DOSKRNL

DOSKRNL is a specialized DOS kernel changed to support DOS in MVM.

Startup

On DOSKRNL start SS:BP contains some structure which contains initial information for DOS kernel. Exact structure format not know. SS:SP contains stack pointer (initially point to area after init structure, size around 400 bytes)

Offset	Size	Description
0	2	First free segment after DOSKRNL
2	2	Size of memory - first free segment (paragraphs)
4	2	Size of init area (paragraphs)
6	2	Value of BREAK setting
8	2	Value of DOS setting
10	4	Far pointer to list of DOS DEVICE setting
14	4	Far pointer to SHELL (filepath only)
18	4	Far pointer to SHELL (arguments)
22	4	Pointer to linked list of VDD
26	1	Current drive (0-A, 1-B,…)
27	1	Boot drive (0-A, 1-B,…)
????	???	????

Memory map on DOSKRNL start:

Init area	[BP+0+BP+2-BP+4]:0
Free	[BP+0]:0
DOSKRNL	60:0
CMOS Data	40:0
Interrupt vectors	0:0

As in most DOS kernels, DOSKRNL moves initialization code to higher memory. But uses init structure, not BIOS INT 12h, for memory information.

VDDs linked list (in init area) in standard DOS Device drivers format

offset	Size	Description
0	4	Pointer to next device (Must be set to -1 for last device)
4	2	Attributes
Bit 15 = 1 if char device 0 if blk
if bit 15 is 1
Bit 0 = 1 if Current sti device
Bit 1 = 1 if Current sto output
Bit 2 = 1 if Current NUL device
Bit 3 = 1 if Current CLOCK dev
Bit 4 = 1 if SPECIAL
Bit 14 is the IOCTL bit
Bit 13 is the NON IBM FORMAT bit
6	2	Pointer to Device strategy entry point
8	2	Pointer to Device interrupt entry point
10	8	character device name field. Character devices set a device name. For block devices the first byte is the number of units

DOSKRNL search and initialize XMS driver and moves some parts to HMA. Most other initialization things is same. DOSKRNL initializes standard device drivers and adds and initializes VDDs, passed via init structure. Some things (at least COMMAND.COM, device drivers) also passed via init structure. not CONFIG.SYS. At the present time interface not investigated well.

CONFIG.SYS

CONFIG.SYS device information and some other settings not parsed by DOSKRNL, but passed via init structure. Here list of DOSKRNL options:

RMSIZE

DEVICE

SHELL

DOS

BREAK

todo add more info here

Also most of these setting can be adjusted via DOS Properties (aka DOS Settings). Refer OS/2 Version 2.0 Volume 2: DOS and Windows Environment for more information.

API

According different sources IBM DOSKRNL implements API on level of MS-DOS 5.x. osFree DOSKRNL supports API as in FreeDOS kernel. More information about implemented functions available here. DOSKRNL also implements some extensions to API mostly aimed to communicate with host system.

Supervisor calls

DOSKRNL uses SVC interface to call host functions.