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". ;) )

1 comment:

  1. ... and I'll have more to say on this shortly. I've given up and gone to a CPLD+Parallel Flash design...