Re: Addressing 2GS slots with Orca Pascal?

[dempson@actrix.gen.nz (David Empson)]

Yves McDonald <""yves.mcdonald\"@NO SPAM sympatico.ca> wrote:

> The TMS9918A is a CRT controller chip which has text and 16 colors 
> graphic capabilities. The controller can manage up to 16 Kb of dynamic
> RAM and outputs NTSC video signal.  The chip has even an NTSC composite
> input and sync to it, making it possible to cascade controllers or 
> another video source.  Graphics are created by defining 8x8 or 16x16 
> pixel arrays and positionning them on a 192x256 pixel plane.  The small
> pixel arrays are called sprites and up to 32 sprites can be defined. 

[circa 1982, etc.]

Ah, right.  I get it now.  I was aware of these old sprite-based video
systems, but thought this might be something more modern.

As far as software support goes, it isn't feasible to integrate this
into the IIgs GUI, but depending on the complexity of the
interface/protocol, it might be reasonable to write a GS/OS character
device driver to talk to the chip.  This would alllow an application to
deal with a more convenient and safer interface than having to poke the
chip directly.

This assumes that most aspects of the controlling the display can be
represented by a simple data stream from the controlling application
(like writing to a serial port).  The driver can also provide extra
control calls for special functions (such as defining sprites).

If the concept of a simple data stream to control the image isn't
appropriate, then another option would be to write a "user toolset" that
provides a toolbox-style call interface which issue specific commands to
the chip, with data supplied by the application.

A related option would be to create a simple library which can be linked
into an ORCA/Pascal, ORCA/C or ORCA/M (assembler) application, but this
would be less flexible than a user toolset, because it limits your
choice of development environments for using the library.

-- 
David Empson
dempson@actrix.gen.nz