NEC CP/M-86 - The Graphics Device Operating System (Gdos)

GSX-86: Graphics for the APe
9-8
INTERRUPT VECTORS
CP/M-86
GDOS
GIOS
AVAILABLE
MEMORY
GSX-86
Figure 9-1 GSX-86 Memory Map
The
memory required by the GDOS is less than 3K bytes. This is allocated when the
GRAPHICS command is executed. Space for the default device driver, the first
driver in the Assignment Table, is also allocated at this time. The GDOS dynami-
cally loads a specific device driver when requested
by the application program,
overlaying the previous driver. This technique minimizes memory size requirements
since only one driver is resident in memory
at anyone time. In order to ensure that
the GSX-86 loader allocates sufficient memory space for all subsequent drivers, the
default driver must be the largest driver. (Use
STAT to determine the file sizes.) Ifan
attempt is made to load a driver larger than the default driver, GSX-86 returns an
error to the caller, and does not load the new driver.
THE GRAPHICS DEVICE OPERATING SYSTEM (GDOS)
This section describes the Graphics Device Operating System (GDOS) in detail,
including
GDOS functions, the GDOS calling sequence, and how device drivers are
loaded.
GDOS performs three functions during the execution of a graphics application
proglam:
• responds to graphics interrupt requests,
• loads device drivers as required,
• converts normalized coordinates to device coordinates.