;============================================================================= ; kernel.asm - Example operating system kernel. ; ; Copyright (C) 1992-93, Dennis Marer File created: 12/21/92 ; Last modified: 1/27/93 ; ; Description: ; This file represents the kernel of some fictional operating system. At ; this point, it supplies only basic functionality, just as an example of ; the 386 Protected Mode and 32-bit code segments. ; ; Portability: ; Requires Turbo Assembler 1.0 (TASM) or better to be assembled. ; Dependent on the IBM PC 386 or better platform and its standard devices. ; ; Modifications: ; DPM, 1/27/93 Finished the first revision of this file. ;============================================================================= .386p include kernel.inc include 386p.inc ; 386 Protected mode include ibmpc.inc ; IBM PC hardware ;============================ Kernel data segment ============================ KernelData segment para use32 'KernelData' ;----------------------------------------------------------------------------- ; Messages and general data. ;----------------------------------------------------------------------------- msgDivide db 'Divide error, system halted.',13,0 msgNMI db 'NMI, system halted.',13,0 msgOverflow db 'Overflow error, system halted.',13,0 msgBounds db 'Bound error, system halted.',13,0 msgOpcode db 'Opcode error, system halted.',13,0 msgMathGone db 'Math coprocessor gone error, system halted.',13,0 msgDouble db 'Double fault error, system halted.',13,0 msgMathOver db 'Math coprocessor overrun error, system halted.',13,0 msgTSS db 'Invalid TSS error, system halted.',13,0 msgSegment db 'Segment present error, system halted.',13,0 msgStack db 'Stack fault error, system halted.',13,0 msgGeneral db 'General protection error, system halted.',13,0 msgPage db 'Page fault error, system halted.',13,0 msgMathErr db 'Math coprocessor error, system halted.',13,0 kernelMsg db 'Welcome to 80386 Protected Mode!',13,0 intrMsg db 'This is generated by the 8253 timer interrupt: ',0 statusMsg db 'This is generated by an infinite loop: ',0 megMsg db 'Memory above 1 megabyte has been accessed!',13,0 hex db '0x',0 clock dd 0 cursorX dw 0 cursorY dw 0 ;----------------------------------------------------------------------------- ; Stacks. ;----------------------------------------------------------------------------- align 16 dw 256 dup (?) stackI equ $ dw 256 dup (?) stack0 equ $ dw 128 dup (?) stack1 equ $ dw 128 dup (?) stack2 equ $ dw 256 dup (?) ; This is the initial (level stack3 equ $ ; 3) VM stack initStack label dword ; Initial PM stack dw stackI dw KernelData KernelData ends ;========================= Basic Display functions =========================== Kernel segment para use32 'Kernel' assume CS:Kernel,DS:KernelData ;----------------------------------------------------------------------------- ; ClearScreen - Clear the screen, reset the cursor location. ; ; No registers modified. ;----------------------------------------------------------------------------- ClearScreen proc near push AX ; Store the used registers push CX push EDI push ES mov AX,selScreen ; Put the screen segment mov ES,AX ; into ES mov CX,80*25 ; Get ready to clear each mov AX,0700h ; character on the screen xor EDI,EDI rep stosw mov AX,selKDS ; Put the data segment mov ES,AX ; into ES mov ES:cursorX,0 ; Reset the cursor location mov ES:cursorY,0 ; back to the origin pop ES ; Restore the used registers pop EDI pop CX pop AX ret ClearScreen endp ;----------------------------------------------------------------------------- ; OutChar - Output a character to the screen, and update the cursor location. ; ; Parameters: ; AL - The character to be output. ; ; No registers modified. ;----------------------------------------------------------------------------- OutChar proc near push AX ; Store the used registers push BX push CX push EDI push DS push ES push AX mov AX,selKDS ; Put the data segment mov DS,AX ; into FS mov AX,selScreen ; Put the screen segment mov ES,AX ; into ES mov BX,cursorY ; Load the current cursor mov CX,cursorX ; position into CX,BX mov AL,80 ; Calculate the address of mul BL ; the character and place add AX,CX ; this into EDI movzx EDI,AX shl EDI,1 pop AX ; Get the character cmp AL,13 ; New line character? je OutcharLine mov AH,07h ; Add character attributes mov ES:[EDI],AX ; Write character to screen inc CX ; Increment the X location cmp CX,80 ; If the line length has been je OutcharLine ; exceeded, go to next mov cursorX,CX ; Store line X location jmp OutcharDone OutcharLine: inc BX ; Increment the cursor Y mov cursorX,0 ; location and clear the mov cursorY,BX ; X location OutcharDone: pop ES ; Restore the used registers pop DS pop EDI pop CX pop BX pop AX ret Outchar endp ;---------------------------------------------------------------------------- ; Message - Write a message to the screen at the current cursor location. ; The cursor location is updated to the last character of the message; ; ; Parameters: ; DS:ESI - A pointer to the null-terminated message to be displayed. ; ; Registers modified: ; None. ;----------------------------------------------------------------------------- Message proc near push AX ; Store the used registers push ESI xor AH,AH ; Clear AH for comparisons MessageLoop: lodsb ; Load a character cmp AL,AH ; See if its the NULL char, je MessageDone ; through if found call Outchar ; Output the character jmp MessageLoop MessageDone: pop ESI ; Restore the used registers pop AX ret Message endp ;----------------------------------------------------------------------------- ; Hexout - Output the 16-bit number stored in AX in hexidecimal format. ; ; Parameters: ; AX - The 16-bit value to be output. ; ; No registers modified. ;----------------------------------------------------------------------------- Hexout proc near push AX ; Store the used registers push BX push ECX mov BX,selKDS ; Output the string '0x' to mov DS,BX ; indicate a hexidecimal mov ESI,offset hex ; number is printed call Message mov BX,AX ; Copy the 16-bit value mov ECX,4 ; Set count to 4 digits HexoutLoop: rol BX,4 ; Put next digit into view mov AL,BL ; Copy into AL, then mask and AL,0Fh ; out all but 4 bits cmp AL,9 ; If it's a decimal number jle HexoutDec ; jump ahead add AL,'A'-'9'-1 ; Compensate for alphabet HexoutDec: add AL,'0' ; Convert into ASCII call Outchar ; Output the character loop HexoutLoop pop ECX ; Restore the used registers pop BX pop AX ret Hexout endp ;----------------------------------------------------------------------------- ; HexoutL - Output the 32-bit number stored in EAX in hexidecimal format. ; ; Parameters: ; EAX - The 32-bit value to be output. ; ; No registers modified. ;----------------------------------------------------------------------------- HexoutL proc near push EAX ; Store the used registers push EBX push ECX push DS mov BX,selKDS ; Output the string '0x' to mov DS,BX ; indicate a hexidecimal mov ESI,offset hex ; number is printed call Message mov EBX,EAX ; Copy the 32-bit value mov ECX,8 ; Set count to 8 digits HexoutLLoop: rol EBX,4 ; Put next digit into view mov AL,BL ; Copy into AL, then mask and AL,0Fh ; out all but 4 bits cmp AL,9 ; If it's a decimal number jle HexoutLDec ; jump ahead add AL,'A'-'9'-1 ; Compensate for alphabet HexoutLDec: add AL,'0' ; Convert into ASCII call Outchar ; Output the character loop HexoutLLoop pop DS ; Restore the used registers pop ECX pop EBX pop EAX ret HexoutL endp ;============================ Interrupt Handlers ============================= ;----------------------------------------------------------------------------- ; IntrDivide - Divide error (interrupt 0) handler. ;----------------------------------------------------------------------------- IntrDivide: mov ESI,offset msgDivide jmp Abort ;----------------------------------------------------------------------------- ; IntrDebug - Debug exception (interrupt 1) handler. ;----------------------------------------------------------------------------- IntrDebug: iretd ;----------------------------------------------------------------------------- ; IntrNMI - Non-Maskable Interrupt (interrupt 2) handler. ;----------------------------------------------------------------------------- IntrNMI: jmp Abort ;----------------------------------------------------------------------------- ; IntrBreakpoint - One byte interrupt (interrupt 3) handler. ;----------------------------------------------------------------------------- IntrBreakpoint: iretd ;----------------------------------------------------------------------------- ; IntrOverflow - Interrupt on overflow (interrupt 4) handler. ;----------------------------------------------------------------------------- IntrOverflow: mov ESI,offset msgOverflow jmp Abort ;----------------------------------------------------------------------------- ; IntrBounds - Array bounds check (interrupt 5) handler. ;----------------------------------------------------------------------------- IntrBounds: mov ESI,offset msgBounds jmp Abort ;----------------------------------------------------------------------------- ; IntrOpcode - Illegal opcode (interrupt 6) handler. ;----------------------------------------------------------------------------- IntrOpcode: mov ESI,offset msgOpcode jmp Abort ;----------------------------------------------------------------------------- ; IntrMathGone - Math coprocessor device not available (interrupt 7) handler. ;----------------------------------------------------------------------------- IntrMathGone: mov ESI,offset msgMathGone jmp Abort ;----------------------------------------------------------------------------- ; IntrDouble - Double fault (interrupt 8) handler. ;----------------------------------------------------------------------------- IntrDouble: mov ESI,offset msgDouble jmp Abort ;----------------------------------------------------------------------------- ; IntrMathOver - Math coprocessor segment overrun (interrupt 9) handler. ;----------------------------------------------------------------------------- IntrMathOver: mov ESI,offset msgMathOver jmp Abort ;----------------------------------------------------------------------------- ; IntrTSS - Illegal TSS (interrupt 10) handler. ;----------------------------------------------------------------------------- IntrTSS: mov ESI,offset msgTSS jmp Abort ;----------------------------------------------------------------------------- ; IntrSegment - Segment not present (interrupt 11) handler. ;----------------------------------------------------------------------------- IntrSegment: mov ESI,offset msgSegment jmp Abort ;----------------------------------------------------------------------------- ; IntrStack - Stack fault (interrupt 12) handler. ;----------------------------------------------------------------------------- IntrStack: mov ESI,offset msgStack jmp Abort ;----------------------------------------------------------------------------- ; IntrGeneral - General protection (interrupt 13) handler. ;----------------------------------------------------------------------------- IntrGeneral: mov ESI,offset msgGeneral jmp Abort ;----------------------------------------------------------------------------- ; IntrPage - Page fault (interrupt 14) handler. ;----------------------------------------------------------------------------- IntrPage: mov ESI,offset msgPage jmp Abort ;----------------------------------------------------------------------------- ; IntrMathErr - Math coprocessor error (interrupt 16) handler. ;----------------------------------------------------------------------------- IntrMathErr: mov ESI,offset msgMathErr jmp Abort ;----------------------------------------------------------------------------- ; KernelClock - Kernel system clock interrupt (IRQ 0) handler. ;----------------------------------------------------------------------------- KernelClock: push EAX ; Store the used registers push BX push CX push ESI push DS push ES mov AX,selKDS ; Load the data segment mov DS,AX mov BX,cursorX ; Save the cursor location mov CX,cursorY mov cursorX,0 ; Set a new location mov cursorY,12 mov ESI,offset intrMsg ; Print interrupt message call Message mov EAX,clock ; Load the clock count inc EAX ; Increment the clock count mov clock,EAX ; and save it for later call HexoutL ; Output the clock count mov cursorX,BX ; Restore the cursor location mov cursorY,CX mov AL,PIC_EOI ; Signal to the PIC that the out PIC1_CMND,AL ; interrupt was serviced pop ES ; Restore the used registers pop DS pop ESI pop CX pop BX pop EAX iretd ;----------------------------------------------------------------------------- ; Reserved - Intel reserved interrupt (interrupt 15, 17-32) handler. Do ; nothing except notify both PICs the interrupt has been serviced. ;----------------------------------------------------------------------------- Reserved: push AX ; Store the used registers mov AL,PIC_EOI ; Signal both the slave and out PIC1_CMND,AL ; master PIC the interrupt out PIC2_CMND,AL ; has been serviced pop AX ; Restore the used registers iretd ;----------------------------------------------------------------------------- ; Unused - Unused vector interrupt handler. Do nothing except notify both ; PICs the interrupt has been serviced. ;----------------------------------------------------------------------------- Unused: push AX ; Store the used registers mov AL,PIC_EOI ; Signal both the slave and out PIC1_CMND,AL ; master PIC the interrupt out PIC2_CMND,AL ; has been serviced pop AX ; Restore the used registers iretd ;----------------------------------------------------------------------------- ; Abort - One of the fault handlers has been called, print a message then ; jump into an infinite loop. ;----------------------------------------------------------------------------- Abort: mov AX,selKDS mov DS,AX call Message AbortLoop: jmp AbortLoop ;=========================== Kernel Initialization =========================== ;----------------------------------------------------------------------------- ; Start up the kernel, load the stack and data segments, insure ESP is going ; to be 32-bits, perform a few tests, print a few messages, then go into ; an infinite loop to indicate we're running in protected mode. ;----------------------------------------------------------------------------- KernelStart: movzx ESP,SP ; Ensure that ESP is 32-bits mov AX,selKDS ; Set up initial DS and SS mov SS,AX mov AX,selKDS mov DS,AX mov AX,selKernel ; Set the current TSS ltr AX mov AX,selKDS ; Set all selectors to mov ES,AX ; a valid value mov FS,AX mov GS,AX call ClearScreen ; Clear the screen sti ; Enable interrupts mov ESI,offset kernelMsg ; Print a welcome message call Message mov AX,sel1Meg ; Even though this doesn't mov ES,AX ; prove anything, access xor EBX,EBX ; memory above 1 megabyte mov EAX,ES:[EBX] mov ESI,offset megMsg ; Print 1 meg success message call Message mov ESI,offset statusMsg ; Display a status message mov cursorX,0 ; Set a good cursor location mov cursorY,10 call Message xor EAX,EAX ; Clear the counter KernelLoop: mov cursorX,39 ; Set a good cursor location mov cursorY,10 call HexoutL ; Display counter hex value inc EAX ; Increment the counter and jmp KernelLoop ; loop infinitely Kernel ends end