Lots of good news on the Tiny CPU front!

I successfully programmed a Flash ROM via the JTAG indirect method today. Woohoo! I was never able to get it to work previously, and couldn’t figure out why. Several possibilities:

Comically long, loopy wires connecting the CPLD to the Flash? These were pretty much guaranteed to act as antennas and pick up noise. I replaced them with neatly wire-wrapped connections.

Questionable software? Previously I was using a demo copy of the commercial program TopJTAG Flash Programmer. When I tried to program the Flash, it would just time out. I switched to using a free, command-line JTAG/Flash tool called UrJTAG.

Unsupported Flash type? I switched to a 512KB AM29F040B, instead of the smaller capacity AM29F010B. I’m not sure it really mattered, but the AM29F040B was specifically mentioned as a supported Flash type for UrJTAG.

Unconnected VCCIO? The CPLD demo board I bought from eBay appears to have a design flaw. The VCCIO pins are all connected to each other, but not to anything else! I only discovered that by accident. I’ve now connected them to 5V.

I changed all four things at once, and now it works. The programming speed is about 400 bytes/second. That sounds pretty horrible, but it’s actually not bad. Programming an 8K block took 22 seconds to write, and an additional 16 seconds to verify. That’s plenty fast enough, so I don’t think I need a separate bootloader.

What’s even more exciting is that I got the ship confirmation email from BatchPCB today! That’s 15 days from design submission to shipped boards, which isn’t as bad as I’d expected it to be, but it still seemed like an eternity. This is only my test PCB, though: it only has a single CPLD (Tiny CPU will have two), and no RAM or ROM. It should prove that my basic PCB design will work, though.

Progress on “making things smaller” is going well too. I got some 32-pin PLCC Flash ROMs, which can still be unsocketed and put into a stand-alone programmer if necessary, but are only about a quarter the size of a comparable DIP. Here’s a comparison:

I’m also getting more confident in my surface-mount soldering skills, to the point where I’ll probably look at replacing some of the other components like the RAM with smaller, surface mount versions. Now that I’ve got JTAG indirect programming working, I could theoretically switch to an even smaller surface mount Flash ROM package too. I’ll probably keep the PLCC version, though, so I can retain the option for stand-alone programming in an emergency.