MEM_MAP_ADDR (char *)((0x00078004)-(SYSSEG << 4))
#define E820_OFFSET 0x1004
#define MEM_MAP_ADDR (char *)((INITSEG << 4)+(E820_OFFSET)-(SYSSEG << 4))

@coolgw coolgw Feb 13, 2020

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I suppose this is the address after paging? so this PR depend on the paging PR?


struct SEGMENT_DESCRIPTOR {
short limit_low, base_low;
Expand Down