use32                           ; we want 32bit addressing
        ORG   0x400000          ; where our program is loaded to
        jmp   start             ; jump to the start of program.
        db    'DEX1'            ; DexOS checks for this
start:
        mov   ax,18h            ; load ax with the nonlinear data desetor
        mov   ds,ax             ; move it into DS and ES
        mov   es,ax             ; as you can not move it directly.

        mov   edi,Functions     ; this is the interrupt
        mov   al,0              ; we use to load the Dex.inc
        mov   ah,0x0a           ; with the address to DexOS functions.
        int   40h               ; int 40h = to Dos int 21h.
    

since the above tut was written, the ORG is now " 0x400000" not "0x200000"

this is a old list, many more function have bean added

       ;start of program add this        mov   eax,[return]        mov   [eax],esp        mov   esp,0x800000        ; just before exit do this        mov   eax,[return]        mov   esp,[eax]    

"this is a old list, many more function have bean added"
The stuff should get updated ... the manuals and examples

Thanks.

> Great ?

Maybe :shock:

> To make addressing identical in real mode and protected mode, we set the base of the code and data descriptors to DS * 16. This number is computed at run-time.

Inside the kernel and in one low memory 64-KiB segment only ? CS also ? Why doesn't the kernel set them all before starting the app ? Seems NOT to be ZERO based then ... the base is somewhere >0 in low memory ?

> We also have a linear descriptors (8h) for writing directly to screen etc.

Any of them is ZERO based (VGA ram at $A0000, BIOS variables accessible, ...) ?

Any list of them all around ?

> based on a flat memory model, the basic idea is your are load to 4MB and you are free to use memory from 4MB to top of memory, you can get top of memory by calling
> can load drivers/modules to top of real memory and then you will have size of real ram, - size of loaded modules, will become top of memory.

* Kernel: in low memory
* Kernel's buffers: 1+1/16 Mi ... 4 Mi + x
* My application: 4 Mi + x ... "top"
* "top" ... physical top: drivers

Right ^^^ ? And 2 Mi changed to 4 Mi because the kernel became more
memory hoggy (look at Vi$ta for a really memory hoggy thing ) ?
And DexOS requires 8 MiB RAM at least ?

> you can call int 40h, with a function number, we tryed to keep them as close to Dos int 21h eg: to print string with int you would mov ah,09h

So I can bypass using the table, and AH is the function number, and AL a parameter / reserved for sub-functions ?

> but you could do something like this if you want a bigger stack

Brew a bigger stack anywhere above my app ? So in DexOS I can use memory without allocating, just respecting the "top" ?

The kernel DOES set them, its just to make sure

you want to point to vesa ram, VGA ram at $A0000, BIOS variables

So DexOS was never designed to be a desktop OS, but to be simple to code for and give the coder full control.

They are set to CS = 10h (which is same base as DS)

;
; DexOS Hello world // Compile with FASM
;

  format binary ; .DEX
  use32
  org  $400000         ; where our program is loaded to
  jmp  @f              ; jump to the start of program.
  db   'DEX1'
@@:
        mov  esi,tx1     ; this point's to our string.
        mov  ah,9
        int  $40         ; PrintString
        mov  ah,4
        int  $40         ; WaitForKeyPress
        ret

tx1:   db 'Hello world! ',13,0
    

DS, SS, ES, FS = 18h (which is set to realmode ds *16)
GS, = 8h (which is 0 based)
EAX=EBX=ECX=EDX=ESI=EDI=0, on app start, the ESP depends on load address, as "Dos" loads DexOS at differant address than "Bootprog"

;
; DexOS Hello world & register report // Compile with FASM
;

q=$500000

  format binary ; .DEX
  use32
  org  $400000         ; where our program is loaded to
  jmp  @f              ; jump to the start of program.
  db   'DEX1'
@@:
        pushfd         ; EFLAGS
        push eax       ; EAX
        call @f        ; EIP
@@:     mov eax,esp
        sub eax,8
        push eax       ; ESP
        push ebx       ; EBX
        push ecx       ; ECX
        push edx       ; EDX
        push esi       ; ESI
        push edi       ; EDI
        push ebp       ; EBP
        xor eax,eax
        mov ax,ss
        push eax       ; SS
        mov ax,cs
        push eax       ; CS
        mov ax,ds
        push eax       ; DS
        mov ax,es
        push eax       ; ES
        mov ax,fs
        push eax       ; FS
        mov ax,gs
        push eax       ; GS

        mov ax,$0A00
        mov edi,q
        int $40           ; Load table

        mov   esi,tx1           ; this point's to our string.
        call dword [q+36]       ; PrintString

        xor ecx,ecx
@@:     mov al,[tx2+ecx*4]
        call dword [q+44]       ; PrintCharCursor
        mov al,[tx2+1+ecx*4]
        call dword [q+44]       ; PrintCharCursor
        mov al,[tx2+2+ecx*4]
        call dword [q+44]       ; PrintCharCursor
        mov al,[tx2+3+ecx*4]
        call dword [q+44]       ; PrintCharCursor
        mov al,32
        call dword [q+44]       ; PrintCharCursor
        pop eax
        call dword [q+52]       ; WriteHex32
        mov  esi,tx3            ; EOL
        call dword [q+36]       ; PrintString

        inc cl
        cmp cl,16
        jnz @b

        mov   esi,tx4           ; this point's to our string.
        call dword [q+36]       ; PrintString

        call dword [q+16]       ; WaitForKeyPress

        mov   esi,tx5           ; this point's to our string.
        call dword [q+36]       ; PrintString

;       ud2
        ret

tx1:   db 'Hello world! Look at it:',13,0
tx2:   db 'GS  FS  ES  DS  CS  SS  EBP EDI ESI EDX ECX EBX ESP EIP EAX EFLG'
tx3:   db 13,0
tx4:   db 'Press any key',13,0
tx5:   db 'Exiting',13,0
    

DexOS was never designed to be a desktop OS

mov al,0mov ah,2int 40h    

- DexOS has startup problems (not even verify that CPU is in RM ?)

2. Waitkey using int is :

Code:

mov al,0
mov ah,2
int 40h
    

4. DexOS Reads/writes to a fat16 hdd and reads fat32 hdd, i do not know why you say it can not reads/writes to fat16, as it can, but only the first partion.

As for not reading Hdd maybe your Hdd is fat16 ?, as fat32 only in that

        use32
        ORG    0x400000                             
        jmp    start                                
        db     'DEX1'                                
start:
        mov     esi,hello
        mov     ah,9
        int     40h

        mov     ah,02h
        int     40h

hello db 'Hello from protected mode!',0Dh,0Ah,0