Global System Tables

Contents:

System information block
IO port owners table
Interrupt receivers table
Message receivers table
Message queue blocks
User Connection Table

This information contains current information about the system. It's main purpose is for quick access from applications and drivers.
 

Address	Size (bytes)	Use
		Memory
0x00A00	4	Number of pages of RAM installed
0x00A04	4	Number of pages free
0x00A08	4	Address of system page directory
0x00A0C	4	Address of PAM
0x00A10	16	-
		System
0x00A20	4	Address of IO port owner table
0x00A24	4	Number of pages in IO port owner table
0x00A28	4	Address of interrupt receiver table
0x00A30	4	Used for temporary storage
0x00A34	16	-
		Time
0x00A40	4	Timer tick low (fractions of a millisecond)
0x00A44	4	Timer tick high (milliseconds since boot)
0x00A48	4	Timer rollover counter (every 49.71 days)
0x00A4C	2	Current task
0x00A4E	1	Current thread
0x00A4F	1	Scheduler status flags
0x00A50	4	Value of timer tick high last task switch (0 for none)
0x00A54	4	Task info table address
0x00A58	4	Current number of tasks
0x00A5C	2	Lowest valid task ID
0x00A5E	2	-
		Network
0x00A60	32	-
		Message
0x00A80	4	Address of receiver table
0x00A84	2	Receiver table size (in pages)
0x00A86	2	Highest Receiver ID
0x00A88	4	Number of valid message receivers
0x00A8C	20	-
		File
0x00AA0	32	-
		User
0x00AC0	4	Address of  user connection table
0x00AC4	4	Current active user connection entry number
0x00AC8	4	Address of active user connection
0x00ACC	4	Current number of user connections
0x00AD0	16	-
		Miscellaneous
0x00BF8	4	Last secure local keypress
0x00BFC	4	Last secure local keypress number

 

This table contains 65536 entries, 1 word for each port containing the owners code segment number. The lower 2 bits of this word are undefined and may be used for anything.
 

This page keeps track of which code to call for each cpu generated interrupt. Each of the 32 interrupts has a table made up of 16 entries (8 bytes each). Each interrupt takes up 256 bytes, so offset 0x200 within the page would be the start of the first entry in the table for the third interrupt.

Each entry in each table has this format:
 

Offset	Size	Use
0	4	Offset for far call
4	2	Code ID of owner (it's CS)
6	1	Reserved
7	1	Flags    Bit   Meaning when set     0     Entry in use     1-7   Reserved

 

Each message queue has an associated receiver ID. For each receiver ID this table has a 8 byte entry with this format:
 
 

Offset	Size	Use
00	4	address of queue or offset
04	2	code ID
06	1	reserved
07	1	Port flags    Bit  Meaning when '1'     0    Entry in use     1    Entry has queue

 

Each message queue block starts with this header:
 

Offset	Size	Use
00	4	Number of allocated pages for queue
04	4	Offset for last entry
08	4	Offset for head entry
0C	4	Offset for tail entry
10		Start of entries

 

Each entry has this format:
 

Offset	Size	Use
000	4	Sender ID
004	4	Data1
008	4	Data2
00C	4	Function

 

This is actually a page containing 2 tables. The page is broken up like this:
 
 

Offset	Size	Use
0000	128	Device connection entries
0080	3968	User connection entries

 

Each device type has a device connection entry in this format:
 

Offset	Size	Use
000	4	Message port ID (0 for none)
004	4	Connection ID currently connected to

 

Each user connection to the local user interface has an ID. For each ID there is an entry in this table corresponding to the message port ID for the owner of that connection. The format of each entry is:
 

Offset	Size	Use
000	4	Owners message port
004	2	Connection flags    Bit  Meaning when '1'     0    Connected to keyboard     1    Connected to video     2    Connected to mouse     3    Connected to sound     4    Connected to joystick
006	1	-
007	1	General Flags    Bit  Meaning when '1'     0    Entry in use/valid