47 lines
1.8 KiB
NASM
47 lines
1.8 KiB
NASM
; Set up the interrupt descriptor table
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; This is to be stored at 0x0000:0x0000
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%macro m_setup_idt 0
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push es
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push di
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xor ax, ax
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mov es, ax
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mov di, 0x0000
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mov cx, 2048 ; Write 2048 byte of zero so now into the IDT
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cld
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rep stosb
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%endmacro
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; Set up the global descriptor table
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; This is to be stored at 0x0000:0x0800
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%macro m_setup_gdt 0
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; NULL Descriptor:
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mov cx, 4 ; Write the NULL descriptor,
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rep stosw ; which is 4 zero-words.
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; Code segment descriptor:
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mov [es:di], word 0xFFFF ; limit = 0xFFFF (since granularity bit is set, this is 4 GB)
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mov [es:di + 2], word 0x0000 ; base = 0x0000
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mov [es:di + 4], byte 0x00 ; base
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mov [es:di + 5], byte 0x9A ; access = 1001 1010; segment present, ring 0, S=code/data, type=0xA (code, execute/read)
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mov [es:di + 6], byte 0xCF ; granularity = 1100 1111; limit = 0xf, AVL=0, L=0, 32bit, G=1
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mov [es:di + 7], byte 0x00 ; base
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add di, 8
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; Data segment descriptor:
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mov [es:di], word 0xFFFF ; limit = 0xFFFF (since granularity bit is set, this is 4 GB)
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mov [es:di + 2], word 0x0000 ; base = 0x0000
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mov [es:di + 4], byte 0x00 ; base
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mov [es:di + 5], byte 0x92 ; access = 1001 0010; segment present, ring 0, S=code/data, type=0x2 (data, read/write)
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mov [es:di + 6], byte 0xCF ; granularity = 1100 1111; limit = 0xf, AVL=0, L=0, 32bit, G=1
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mov [es:di + 7], byte 0x00 ; base
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pop di
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pop es
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%endmacro
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; Tell the CPU of the GDT and IDT
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%macro m_load_gdt_and_idt 0
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cli
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lgdt [gdt_descriptor]
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lidt [idt_descriptor]
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%endmacro
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