Atari 400 Technical Reference Manual page 151

Save the I of records to boot. Save the load address. Save
the initialization address in CASINI [0002]
3. Move the record Just read to the load address specified.
4. Read the remaining records directly to the load
area.
5. JSR to the load address+6 where a multistage boot process
can continue; the carry bit will indicate the success of
this operation (carry set=error, carry reset=success).
6. JSR indirectly through CASINI for initialization of the
application; the application will initialize and return.
7. JMP indirectly through DOSVEC to transfer control to the
application.
Pressing the [SYSTEM. RESET] key after the application is fully booted
will cause steps 6 and 7 to be repeated.
NOTE: After the initial boot process is complete, the booter will
transfer control to the seventh byte of the first record; at this
point the software should continue the boot process (if it is a
multistage boot) and then stop the cassette drive, which due to a
system bug will still be running, using the following instruction
se~uence:
LOA #.3C
STA PACTL (0302]
The application should then set a value in MEMLO [0237] that
points to the first free RAM location beyond the software Just
booted, as shown below:
LOA IENO+l
STA MEHLO
STA APPMHI
LOA IENO+1/256
STA MEMLO+l
STA APPMHI+l
If the booted software is to take control of the system at the end
of the boot operation, the vector DOSVEC (OOOA] must be set up
by
the application at this time; OOSVEC points to the restart entry
for the booted application. If the booted software is not to take
control, then OOSVEC should remain unchanged.
LOA
STA
LDA
STA
IRESTRT
OOSVEC
#RESTRT/256
OOSVEC+l
; RESTART LSB
NOTE: The initialization point is entered on every system reset
and power-up; internal initialization can take place
here.
OPERATING SYSTEM C016555 -- Section 10
166