en:docs:kernel:doskrnl

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en:docs:kernel:doskrnl [2023/12/16 14:51] – prokusheven:docs:kernel:doskrnl [2024/05/25 02:43] (current) – prokushev
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 ====== DOSKRNL ====== ====== DOSKRNL ======
  
-DOSKRNL is a specialized FreeDOS kernel changed to support DOS in MVM. Mostly all FAT code removed as well as CONFIG.SYS parser. So it smaller in compare with original FreeDOS kernel. Also image format changed because different load logic.+DOSKRNL is a specialized FreeDOS kernel changed to support DOS in MVM. Mostly all FAT code removed as well as CONFIG.SYS parser. So it smaller in compare with original FreeDOS kernel. Also image format changed from exe to raw binary because slightly different load logic.
  
 ===== Initialization ===== ===== Initialization =====
  
-DOSKRNL loaded at address differ from standard DOS 0060:0000 address. osFree DOSKRNL expect unknown load address, but in low address of conventional memory.+DOSKRNL loaded at address differ from standard DOS 0060:0000 address. On test environment it was loaded to 0280:00, but [[https://archive.org/download/IBMOS2TechnicalDocumentation/KGUIDE20.PDF|OS/2 v 2.0 Kernel Design Guide]] says it is at 0070:0000. Later documentation says nothing about loading address. osFree DOSKRNL expects unknown load address, but in low address of conventional memory. Refer [[https://archive.org/download/IBMOS2TechnicalDocumentation/KGUIDE20.PDF|OS/2 v 2.0 Kernel Design Guide]] for memory map and initialization information.
  
 On DOSKRNL startup registers are following: On DOSKRNL startup registers are following:
  
   * CS:IP - starting point   * CS:IP - starting point
-  * SS:BP - pointer to the DOSKRNL init structure+  * SS:BP - pointer to the DOSKRNL init structure (also referenced as VDOS init in IBM documents)
   * SS:SP - stack pointer (size around 800 bytes)   * SS:SP - stack pointer (size around 800 bytes)
 +
 +Interrupts disabled.
  
 DOSKRNL init structure: DOSKRNL init structure:
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 | 26     | 1    | Current drive (1-A, 2-B, 3-C, ...)| | 26     | 1    | Current drive (1-A, 2-B, 3-C, ...)|
 | 27     | 1    | Boot drive (1-A, 2-B, 3-C, ...) | | 27     | 1    | Boot drive (1-A, 2-B, 3-C, ...) |
-| ????   | ???  | ???? |+| 28     | 1    | Last drive (1-A, 2-B, 3-C, ...) | 
 +| ???    | ???  | ??? |
  
 DEVICES is ASCIIZ string with list of DOS devices to be loaded divided by 0AH DEVICES is ASCIIZ string with list of DOS devices to be loaded divided by 0AH
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 SHELL is ASCIIZ string. SHELL is ASCIIZ string.
  
-SHELL arguments is ASCIIZ string (first byte is as string length, string ends with 0dh)+SHELL arguments is ASCIIZ string (first byte is a string length, string ends with 0dh)
  
 VDD is linked list of structures: VDD is linked list of structures:
  
-VDDs linked list (in init area) in standard DOS Device drivers format+VDDs linked list in standard DOS Device drivers format. Entry can be placed in HMA, so need to be sure A20 enabled for such entries. Named as DOSDDTYPE in DDK
  
 ^ offset ^ Size ^ Description ^ ^ offset ^ Size ^ Description ^
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 | Free              | [BP+0]:0 | | Free              | [BP+0]:0 |
 | DOSKRNL           | ???:0 | | DOSKRNL           | ???:0 |
-| some data         | ??? |+| Some data (VDD entries was found here) | ??? |
 | CMOS Data         | 40:0 | | CMOS Data         | 40:0 |
 | Interrupt vectors | 0:0  | | Interrupt vectors | 0:0  |
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   * DOS   * DOS
   * BREAK   * BREAK
 +  * FCBS
 +  * LASTDRIVE
  
 todo add more info here todo add more info here