Atari 400 Technical Reference Manual page 23

2 OPERATING SYSTEM FUNCTIONAL ORGANIZATION
This section describes the various subsystems of the resident OS in
general terms.
InputlOutput Subsystem
The InputlOutput
(1/0)
subsystem provides a high-level interface
between the programs and the hardware. Most functions are
device-independent, such as the reading and writing of character data;
yet provisions have been made for device-dependent functions as well.
All peripheral devices capable of dealing with character data have
individual symbolic names (such as K,D,P, etc). and can be accessed
using a Central
1/0
(CIO) routine.
A RAM data base provides access to controllers
(Jo~sticks
and paddle
controllers), which do not deal with character data. This RAM data
base is periodically updated to show the states of these devices.
INTERRUPT PROCESSING
The interrupt system handles all hardware interrupts in a common
and consistent manner. By default, all interrupts are fielded by
the OS. At you r dis c ret ion, in d i v i d u a lin t err u p t s
(0
r
groups of interrupts) can be fielded by the application program.
INITIALIZATION
The system provides two levels of initialization: power up and
system reset. The OS performs power-up initialization each time
the system power is switched to ON, and system reset
initialization is performed each time the [SYSTEM. RESET]
ke~
is
pressed.
Power-Up
The OS examines and notes the configuration of the unit whenever
the system power is switched to ON. The system performs the following
tasks at power up:
OPERATING SYSTEM C016555 -- Section 2
22