Makefile

@@ -1,8 +1,8 @@
 objects = entry.o kernel.o task.o handler.o interrupt.o v86.o print.o tss.o gdt.o\
 		  paging.o fault.o tests.o kbd.o helper.o disk.o file.o fs.o dosfs/dosfs.o fs_dos.o\
 		  progs.o hexedit.o textedit.o
-CFLAGS = -target "i386-elf" -m32 -mgeneral-regs-only -ffreestanding\
-		 -march=i386 -fno-stack-protector -Wno-int-conversion -nostdlib -c
+CFLAGS = -target "i686-elf" -m32 -mgeneral-regs-only -ffreestanding\
+		 -march=i686 -fno-stack-protector -Wno-int-conversion -nostdlib -c
 LFLAGS = -Wl,--gc-sections -Wl,--print-gc-sections -m32 -nostartfiles -nostdlib
 
 ifeq ($(OUTFILE),)

fault.nasm

@@ -70,13 +70,10 @@ jmp _fault_coda
 _gpf_old_ds: dw 0
 extern get_key
 extern get_scancode
-extern get_key_no_wait
-extern get_scancode_no_wait
 extern task_ptr
 extern _enter_v86_internal_no_task
 extern return_prev_task
 extern v86Interrupt
-extern TIMERVAL
 gpf_handler_32:
 push eax
 mov eax, dword [esp+8] ; EIP
@@ -94,24 +91,8 @@ jne .s1
 call get_key
 jmp .return_to_offender
 .s1: cmp al, 0x01 ; get scancode
-jne .s2
-call get_scancode
-jmp .return_to_offender
-.s2: cmp al, 0x02 ; get key no wait
-jne .s3
-call get_key_no_wait
-jmp .return_to_offender
-.s3: cmp al, 0x03 ; get scancode no wait
-jne .s4
-call get_scancode_no_wait
-jmp .return_to_offender
-.s4: cmp al, 0x04 ; get timer
-jne .s5
-mov eax, dword [TIMERVAL]
-jmp .return_to_offender
-.s5: cmp al, 0x05 ; short wait (hlt)
 jne .s86
-hlt
+call get_scancode
 jmp .return_to_offender
 .s86: cmp al, 0x86 ; v86 interrupt call
 je .v86int

handler.nasm

@@ -1,38 +1,71 @@
-global PROC_SWITCH
-PROC_SWITCH: dw 0
+oldscancodesToAscii: db 0, 0 ; 0x00 - 0x01
+db "1234567890" ; 0x02 - 0x0B
+db "-=" ; 0x0C - 0x0D
+db 0, 0 ; 0x0E - 0x0F
+db "qwertyuiop[]" ; 0x10 - 0x1B
+db 0, 0 ; 0x1C - 0x1D
+db "asdfghjkl;'`" ; 0x1E - 0x29
+db 0 ; 0x2A
+db "\zxcvbnm,./" ; 0x2B - 0x35
+db 0 ; 0x36
+db '*' ; 0x37
+db 0 ; 0x38
+db ' ' ; 0x39
+db 'C'
+scancodesToAsciiEnd:
+cursorCurrent: dd 0xb8000 + (80*6*2)
+global oldkeyboardHandler
+oldkeyboardHandler:
+push eax
+push ebx
+push ds
+mov ax, 0x10
+mov ds, ax
+xor eax, eax
+in al, 0x60
+cmp eax, 0x3A
+jg .done
+mov al, [oldscancodesToAscii+eax]
+test al, al
+jz .done
+mov ebx, [cursorCurrent]
+mov byte [ebx], al
+add dword [cursorCurrent], 2
+mov byte [KBDWAIT], 1
+.done:
+mov al, 0x20
+out 0x20, al
+pop ds
+pop ebx
+pop eax
+iret
+
+KBDWAIT: db 0
+oldkbd_wait:
+mov byte [KBDWAIT], 0
+.loop:
+hlt
+movzx eax, byte [KBDWAIT]
+test eax, eax
+jz .loop
+ret
 
 global TIMERVAL
-global TIMERVAL_FRAC
 TIMERVAL: dd 0
-TIMERVAL_FRAC: dd 0
 global timerHandler
 timerHandler:
 push eax
 push ds
 mov ax, 0x10
 mov ds, ax
-; Value from PITPgrm
-add dword [TIMERVAL_FRAC], 0xfffdb8d0
-adc dword [TIMERVAL], 0
+;inc byte [(0xb8000 + (80*8*2))]
+inc dword [TIMERVAL]
 mov al, 0x20
 out 0x20, al
-; Check task switch
-movzx eax, word [PROC_SWITCH]
-test eax, eax
-jnz task_switch
 pop ds
 pop eax
 iret
 
-extern save_current_task_int
-task_switch:
-mov word [PROC_SWITCH], 0
-pop ds
-pop eax
-call save_current_task_int
-iret
-
-
 global picInit
 picInit:
 mov al, 0x11  ; initialization sequence

kbd.c

@@ -1,11 +1,6 @@
 #include "interrupt.h"
 #include "kbd.h"
 
-extern uint16_t PROC_SWITCH;
-__attribute__((__noreturn__))
-__attribute__((__no_caller_saved_registers__))
-extern void ret_current_task_int();
-
 uint8_t scancodesToAscii[0x3B] =
 "\0\0" // 0x00 - 0x01
 "1234567890" // 0x02 - 0x0B
@@ -74,8 +69,6 @@ void keyboardHandler(struct interrupt_frame *frame) {
         "mov %%ax, %%ds\n"
         ::"a"(old_ds)
     );
-    if (key == KEY_F12) PROC_SWITCH = 1;
-    if (key == KEY_F11) ret_current_task_int();
 }
 
 __attribute((__no_caller_saved_registers__))
@@ -113,18 +106,3 @@ uint16_t get_scancode() {
     return k;
 }
 
-__attribute((__no_caller_saved_registers__))
-uint8_t get_key_no_wait() {
-    uint8_t k = _LSTKEY_ASCII;
-    _LSTKEY_ASCII = 0;
-    return k;
-}
-
-__attribute((__no_caller_saved_registers__))
-uint16_t get_scancode_no_wait() {
-    uint16_t k = _LSTKEY_SCAN | (_LSTKEY_ASCII << 8);
-    _LSTKEY_SCAN = 0;
-    _LSTKEY_ASCII = 0;
-    return k;
-}
-

kernel.c

@@ -190,11 +190,9 @@ Protected Only (1MB+)
 280000 - 300000 Disk Cache (512kB)
 300000 - 310000 Task Stack (64kB)
 310000 - 320000 Interrupt Stack (64kB)
-320000 - 400000 Free (896kB)
-400000 - 700000 Free (3mB)
-700000 - 800000 Kernel Stack (1mB)
- 800000 -  F00000 Usermode Code (7mB)
- F00000 - 1000000 Usermode Stack (1mB)
+320000 - 400000 Kernel Stack (896kB)
+400000 - 700000 Usermode Code (3mB)
+700000 - 800000 Usermode Stack (1mB)
 */
 
 void DrawScreen(uint16_t *vga) {
@@ -249,8 +247,13 @@ void RestoreVGA() {
 }
 
 int32_t fileCount, fileOffset;
+// We store dir entries in usermode space,
+// which is nice because there's nothing after,
+// but it does mean we need to reload the dir
+// after every task called. This might be fine,
+// since the task might have modified the directory.
 extern char _USERMODE;
-dirent *const DirEntries = (dirent*)0x400000;
+dirent *const DirEntries = (dirent*)&_USERMODE;
 #define MAXDISPFILES 16
 void PrintFileList(uint16_t *vga) {
     uint16_t *vga_text = &((uint16_t *)vga)[80*6+3];
@@ -374,20 +377,7 @@ void FileSelect() {
                 for (int i = 0; i < DirEntries[fileHovered].namelen; i++)
                     current_path[current_path_end + i] = DirEntries[fileHovered].name[i];
                 current_path[current_path_end + DirEntries[fileHovered].namelen] = 0;
-                {
-                    // Give userspace mem (8MB)
-                    uintptr_t process_page0 = add_pages(4|2|1);
-                    uintptr_t process_page1 = add_pages(4|2|1);
-                    asm("xchg %bx,%bx");
-                    // Page blocks are 4MB
-                    move_pages(process_page0 >> 22, (uintptr_t)&_USERMODE >> 22);
-                    move_pages(process_page1 >> 22, ((uintptr_t)&_USERMODE >> 22) + 1);
-                    asm("xchg %bx,%bx");
                 create_child(GetFreeStack(), (uintptr_t)HexEditor, 1, current_path);
-                    // Free userspace mem
-                    free_pages(process_page0 >> 22);
-                    free_pages(process_page1 >> 22);
-                }
                 current_path[current_path_end] = 0;
                 RestoreVGA();
                 reload = 1;
@@ -398,18 +388,7 @@ void FileSelect() {
                 for (int i = 0; i < DirEntries[fileHovered].namelen; i++)
                     current_path[current_path_end + i] = DirEntries[fileHovered].name[i];
                 current_path[current_path_end + DirEntries[fileHovered].namelen] = 0;
-                {
-                    // Give userspace mem (8MB)
-                    uintptr_t process_page0 = add_pages(4|2|1);
-                    uintptr_t process_page1 = add_pages(4|2|1);
-                    // Page blocks are 4MB
-                    move_pages(process_page0 >> 22, (uintptr_t)&_USERMODE >> 22);
-                    move_pages(process_page1 >> 22, ((uintptr_t)&_USERMODE >> 22) + 1);
                 create_child(GetFreeStack(), (uintptr_t)TextViewTest, 1, current_path);
-                    // Free userspace mem
-                    free_pages(process_page0 >> 22);
-                    free_pages(process_page1 >> 22);
-                }
                 current_path[current_path_end] = 0;
                 RestoreVGA();
                 reload = 1;
@@ -476,34 +455,6 @@ void FileSelect() {
     }
 }
 
-// TODO Move this somewhere else, maybe configurable & with timer handler
-void PITPgrm() {
-    const uint32_t base_clk = 3579545;
-    const uint16_t reload_v = 1194;
-    // (base_clk / 3) / reload_v = ~999.31463Hz
-
-    // 32.32 Fixed point
-    const uint64_t irq_ms = (uint64_t)reload_v * 3000LL * ((1LL << 42) / (uint64_t)base_clk / (1LL << 10));
-    // irq_ms = 4294818000 (0xfffdb8d0)
-    // We don't actually use this here, but in handler.nasm
-    // for now, eventually this should be in C
-
-    asm volatile(
-        "cli\n"
-        "movb $0b00110100, %%al\n"
-        "outb %%al, $0x43\n"
-        :::"%eax"
-    );
-    uint32_t clobber_eax;
-    asm volatile(
-        "outb %%al, $0x40\n"
-        "movb %%ah, %%al\n"
-        "outb %%al, $0x40\n"
-        "sti\n"
-        :"=a"(clobber_eax):"a"(reload_v)
-    );
-}
-
 int MakeSystemVolume(uint8_t sysPartition);
 void MakeMBRPartitions();
 void SystemRun(uint8_t sysPartition) {
@@ -512,7 +463,6 @@ void SystemRun(uint8_t sysPartition) {
     DrawScreen((uint16_t*)0xb8000);
 
     InitDisk();
-    PITPgrm();
 
     // Check for FAT partition
     {

paging.c

@@ -1,7 +1,7 @@
 #include "paging.h"
 
 uint32_t page_directory[1024] __attribute__((aligned(4096)));
-uint32_t page_tables[128][1024] __attribute__((aligned(4096)));
+uint32_t page_tables[4][1024] __attribute__((aligned(4096)));
 
 void enable_paging() {
     asm(
@@ -21,6 +21,7 @@ void map_pages(uintptr_t page, uintptr_t num_pages, uintptr_t phy_address, char
 
     // Each page is 4K, Each page table is 4M
     uintptr_t page_dir_entry = page >> 10;
+    if (page_dir_entry >= 4) return;
     uintptr_t page_index = page & 0x3ff;
     if (page_index + num_pages > 1024) return;
 
@@ -31,93 +32,11 @@ void map_pages(uintptr_t page, uintptr_t num_pages, uintptr_t phy_address, char
         page_tables[page_dir_entry][page_index + i] = phy_address + (i * 0x1000) | access_flags;
 }
 
-// Marks a 4MB page directory index unused, *without* freeing physical memory
-void mark_pages_unused(uint16_t page_dir_idx) {
-    if (page_dir_idx >= 1024) return;
-    // Supervisor, R/W, Not Present
-    page_directory[page_dir_idx] = 2;
-}
-
-// Bitmap of physical memory usage
-uint8_t PhyMapArr[1024/8];
-
-// Marks a 4MB page directory index unused, along with underlying physical memory
-void free_pages(uint16_t page_dir_idx) {
-    // Get first entry of page table
-    uint32_t *page_table = (uint32_t*)(page_directory[page_dir_idx] != 2 ? (uintptr_t)page_directory[page_dir_idx] & 0xfffff000 : 0);
-    if (!page_table) return;
-
-    // Free physical memory
-    uint32_t phy_address = page_table[0] & 0xfffff000;
-    uint32_t phy_address_4mb = phy_address >> 22;
-    uint32_t map_idx = phy_address_4mb >> 3;
-    uint32_t bit_idx = phy_address_4mb & 7;
-    // Clear bit
-    PhyMapArr[map_idx] &= ~(1 << bit_idx);
-
-    // Mark unused
-    mark_pages_unused(page_dir_idx);
-}
-
-// Gets an unused 4MB page directory index. Return -1 if no free pages.
-uint16_t get_unused_pages() {
-    for (int i = 0; i < 1024; i++)
-        if (page_directory[i] == 2) return i;
-    return -1;
-}
-
-// Gets physical address of 4MB unused area of physical memory. This will have to be mapped to virtual memory space to be used.
-uint32_t get_phy_mem() {
-    for (int i = 0; i < sizeof(PhyMapArr); i++) {
-        // Fully used
-        if (PhyMapArr[i] == 0xff) continue;
-        // At least one bit must be free
-        uint8_t bits = PhyMapArr[i];
-        for (int j = 0; j < 8; j++)
-            if (!(bits & (1 << j))) return (i << 25) + (j << 22);
-    }
-    return -1;
-}
-
 // User, R/W, Present
 #define USERACCESS (4|2|1)
 // Supervisor, R/W, Present
 #define SUPERACCESS (2|1)
 
-// Returns a pointer to a newly mapped 4MB memory chunk
-uintptr_t add_pages(char access_flags) {
-    // Get free physical space
-    uint32_t phy_mem = get_phy_mem();
-    if (phy_mem == -1) return -1;
-
-    // Get free virtual space
-    uint16_t free_ent = get_unused_pages();
-    if ((int16_t)free_ent == -1) return -1;
-    uintptr_t page = free_ent << 10;
-
-    // Mark page directory entry present, pointing to page table
-    page_directory[free_ent] = ((uintptr_t)&page_tables[free_ent]) | USERACCESS;
-    
-    // Map pages to physical address
-    map_pages(page, 1024, phy_mem, access_flags);
-
-    // Mark physical memory used
-    uint32_t phy_address_4mb = phy_mem >> 22;
-    uint32_t map_idx = phy_address_4mb >> 3;
-    uint32_t bit_idx = phy_address_4mb & 7;
-    // Set bit
-    PhyMapArr[map_idx] |= 1 << bit_idx;
-
-    // Return virtual address
-    return page << 12;
-}
-
-// Copies 4MB groups of pages
-void move_pages(uint16_t src_page_dir_idx, uint16_t dest_page_dir_idx) {
-    if (src_page_dir_idx >= 1024 || dest_page_dir_idx >= 1024) return;
-    page_directory[dest_page_dir_idx] = page_directory[src_page_dir_idx];
-}
-
 void init_paging() {
     for (int i = 0; i < 1024; i++)
         // Supervisor, R/W, Not Present
@@ -132,15 +51,13 @@ void init_paging() {
     // Next 4MB: Kernel
     map_pages(0x00400000 >> 12, 1024, 0x00400000, SUPERACCESS);
 
+    // Next 8MB: Usermode
+    map_pages(0x00800000 >> 12, 1024, 0x00800000, USERACCESS);
+    map_pages(0x00C00000 >> 12, 1024, 0x00C00000, USERACCESS);
+
     // We aren't using page directory permissions
     for (int i = 0; i < 4; i++)
         page_directory[i] = ((uintptr_t)&page_tables[i]) | USERACCESS;
 
-    // Mark all physical memory free TODO Check memory size
-    for (int i = 0; i < sizeof(PhyMapArr); i++)
-        PhyMapArr[i] = 0;
-    // Mark lowest 8MB as used
-    PhyMapArr[0] = 3;
-
     enable_paging();
 }

paging.h

@@ -1,6 +1,3 @@
 #include <stdint.h>
 
-void free_pages(uint16_t page_dir_idx);
-uintptr_t add_pages(char access_flags);
-void move_pages(uint16_t src_page_dir_idx, uint16_t dest_page_dir_idx);
 void init_paging();

progs.c

@@ -1,23 +1,21 @@
 #include "progs.h"
-#include "paging.h"
 #include "file.h"
 
 extern char _USERMODE, _USERMODE_END;
-static uintptr_t USERMODE_STACK = (uintptr_t)&_USERMODE_END - 0x100000;
 extern uint32_t create_user_child(uint32_t esp, uint32_t eip, uint32_t argc, ...);
-void programLoadTestInner(char *path) {
+void ProgramLoadTest(char *path) {
     uint16_t *vga_text = (uint16_t *)0xb8000;
     for (int i = 0; i < 80*25; i++)
         vga_text[i] = 0x0f00;
     uint32_t successcount;
-
     uint8_t *diskReadBuf = (uint8_t *)&_USERMODE;
     {
         uint32_t err;
         dirent de;
         err = path_getinfo(path, &de);
-        if (de.size > 0xE00000 || err) {
+        if (de.size > 0x300000 || err) {
             vga_text += printStr("File too large or error.", vga_text);
+            kbd_wait();
             return;
         }
         FILE file;
@@ -47,8 +45,7 @@ void programLoadTestInner(char *path) {
     vga_text = nextLine(vga_text,(uint16_t*)0xb8000);
     vga_text += printStr("Press any key to run.", vga_text);
     kbd_wait();
-    uint32_t res = create_user_child(USERMODE_STACK, (uintptr_t)&_USERMODE, 0);
-
+    uint32_t res = create_user_child((uintptr_t)&_USERMODE_END, (uintptr_t)&_USERMODE, 0);
     union V86Regs_t regs;
     regs.w.ax = 3; // text mode
     V8086Int(0x10, &regs); 
@@ -60,18 +57,5 @@ void programLoadTestInner(char *path) {
     vga_text += printStr(" (0x", vga_text);
     vga_text += printDword(res, vga_text);
     vga_text += printStr("). Press any key to exit.", vga_text);
-}
-void ProgramLoadTest(char *path) {
-    // Get free memory (8MB)
-    uintptr_t process_page0 = add_pages(4|2|1);
-    uintptr_t process_page1 = add_pages(4|2|1);
-    // Map usermode memory
-    move_pages(process_page0 >> 22, (uintptr_t)&_USERMODE >> 22);
-    move_pages(process_page1 >> 22, ((uintptr_t)&_USERMODE >> 22) + 1);
-    // Inner program
-    programLoadTestInner(path);
     kbd_wait();
-    // Free process memory
-    free_pages(process_page0 >> 22);
-    free_pages(process_page1 >> 22);
 }

task.nasm

@@ -5,8 +5,9 @@ ltr ax
 ret
 
 global task_ptr
-task_ptr: equ (0x310000)
+task_ptr: equ (0x310000-4)
 
+; TODO Is varargs too compiler dependent?
 ; extern void create_child(uint32_t esp, uint32_t eip, uint32_t argc, ...);
 global create_child
 create_child:
@@ -59,101 +60,6 @@ push 0x18 | 3
 push eax
 iret
 
-; save task
-; stack contains caller, eip, cs, eflags(, esp, ss)
-global save_current_task_new
-save_current_task_new:
-push ds
-push ebx
-push eax
-push 0x10
-pop ds
-; 0 eax, 4 ebx, 8 ds, 12 caller, 16 eip, 20 cs, 24 eflags(, 28 esp, 32 ss)
-; location to save task
-mov ebx, dword [0x318000]
-; code & stack
-mov eax, dword [esp+16]
-mov dword [ebx+0], eax  ; eip
-mov eax, dword [esp+20]
-mov dword [ebx+4], eax  ; cs
-cmp ax, 0x08
-; if we're not in code segment, save stack info
-je .curr_stack
-mov eax, dword [esp+24]
-mov dword [ebx+8], eax  ; eflags
-mov eax, dword [esp+28]
-mov dword [ebx+12], eax ; esp
-mov eax, dword [esp+32]
-mov dword [ebx+16], eax ; ss
-jmp .seg_regs
-; if we're in code segment, we save current info, minus interrupt stack
-.curr_stack:
-mov eax, dword [esp+24]
-mov dword [ebx+8], eax  ; eflags
-lea eax, [esp+28]
-mov dword [ebx+12], eax ; esp before interrupt
-mov eax, ss
-mov dword [ebx+16], eax
-; segment regs
-.seg_regs:
-mov eax, dword [esp+8]
-mov dword [ebx+20], eax ; ds
-mov eax, es
-mov dword [ebx+24], eax
-mov eax, fs
-mov dword [ebx+28], eax
-mov eax, gs
-mov dword [ebx+32], eax
-; general regs besides esp
-mov eax, dword [esp+0]
-mov dword [ebx+36], eax ; eax
-mov eax, dword [esp+4]
-mov dword [ebx+40], eax ; ebx
-mov dword [ebx+44], ecx
-mov dword [ebx+48], edx
-mov dword [ebx+52], esi
-mov dword [ebx+56], edi
-mov dword [ebx+60], ebp
-pop eax
-pop ebx
-pop ds
-xchg bx,bx
-ret
-
-; return to current task
-global ret_current_task
-ret_current_task:
-xchg bx,bx
-push 0x10
-pop ds
-; location to get task
-mov ebx, dword [0x318000]
-mov ebp, [ebx+60]
-mov edi, [ebx+56]
-mov esi, [ebx+52]
-mov edx, [ebx+48]
-mov ecx, [ebx+44]
-mov gs, [ebx+32]
-mov fs, [ebx+28]
-mov es, [ebx+24]
-mov ds, [ebx+20]
-mov eax, [ebx+4] ; cs
-cmp ax, 0x08
-je .restore_stack 
-mov eax, [ebx+36]
-mov esp, ebx
-mov ebx, [ebx+40]
-iret
-.restore_stack:
-mov esp, [ebx+12]
-mov ss, [ebx+16]
-mov eax, [ebx+36]
-push dword [ebx+8]
-push dword [ebx+4]
-push dword [ebx]
-mov ebx, [ebx+40]
-iret
-
 ; return address in EAX
 ; return stack in ECX
 ; we can modify EAX, ECX, EDX

tests.c

@@ -1,5 +1,4 @@
 #include "tests.h"
-#include "paging.h"
 
 extern char *user_test();
 extern uint32_t create_user_child(uint32_t esp, uint32_t eip, uint32_t argc, ...);
@@ -27,17 +26,8 @@ void ReloadUser() {
         *d++ = *s++;
 }
 char TestUser() {
-    // Get free memory (8MB)
-    uintptr_t process_page0 = add_pages(4|2|1);
-    uintptr_t process_page1 = add_pages(4|2|1);
-    // Map usermode memory
-    move_pages(process_page0 >> 22, (uintptr_t)&_USERMODE >> 22);
-    move_pages(process_page1 >> 22, ((uintptr_t)&_USERMODE >> 22) + 1);
     ReloadUser();
-    char *vga = (char *)(uintptr_t)create_user_child((uintptr_t)&_USERMODE_END - 0x100000, (uintptr_t)&_USERMODE, 0);
-    // Free process memory
-    free_pages(process_page0 >> 22);
-    free_pages(process_page1 >> 22);
+    char *vga = (char *)(uintptr_t)create_user_child((uintptr_t)&_USERMODE_END, (uintptr_t)&_USERMODE, 0);
     if ((uintptr_t)vga != 0xA0000) {
         return 1;
     }

tss.c

@@ -41,8 +41,8 @@ void write_tss() {
     tss_data->iomap_base = 0x80;
 
     // not technically TSS but set up task pointer
-    uint32_t *current_task_ptr = (uint32_t*)(0x310000);
-    *current_task_ptr = 0x310000-(1*4); // each task is 12 dwords, plus 1 for pointer
+    uint32_t *current_task_ptr = (uint32_t*)(0x310000-4);
+    *current_task_ptr = 0x310000-(20*4); // each task is 12 dwords, plus 1 for pointer
     /* TODO setup null recovery task at start */
 }
 extern void flushTSS();

usermode.nasm

@@ -27,8 +27,6 @@ mov dword [0xb8000+800], 0x0f000f00 | 'g' | ':' << 16
 mov dword [0xb8004+800], 0x0f000f00 | ' ' | '#' << 16
 mov dword [0xb8008+800], 0x0f000f00 | 'G' | 'P' << 16
 mov dword [0xb800C+800], 0x0f000f00 | 'F' | ' ' << 16
-.busy:
-jmp .busy
 mov eax, 0 ; command = 00h, get key
 int 0x21 ; OS call
 cmp al, 'd'