Atari 400 Technical Reference Manual page 237

sequence and is set to 0 at the completion; if a system reset
occurs while the value is nonzero, the power-up sequence will be
reinitiated (rather than initiating a system reset sequence).
N12 DOSVEC [000A,21 -- Noncartridge control vector
At the beginning of power-up the
as
sets DOSVEC to point to the
"blackboard" routine; DOSVEC can then be altered as a consequence
of a diskette-boot or cassette-boot <as explained in Section 10) to
establish a new control program. Control will be passed through
DOSVEC on all power-up and system reset conditions in which a
cartridge does not take control first.
System Reset
N13 WARMST [0008,11 -- Warmstart flag
WARMST equals $FF during a system reset (warmstart)
initialization and equals 0 during a power-up initialization
(coldstart).
P. INTERRUPTS
See Section 6 for a discussion of interrupt processing.
Pl CRITIC [0042,11 -- Critical code section flag
CRITIC is used to signal to the VB LANK interrupt processor that a
critical code section is executing without IRG interrupts being
inhibited; the VB LANK interrupt processor will'stop interrupt
processing after stage 1 and before stage 2, Just as if the 6502
processor I bit were set, when CRITIC is set.
CRITIC equal to zero indicates that the currently executing code
section is noncritical, while any nonzero value indicates that the
currently executing code section is critical.
P2 POKMSK [0010,11 -- POKEY interrupt mask
POKMSK is a software maintained interrupt mask that is used in
conJunction with the enabling and disabling of the various POKEY
interrupts. This mask is required because the POKEY interrupt
enable
registe~
IRGEN
[D20EJ
is a write-only register, an4
~t
any
point in time the system can have several users independently
enabling and disabling POKEY interrupts. POKMSK is updatedbv the
OPERATING SVSTEMC016555 -- Appendix' L
252