Tuesday, November 7, 2017

Investigation continues...

I went through and verified the pinout of the cart, and burned a new AVR and dropped it on the board to test, but it's still working just as flakey. A couple of things were interesting.. one is that when it partially works, it seems to get most of the bytes right (because the program selection is mostly correct). That seems to suggest either I am lucky or the address code is working. (I suspect the latter - if I was lucky I wouldn't be having an issue).

Putting the logic analyzer on it was all over the place, to the point where I couldn't make sense of what I was seeing. But I also determined that my console's power switch is wearing out... so I need to make a repair there to continue anyway.

One thing that has crossed my mind is that with the new compiler, the code may be running too fast. I check the MDIR and MODE pins immediately after detecting GSEL -- maybe that's too fast? When I get the logic analyzer properly on the bus I will recheck that theory.

This shouldn't even be an issue, but I am leaning back towards the ROM-based cart.... I just want this part to work. ;) But in the meantime, I relaid-out the cart to use the ATTINY861 instead - it's a 20 pin part instead of 14. So it doesn't look as much like a GROM, but it has enough pins to bring out the ISP header. I also positioned it so, in theory, the ZIF socket will fit on the board when in the console. I haven't ordered this board or the new parts yet though...

I probably should test programming one of the 128MB flash chips as well -- if my new programmer can pull that off, maybe I should stop wasting my time with the GROM emulation. (But darn it, this part was supposed to "just work". ;) )


Saturday, November 4, 2017

Didn't Work First Try

Never should expect that it will, but I'm a bit disappointed and frustrated at this point.

I had two things to do today - the first was to port my GROM simulation code to the ATTINY84 that I selected for GROM boot. I thought it would be nice to have that to startup, and I could use the EEPROM for high score saving.

That port went reasonably well, and for the most part it did what I expected. Then I shut off the reset pin and discovered that I don't seem to be able to get high voltage serial programming, needed to reprogram it without a reset pin, to work. I spent several hours on this, including research and rewiring it repeatedly. I seem to recall having this issue before and eventually deciding keeping a reset pin was a good idea, but I need every I/O an ATTINY84 has. I think I may nudge up to the next physical size.

Then I went to build the cartridge prototype, and pretty much everything on that PCB was problematic.

First I detected that I didn't actually buy all the ICs I needed to assemble it. I was able to raid the parts bin but it was frustrating. Then, of course, the ATTINY footprint was too close to the IDE port to allow a ZIF socket (I always forget how big they are), and I forgot that the pins need to be larger.

I soldered leads to the ZIF socket to get it on the board, and forgot you need to do that when it's OPEN, not closed, because otherwise the sockets don't always open up for you. ;)

Finally, I got it all together and plugged it into the TI. It didn't come up reliably, it's very flakey, but at this point I think I'm done for the day. When it did come up, the data was correct. I got as far as seeing the menu entries and even getting Easy Bug to start booting, so the basics are working. Either there's some timing issue or I configured one of the I/Os wrong, or (worst case) the IDE circuitry is interfering.

Because I was too dumb to test it before I put the IDE circuitry on.

So I think the next step is to take Jim up on his layout offer while choosing a new chip for this approach, and we'll see which layout works first. ;)


Also did a few surveys to see what people thought about dither patterns. My first favorite was shot down pretty hard, but in the second pass there are two contenders neck in neck, one of which IS my favorite. Sadly there are only about a dozen votes, which speaks lovely for the potential market of this thing. Oh well. ;)

So it looks like we'll be using an ordered dither, but in order to get around the terribly washed-out effect I was getting, I introduced back in a tiny bit of error distribution. It makes a difference in the color yet preserves the more regular patterns of the ordered dither, and I'm pleased that people like it. It's really down to whether I'll use the 2x2 or the 4x4 pattern at this point. (When I re-encoded, I'll probably just do the top four so I can change it out again at the last minute without fearing that the frame numbers might change...)

You can see the current challenge video here (if you can get past Youtube's scaling...): https://www.youtube.com/watch?v=NdO-lokD7DM

Thursday, October 5, 2017

I think it'll work...

I have laid out an IDE interface with an UberGROM powered by an ATTINY84 - that'll give me 8k of GROM on the cart, which is plenty to bootstrap and maybe even run the game.

I'm expecting to need 32k to run, but I guess we'll see.

Anyway, I've still got a long way to go.. hopefully using this will let me work out the kinks and prove the hardware and software both. My first pass, I'm just going to load EasyBug on the GROM so that I can poke at the CF card manually.

I was silly and laid out the PCB before getting the TI cart outline, so I made it way too tall. Still, I think there's a good chance it'll fit. One more night should be enough to get me there... then I can order some and we'll see.

Monday, October 2, 2017

Dragon's Lair Initiated

Honestly it was initiated a long time ago - I have been building the tools for this project literally for decades, and got the license six months ago (that's a badness on my part too, but it's not too late yet!)

I posted the proof of concept on YouTube back in May 2015: https://www.youtube.com/watch?v=iOFPusM2dtM

I didn't have a lot of free time to work on it since then, but since the software was proven feasible (and all the video encoded and spliced out), I worked loosely on getting the license. I finally got ahold of someone at ReadySoft who okayed me and paid for that, giving me a year to get the thing done and out there.

Of course, in typical me fashion, I worked on other things. Sigh.

But this is now top priority with six months to go, and the last unknown is the hardware.

I actually thought I had this more or less nailed down... I found some nice 128MB flash chips in China, and they're still available. With that, some voltage conversion, and a dumb and simple banking scheme, I should have enough memory to store the 16 thousand 8k banks that I'll need. And this is still true! But the bummer with this scheme is that I've never really known how I was going to program the damn chips.

As I sat down and started sketching out the board, I began considering alternatives again, and I found myself wondering "why not compact flash?" It's 5v compatible, comes in huge sizes for low-ish cost (better than the flash chips anyway), and is easy to program.

I spent some time studying the datasheets and couldn't see a why not. The worst case minimum cycle type at the slowest speed is 600ns. The TI memory cycle is 667ns. So why not? I embarked to find out.

There are a few why nots... one is that the card automatically goes to sleep, and is rated to take 20ms to wake up for a read. That's a pretty long time, and my video playback needs the fastest cycle time possible. But if I can wake it up for a scene and keep it awake until the scene ends, then that should be okay. I can read multiple sectors in one command. Feasible!

Of course, then I needed to check sector size versus data size. My video frames, which interleave audio, are 7686 bytes in size. Can you see what's coming? That doesn't line up nicely with 512 byte sectors. In fact, it's 6 bytes over the size of 15 sectors. That's pretty annoying. I haven't done this yet, but I'm going to try and hide those six missing bytes by duplicating bytes in the color table. ;)

I then got obsessed with using memory mode, and not IDE mode. I bought some CF to IDE adapters and worked out how to mod them not to come up in IDE mode. I then tried to map it all down to a RAM chip on the mini-memory cartridge, and mapped it into that space.

My first attempt came up but didn't return anything... I realized that I'd attached to the RAM chip's (disconnected) CS. I fixed that, and the console won't even start up with it inserted. Well, that figures.

At this point, troubleshooting with the MiniMemory in the way feels very complicated... so I'm going to just lay out a PCB with an uberGROM (so I can still use EasyBug) and let the CF interface have the entire ROM space - that will give me a lot of flexibility in how I talk to it. It will also let me add the circuitry so that it responds only to even addresses, so that I don't need to worry about whether double accesses break it (something I couldn't guarantee with MiniMemory). Downside, it will cost me time, maybe a lot, to get the PCBs made. Chicago's in two weeks? Yeah, that's not going to work.

I didn't need to present anyway. ;) I guess I can announce it and show a mockup on the PC. Nobody really did much with it at FestWest.


Saturday, September 23, 2017

Why So Serious?

I haven't posted here for a while... the main reason for that is I've just been busy on non-code-related projects, so I didn't have much to say here. Sure, I could post the odd rant like I used to, but let's face it, those were for me. And I only posted the stuff that was tame enough to not scare the children.

I've been programming for a long time. By long I mean "damn long". It's true I'm not one of those old mainframe-y types (stop fixing my spelling Blogger. If I don't want to use a hyphen, that's my right!)... but I started with TI BASIC back in 1983 and barely a day has gone by that I haven't done SOME kind of code.

To me, of course, 1983 must have only been like 17 years ago, cause time stopped at 2000, didn't it? But when you do the actual math and realize it's actually been 34 years, then yeah, I'm going to start accepting the scale of "damn long".

No, I'm serious. It's a weird phenomenon. To me (and I've seen posts from others with a similar viewpoint), 30 years ago still means 1970. So it's weird. Time stopped in 2000.

There /is/ a thought that's sticking in my craw and needs to be written out, but in truth I haven't figured out how to say it nicely enough yet... let alone what solutions to offer. So there's no article there.

But... you can expect this blog to slowly re-awaken. The non-computer stuff got done and my next task is the development of the Dragon's Lair cartridge for the TI-99/4A. This is a full-motion video and audio production of the classic laserdisc, running on authentic hardware. The proofs of concept were good, now I need to actually build the hardware. Hoping to have something by Christmas, but watch this space, since it's as good a space as any. (If it'll stop being picky on my spelling...)

For after that, I have a huge list of things I want/need/obsess to do, and rather than be picky, I decided to crowdsource the decision. I considered kickstarter and such, but if you give me money then I'm obligated. So instead I went for SurveyMonkey. If you have 3 minutes (the average completion time), do me a favor and go click what looks most interesting to you. I think I get up to 100 responses for free or something.

https://www.surveymonkey.com/r/8CJDR5C

Thanks for that! Or if you don't, thanks for nothing! Either way you get some kind of thanks!