Most of us know what the Atari 2600 looks like.

But what does it's execution look like?

And why might someone want to see what it's execution looks like?

Well, for one, the 2600 is painful to program. Really painful to program.
So, for those individuals with an interest in writing games for it, anything
that helps understand how the system works is going to be useful.
And yes, there are people still writing Atari 2600 games.

While I can make no claims to the objective utility of the current tool I've written,
I have shown it to old school Atari programmers that have found it to reveal
things about the hardware that they hadn't before considered.

The work shown here is a first pass implementation, to be modified as I see fit.

I modified the Stella Atari 2600 emulator source to provide me with various types
of visual information, subsequently displayed alongside the running emulation.

Here's an example:

                         

The image above is a snapshot of the active execution of the Atari 2600 game
Pitfall. As the Atari 2600 reads data from the Pitfall cartridge (ROM data), the
location of the read is displayed visually.

As it turns out, the Atari 2600 reads some ROM data often (nearly every frame
update). To represent the relationship between frequently read and seldom
read ROM visually, two colors were used. When data is read from ROM, the read
frequency is monitored, which, when high, displays as the color blue. The seldom
read data is displayed in red, and unread data remains black. In addition to these
color differences, for seldom read data, the amount of red displayed represents
how recently the data was read by the Atari 2600. This allows the viewer to
visualize the direction of data reads as well.

The end result is a dynamic display of data reads by the Atari 2600 as a game is
played. The visuals throb with the display of each frame, producing what could be
called the heartbeat of the Atari 2600.

In addition to this data, other types of data are able to be visualized as well. For
example, register reads and writes to the TIA (Television Interface Adaptor)
component of the 2600 can be displayed, along with the static ROM cartridge data.

Click on the following thumbnails for screen captures of these data sets for different
Atari 2600 games (all of which I do own). ROM data is in grey, and TIA reads and
writes are displayed in blue and green, respectively.

Or if you prefer, take a look at a highly compressed video.