lots of in progress stuff

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 "i686-elf" -m32 -mgeneral-regs-only -ffreestanding\
+CFLAGS = -target "i386-elf" -m32 -mgeneral-regs-only -ffreestanding\
-		 -march=i686 -fno-stack-protector -Wno-int-conversion -nostdlib -c
+		 -march=i386 -fno-stack-protector -Wno-int-conversion -nostdlib -c
 LFLAGS = -Wl,--gc-sections -Wl,--print-gc-sections -m32 -nostartfiles -nostdlib
 
 ifeq ($(OUTFILE),)

fault.nasm

@@ -70,10 +70,13 @@ 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
@@ -91,9 +94,25 @@ jne .s1
 call get_key
 jmp .return_to_offender
 .s1: cmp al, 0x01 ; get scancode
-jne .s86
+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
+jmp .return_to_offender
 .s86: cmp al, 0x86 ; v86 interrupt call
 je .v86int
 cmp ax, 0x86D8 ; get v86 data pointer

handler.nasm

@@ -1,71 +1,38 @@
-oldscancodesToAscii: db 0, 0 ; 0x00 - 0x01
+global PROC_SWITCH
-db "1234567890" ; 0x02 - 0x0B
+PROC_SWITCH: dw 0
-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
-;inc byte [(0xb8000 + (80*8*2))]
+; Value from PITPgrm
-inc dword [TIMERVAL]
+add dword [TIMERVAL_FRAC], 0xfffdb8d0
+adc dword [TIMERVAL], 0
 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

@@ -1,6 +1,11 @@
 #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
@@ -69,6 +74,8 @@ 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__))
@@ -106,3 +113,18 @@ 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

@@ -190,9 +190,11 @@ Protected Only (1MB+)
 280000 - 300000 Disk Cache (512kB)
 300000 - 310000 Task Stack (64kB)
 310000 - 320000 Interrupt Stack (64kB)
-320000 - 400000 Kernel Stack (896kB)
+320000 - 400000 Free (896kB)
-400000 - 700000 Usermode Code (3mB)
+400000 - 700000 Free (3mB)
-700000 - 800000 Usermode Stack (1mB)
+700000 - 800000 Kernel Stack (1mB)
+ 800000 -  F00000 Usermode Code (7mB)
+ F00000 - 1000000 Usermode Stack (1mB)
 */
 
 void DrawScreen(uint16_t *vga) {
@@ -247,13 +249,8 @@ 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*)&_USERMODE;
+dirent *const DirEntries = (dirent*)0x400000;
 #define MAXDISPFILES 16
 void PrintFileList(uint16_t *vga) {
     uint16_t *vga_text = &((uint16_t *)vga)[80*6+3];
@@ -377,7 +374,20 @@ 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;
@@ -388,7 +398,18 @@ 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;
@@ -455,6 +476,34 @@ 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) {
@@ -463,6 +512,7 @@ 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[4][1024] __attribute__((aligned(4096)));
+uint32_t page_tables[128][1024] __attribute__((aligned(4096)));
 
 void enable_paging() {
     asm(
@@ -21,7 +21,6 @@ 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;
 
@@ -32,11 +31,93 @@ 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
@@ -51,13 +132,15 @@ 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

@@ -1,3 +1,6 @@
 #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

@@ -1,21 +1,23 @@
 #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 ProgramLoadTest(char *path) {
+void programLoadTestInner(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 > 0x300000 || err) {
+        if (de.size > 0xE00000 || err) {
             vga_text += printStr("File too large or error.", vga_text);
-            kbd_wait();
             return;
         }
         FILE file;
@@ -45,7 +47,8 @@ void ProgramLoadTest(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((uintptr_t)&_USERMODE_END, (uintptr_t)&_USERMODE, 0);
+    uint32_t res = create_user_child(USERMODE_STACK, (uintptr_t)&_USERMODE, 0);
+
     union V86Regs_t regs;
     regs.w.ax = 3; // text mode
     V8086Int(0x10, &regs); 
@@ -57,5 +60,18 @@ void ProgramLoadTest(char *path) {
     vga_text += printStr(" (0x", vga_text);
     vga_text += printDword(res, vga_text);
     vga_text += printStr("). Press any key to exit.", vga_text);
-    kbd_wait();
+}
+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

@@ -5,9 +5,8 @@ ltr ax
 ret
 
 global task_ptr
-task_ptr: equ (0x310000-4)
+task_ptr: equ (0x310000)
 
-; TODO Is varargs too compiler dependent?
 ; extern void create_child(uint32_t esp, uint32_t eip, uint32_t argc, ...);
 global create_child
 create_child:
@@ -60,6 +59,101 @@ 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

@@ -1,4 +1,5 @@
 #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, ...);
@@ -26,8 +27,17 @@ 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, (uintptr_t)&_USERMODE, 0);
+    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);
     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*)(0x310000-4);
+    uint32_t *current_task_ptr = (uint32_t*)(0x310000);
-    *current_task_ptr = 0x310000-(20*4); // each task is 12 dwords, plus 1 for pointer
+    *current_task_ptr = 0x310000-(1*4); // each task is 12 dwords, plus 1 for pointer
     /* TODO setup null recovery task at start */
 }
 extern void flushTSS();

usermode.nasm

@@ -27,6 +27,8 @@ 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'