Nerdy Texts of Analog and Embedded Systems Wizardry

Getting the PS2 data to playback correctly took some doing. The first problem was getting the controller synced to the PS2, which was necessary to handle the configuration streams. “Modern” Ps2 controllers can be set up in lots of different ways — as a standard digital controller or all flavors of analog. You can tell them (if you’re a PS2 or l33t haXX0r) to send stick data, analog button pressure, to configure the vibration motor in different ways, etc etc. So, when the PS2 does this, our doppleganger controller has to respond correctly. The big PITA there is that the PS2 will send any number of “don’t care” digital reads before this happens. In the terminal above I’m counting polls before we switch over to analog and begin a pre-determined configuration routine which is similar from game to game.

The next problem was buffer overflow. I used to use these fancy Atmel Dataflash AT45DB642D parts to record data, and they ruled. They had onboard RAM buffers and generally took care of erasing and writing flash memory at the same time. Then every distributor ran out of them. [2011-07-06T12:42:33+00:00 — they’ve been back for awhile now, thankfully] So I made a daughterboard and used a “peoples’ flash memory” IC by SST. It was a lot more like “normal” [read: annoying] flash in that you had to handle buffering and sector erasing yourself and it was painfully slow. This coupled with the fact that when this one bowling game used the analog button pressure (O GOD WHY?) the controller was spitting like 20 bytes a read led to trouble. Specifically, I needed to buffer all the data coming off the controller while the erase happened and that could take seconds. I ended up with a 3-way ping-ponged buffer AND compressing the data so that it would only log CHANGES in controller readings. This did the trick. I felt smug.

Here’s the pretty pretty result:

So I’ve been building a bunch of video game controller controllers (game TiVos we call them) for Cory Arcangel for a big Barbican show. It’s pretty much everything from the Odyssey / Atari 2600 to the PS2. Basically, their job is to play back (repeat) a played video game in an artsy way, and to talk to a host computer for file transfer, etc etc. Most of them work by snooping the active-low buttons during the recording, then pulling those buttons low during playback at the right time. There is NO WAY this stays in sync with the system, but that kinda wasn’t the point.

However, it turns out for the PS2, that some of the bowling (yes, bowling) games Cory wanted used the ANALOG BUTTON PRESSURE coming off the controller. I was already an advocate of reading and replaying the serial stream from the controller rather than messing with the switches, but it turns out to do these games you pretty much have to do that. So, here I am, learning PS2 serial protocol. There are tons of notes online on this, but I especially liked and used Andrew McCubbins’ “PSXCONT” notes (though I couldn’t find his source code). The UPCB project, as usual during this video game project, was very helpful. Micah Dowty’s notes were really helpful. Lastly, the curious inventor PS2 site rules.

There had to be a lot of bus turnaround kind of thing to both read and playback the PS2 stream, so I needed an external MUX which I made from a 74HC157.

Armed with all that, I hooked up the TiVo, wrote some test code, let her rip, and watched the serial stream for boo-boos using the Saleae Logic analyzer.

There were lots, and they had to do with non-deterministic boot times and the initialization sequence it takes to convince the PS2 that the controller is legit. More later.