Atari & VHDL
Purpose of this page
To improve awarness to the various projects and the collaboration of ideas.
What is VHDL and FPGAs
An FPGA is essentially a semiconductor with blocks of logic gates that are ready to be connected together to create functions. It's commonly programmed with a language called VHDL, (Very high speed Hardware Descriptice Language)
Whats so great about it
The FPGA is free to be wired up inside exactly how you wish. By using combinations of logic gates, lock up tables and internal ram, old obsolete chips can be re-created. For example, the Motorola 68000 CPU could be recreated inside an FPGA, and due to modern construction techniques of silicon, clock it faster than the 8MHz standard speed.
Even if a bug is found in the logic, the chip can be reprogrammed with an updated firmware. Also, errors or shortcomings in the original designs can be fixed or modified. Extra interfaces can be added very easily.
Applications of programmable logic on Ataris
Since the late 80s and early 90s small amounts of programmable logic have been used in Ataris. The Falcon featured a set of GALs to help the 68030 processor interface to the Falcons buses. Most recently we've seen CPLDs being used on the CT2 and CT60. The SuperVidel is a great example of the use of FPGAs. Here, a VIDEL is recreated into an FPGA, using idetical register sets yet allowing for a much higher memory bandwidth. This maintains compatibility, but increases speed.
So far it's not certain how much can be achieved, but here are a few ideas.
A whole Atari ST in a single chip
There is some work going on to recreating the Atari custom chips into VHDL language.