It seems likely to just be z80+stm32 - less parts, less complexity for people to hack on, but without reducing the function, and still retro goodness. I rather like the idea of z80 and stm32 -- so the z80 can drive it all, or you can just do stm32 if you want a beefier approach and less retro. Hell, use the z80 for doing sound or something then..
Especially with the STM32 F4 at say 168Mhz (or the latest one, at 180Mhz).. thats crazy. But I'll find out, first ..
The AVRs are really good at some things; with the fact almost every opcode is a single cycle, and predictable, they can actually work pretty nice; you can just make a tight loop to spit out VGA, and .. they can't keep up, but the pixels they render and square and lined up. On the ARM chips with complex caching and pipelining etc, its much harder to get timing right, so you have to go hardcore with the peripherals and timers, and its not as efficient; but less efficient, with 8+ times the performance is something
Basic VGA is pretty easy to get going, but its still blurry and goofy; I know it can work solid, and can just move on.. but I think I'd liek to get a sharp high res VGA proven (and hey, its painful/fun..), before I start finalizing the design. Don't wan tot go ahead, nail things down, get boards made, and find out its just not going to work the way I want it to. So I'll spend a couple weeks banging out a cleaner tighter VGA, and then can test if the interupts can come in nicely a few ways without blowing up the display. Theres performance to spare, so generating audio right in the STM32 (and ignoring the AY-3-8910) should be doable .. run a SID emulator or whatever.. but the interupts, they're what get you. Keyboard interupts aren't as frequent (they did shoe on the avr8 generated VGA, but probably not here too much, since we'll be doing 600 or 800 60hz), but if its monitoring the z80 bus (say), or i2c, or such like that.. you have to answeer or miss the data; dont' want the z80, if we let it run at say 20MHz or something, to just blow up the VGA. Thats the test I need to do before we start nailing the pcb out and shipping it to the boardhouse.
I really like the avr's (ordered a few more, so I have 'em 'in stock' for my projects), but if I can trim a chip out, a different family chip, I'll do it.. the goal here is retro styled, but still simple and fun. If its not simple, I can just pull out the Big Crazy zikzak board; the point is to reduce, but still keep the retro flavour for fun coding, and keep complexity down so idiots like me can figure it out.
I don't sleep enough for these hard-timing games; its hard to get right. I bet its way easier if I had a few days of rest... such is life
I did break down and pick up an STM32F4 discovery board with a F429 on it; $27 or something, including an LCD display I'll never use, and 2 usb ports; its got all the pins broken out onto headers, has the crystal and st link v2 built in, etc. Pretty amazing for the price of the board, and it doubles as a st link v2 programmer (which alone costs like $40.) So it can program its own F4, or program other chips.. break a jumper and its a programmer, put jumper back and its a standalone board. I like to do it from scratch, its not too hard to just have a single chip on the breadboard, but I got lazy here.. plug it in, get to work. Could be an option for you.. its got the crystal on board, so you can hit it up to 180mhz right off and go, and certainly pretty cheap.
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FWIW, I get all my gear from ebay and much of it comes from HK or China; I almost feel bad for stiffing the local shops, but there aren't many.. and the few shops around are basicly carrying stuff from China anyway, but marked up a few hundred percent. ITs hard to argue when ZIF sockets are $17ea here, or 10 for $5 on ebay :/ I got the microscope for $11 (absolutely essential for SMD work; get the Andonstar one with the nice stand .. its _all_ about the stand, and view distance, so you can solder under it while watching your 20" monitor. Beauty. I got the 858D hot air rework for what, $50 or something, not too shabby at all. The most expensive piece was splurging on the sucvtion desolder station, which is neat as heck, but not as useful as the hot air.. once you get the hot air going, it makes your life a lot easier, and its pretty cheap.) The tools don't ost too much, and the components are pretty cheap ebay wise .. thgouh quality suffers. digikey etc are beautiful, but you pay a lot for their amazing service. The free samples help a lot .. when mcu's are $8-$23ea, and you must be 4-5 of them in case you kill a couple .. it adds up.ST sent me 5 of the F4's .. the high end $23CDN ones .. free! That one package was abotu $100 or more value, and went straight into my prototypes.
You can get by 'cheaper', but by no means 'cheap'; you need a base stock of resistors (I bought a pack of 5000 from china, natch), capacitors (tantalum, electrolytic, mono...), the SMD adaptors (which are expensive, but I got them from thailand, egypt, all over), voltage regulators (use a heat gun, melt them off old boards
), stock of various crystals.. your basic starting lab has some costs. A good solder station is absolutely worth it.. get the Hakko 888 or 888D, beautiful. A good multimeter.. I've gotten good old stuff; I got a 20 year old MM and had it checked on a high accuracy machine, and it was still to spec.. got it cheap, and beautiful. Multiple power supply.. buy a cheapo kit and assembly yourself. I was building power sdupplies for awhile with the 7805 regulator etc, but got tired of it.. when you need 3.3V on some chips, 5V on others, and using buffers to level things.. bleh, just get your bench power supply to spit out 3V and 5V at once, call it a day. Its all about optimizing what little time you have, for me.
And now I have a _wicked_ office .. full of neat toys, mostly cheap but awesome. Think ahead.. when you get a 858D hot air station, how you going to get that 350 degree chip off the board? I tape the board down, and tweesers iwll burn your fingers! I was using an oven mitten, but its too fat-finger. Get a $2 suction cup pen from ebay.. garbage, but good enough, and disposable if you melt it. So far so good for me
Nothing worse than buying a gadget on ebay, only to find out its runs at 220V and you run at 120V, or you need a sucker pen, or _something_, and you need to wait 6 more weeks for the next thing from China
Plan your lab, get it cheapo on ebay, and get hacking
Love them freebies
