3.5 The system vectors

As the system variables and vectors represent the lowest level of the operating system, application programs should access these only when absolutely necessary. Explicitly:

Do not alter any system variables that may not be altered.
Do not use any system variables if a function of the operating system could be called instead (Example: Mfpint).

The following list contains all system vectors of TOS:

vector

Description

LONG $000

Reset: SSP
This and the following memory cells contain a mirror image of the first eight bytes of the ROM. At a reset the value stored here is loaded into the supervisor stack pointer (though this is not meaningful; the 'real' stack is only installed later by the BIOS.

LONG $004

Reset: PC
At a reset the value found here is loaded into the program counter (PC). So one finds here the address that is jumped to on a reset.

LONG $008

Bus Error vector
Exception vector 2: Two bomblets
Bus errors arise when one attempts to access regions of memory to which access is not permitted. In supervisor mode this really can be only nonexistent memory areas. In user mode this can also happen in attempting to access hardware registers or regions below $800.

Normally this vector points to the TOS routine for the display of bombs (in this case just two).

LONG $00c

Address Error vector
Exception vector 3: Three bomblets
The 68000 and 68010 can access odd addresses only byte by byte. This exception is triggered if one nevertheless attempts a word or longword access (program counters or stack pointers too may contain no odd addresses).

LONG $010

Illegal Instruction Error vector
Exception vector 4: Four bomblets
An attempt was made to perform an illegal instruction. This vector is altered by many debuggers for using for break-points.

LONG $014

Division by Zero Error vector
Exception vector 5: No bomblets
Division was by 0 during a DIV command. Normally this vector points to an RTE instruction; that's why there are no bomblets.

LONG $018

CHK Instruction Exception vector
Exception vector 6: An exception was created by a CHK instruction.

LONG $01c

TRAPV Instruction Exception vector
Exception vector 7: An exception was created by a TRAPV instruction.

LONG $020

Privilege Violation Exception vector
Exception vector 8:
An attempt was made to execute an instruction that is permitted only in supervisor mode. On an Atari TT, the BIOS tests whether the corresponding instruction was a 'move sr,...': unlike on 68000s, this instruction is permitted only in supervisor mode on the TT. If this is the case, the BIOS will substitute the instruction 'move ccr,...' and attempt to keep the program running.

LONG $024

Trace Exception vector
Exception vector 9: If the trace bit is set in the status register, the address specified here is jumped to after every instruction.

LONG $028

Line-A-Vector
Exception vector 10: An attempt was made to execute an instruction that contained the value '$A' in the top four bits. At present this vector is used for the co-called Line-A routines.

LONG $02c

Line-F Exception vector
Exception vector 11: An attempt was made to execute an instruction that contained the value '$F' in the top four bits. It is used up to TOS 1.04 by GEM, and is intended actually for the programmming of a floating point unit (FPU).

LONG $030

Reserved

Exception vectors 12-23

LONG $05C

Reserved

LONG $060

Spurious Interrupt vector
Exception vector 24: Occurs if an interrupt has been triggered but the cause of it could not be ascertained.

LONG $064

Auto-vector Interrupt, Level 1
Unused

LONG $068

Auto-vector Interrupt, Level 2
Points to the handler for horizontal blanking.

LONG $06c

Auto-vector Interrupt, Level 3
Unused

LONG $070

Auto-Vector Interrupt, Level 4
Points to the handler for vertical blanking.

LONG $074

Auto-Vector Interrupt, Level 5
Unused

LONG $078

Auto-Vector Interrupt, Level 6
Points to the handler for MFP interrupts.

LONG $07c

Auto-Vector Interrupt, Level 7
Unused

LONG $080

TRAP#0
Exception vector 32
Vector for the 'TRAP #0' instruction. As it is not used by the operating system, it throws bomblets.

LONG $084

TRAP#1
Exception vector 33
Vector for the 'TRAP #1' instruction. Points to the Dispatcher for the GEMDOS functions.

LONG $088

TRAP#2
Exception vector 34
Vector for the 'TRAP #2 instruction'.
Depending on the value in d0, different system functions are started:

dec	hex	name
-2		vq_gdos
-1		address of VDI dispatcher
115	0x73	VDI
200	0xc8	AES
201	0xc9	_appl_yield
18219	0x472b	G+PLUS, is the value not 0x472b, then is it install

LONG $08c - LONG $0b0

TRAP#3 - TRAP#12
Exception vectors 35-44. Throws a corresponding number of bomblets, as they are not used currently by the operating system. However, there are external extensions that use these traps:

LONG $08c	TRAP#3 Exception vector 35 Is used only by Omega-Color-CAD, otherise without function.
LONG $090	TRAP#4 Exception-Vector 36 The MS-DOS Emulator SuperCharger use the Trap #4 for his Toolbox.
LONG $094	TRAP#5 Exception vector 37 Is used by Wind-XES. It is a modular accessory/control panel that lets you load in .WNX ("winks") applications which run concurrently under its environment. MidiShare a multi-tasking and real-time system for Midi program use this trap (also Trap #6).
LONG $098	TRAP#6 Exception vector 38 MidiShare a multi-tasking and real-time system for Midi program use this trap (also Trap #5).
LONG $0a0	TRAP#8 Exception vector 40 Cubase MROS from Steinberg use this trap.
LONG $0a4	TRAP#9 Exception vector 41 Cubase MROS from Steinberg use this trap.
LONG $0a8	TRAP#10 Exception vector 42 Is used by TapeBIOS. Serves for controlling a BandDrive at the ASCI-bus of the Atari. Cubase MROS from Steinberg use this trap also.

LONG $0b4

TRAP#13
Exception vector 45: Vector for the 'TRAP #13' instruction. Points to the Dispatcher for the BIOS functions.

LONG $0b8

TRAP#14
Exception vector 46: Vector for the 'TRAP #14' instruction. Points to the Dispatcher for the XBIOS functions.

LONG $0bc

TRAP#15
Not used by the operating system. NVDI and its print monitor make use of this vector.

LONG $0c0

reserves

Exception vectors 48-63.

LONG $0fc

Reserved

LONG $100

BUSY Interrupt vector
ST-MFP interrupt #0. Is triggered by the parallel port. Normally not used.

LONG $104

DCD-Interrupt
ST-MFP interrupt #1. Is triggered by the serial port (Carrier detect). Normally unused.

LONG $108

CTS-Interrupt
ST-MFP interrupt #2. Is triggered by the serial port (Clear to send). Normally unused.

LONG $10c

GPU Done vector
ST-MFP interrupt #3. Can be used by the blitter (when present) to indicate termination of an operation. Normally unused.

LONG $110

Baud-rate Generator
ST-MFP interrupt #4. Normally unused.

LONG $114

200Hz System Clock
ST-MFP interrupt #5. Points to the system clock interrupt and may not be altered under any circumstances (required for timing loops in TOS.

LONG $118

IKBD/MIDI
ST-MFP interrupt #6. Points to the handler for IKBD and MIDI interrupts.

LONG $11c

FDC/ACSI
ST-MFP interrupt #7. Normally unallocated.

LONG $120

Display Enable Signal
ST-MFP interrupt #8. Normally blocked.

LONG $124

RS-232 Transmit Error interrupt
ST-MFP interrupt #9. Is triggered by transmission errors when sending data via the serial port.

LONG $128

RS-232 Transmit Buffer Error interrupt
ST-MFP interrupt #10. Is triggered when the transmission of a single byte is completed and the transmit buffer is empty.

LONG $12c

RS-232 Receive Error interrupt
ST-MFP interrupt #11. Occurs at receive errors.

LONG $130

RS-232 Receive Buffer Full interrupt
ST-MFP interrupt #12. A complete character has been received by the serial port.

LONG $134

Unused
ST-MFP-Interrupt 13. Unused

LONG $138

RS-232 Ring Indicator interrupt
ST-MFP interrupt #14. Is triggered when the serial port detects an incomming call (e.g. when using a modem). As this interrupt is so easy to trigger, debuggers like to use it as a break signal.

LONG $13c

Monochrome Monitor Detect interrupt
ST-MFP-Interrupt 15. unused

LONG $140

TT-MFP interrupts

16 interrupt vectors for the second MFP in the Atari-TT.

LONG $17c

TT-MFP interrupts

LONG $180

TT-SCC interrupts

Space for the interrupt vectors of the SCC module in the Atari-TT.

LONG $1bc

TT-SCC interrupts

BIOS

The system variables

BIOS error-messages