129 lines
1.8 KiB
NASM
129 lines
1.8 KiB
NASM
CPU 8086
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ORG 0x500
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jmp start
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;Interrupt handler
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;Return to the shell
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int0x20:
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jmp shell
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;Input and output
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int0x21:
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cmp ah, 0x0
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je printstr
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cmp ah, 0x1
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je readstr
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cmp ah, 0x2
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je println
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cmp ah, 0x3
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je readln
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iret
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;Disk operations
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int0x22:
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cmp ah, 0x0
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je loadf
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;To do: savef
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iret
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;System calls
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%include "PRINTSTR.INC"
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%include "READSTR.INC"
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%include "PRINTLN.INC"
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%include "READLN.INC"
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%include "LOADF.INC"
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start:
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;Set up the interrupt vectors
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;Interrupt 0x20 offset
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mov ax, int0x20
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mov [0x80], ax
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;Interrupt 0x21 offset
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mov ax, int0x21
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mov [0x84], ax
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;Interrupt 0x22 offset
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mov ax, int0x22
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mov [0x88], ax
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;Segments
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mov ax, 0x0
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mov [0x82], ax
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mov [0x86], ax
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mov [0x8a], ax
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;Store the boot drive number
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mov [drive], dl
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;Print a welcome message
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mov si, welcomemsg
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mov ah, 0x2
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int 0x21
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shell:
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;Re-set the stack
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cli
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mov sp, 0x0
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sti
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;Prompt for and read a command
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;Print a prompt
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mov si, prompt
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mov ah, 0x0
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int 0x21
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;Read
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mov di, input
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mov al, 0x4e
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mov ah, 0x3
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int 0x21
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;Load an execute the program
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;Check for an empty command
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cmp byte [input], 0x0
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jz shell
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;Load
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mov bx, 0x2000
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mov si, input
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mov ah, 0x0
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int 0x22
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;Check for errors
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cmp al, 0x1
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je error
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;Execute
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jmp 0x2000
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;Print an error message and return to the shell
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error:
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mov bh, 0x0
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mov ah, 0x3
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int 0x10
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dec dh
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mov ah, 0x2
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int 0x10
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mov si, errormsg
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mov ah, 0x2
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int 0x21
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jmp shell
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;Data
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drive db 0x0
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welcomemsg db 0xd, 0xa, "Welcome to EttinOS!", 0xd, 0xa, 0x0
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prompt db "> ", 0x0
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errormsg db "Unknown command", 0x0
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input times 0x4e db 0x0
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crlf db 0xd, 0xa, 0x0
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;Print a CRLF
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printcrlf:
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;Store the initial registers in the stack
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push si
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;Print the CRLF
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mov si, crlf
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mov ah, 0x0
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int 0x21
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;Load the initial registers from the stack
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pop si
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ret
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;File system buffer
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buffer:
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