Madeleine: My second PCB layout - Page 1
Forum section: electronics / projects

author: Godzil
author_rank: Frequent Contributor
timestamp: August 22, 2015, 01:25:24 pm
content: As I explained in my presentation, one of my hobbies is related to retro-computing and old gaming consoles, and the one I'm working with currently is an old Japanese handled console (old, the original model was out in 1998, the latest in 2003 it's not that old in fact..) and even if there is an official development cart that was sold, it have a lots of limitation (especially about size) and it wasn't possible apart from taking an existing game and replace the actual ROM to build a custom cart if you want to make your own game on it.During the last two years I was slowly working on reverse engineering the official cart, especially the "protection mechanism" (which is more a way to check that the cart connector is clean and correctly inserted than a real copy protection) and decided to build a real development related cart using none of the original components (and that have the same size as the original cartridges)As this is quite a big project, I cut the cart design in two part and design goal, the first step would be to create a simple, but working cart that use NOR flash for storage, and a CPLD as glue logic, the second step will be to use SRAM+SD for ROM storage and a FGPA as glue logic.The reason was also because as the cart is really small (there is room for component on only one side and the PCB is about 61 x 30 mm with a large part taken by the edge connector (about ? of the board) the FPGA because of the number of connection would need to be a BGA one.Anyway, i wanted to share here the layout of the PCB I've build to have your though on it, if you see any flaw or thing that could be donne better, as it is my second design (it has been hand routed, I only use auto-router to see if the board seems doable or not)The component placement is not optimum around the CPLD for the decoupling caps, but with all the signals and size constraint that it wasn't easy to do the placement.This is close to the final design, the only change to be done is on the 1mm connector that will be replace by an easier one to use for the end user, but will be unfortunately more expensive, and the two placement holes are a bit off.Anyway, please fell free to comment the designHo, and the design has been done using Kicad with the latest version, using the new router with push and shove (it helps a lot on such packed design, even if I needed to reworks a lot of things after to get things nicer to the eyes)

author: bson
author_rank: Unknown
timestamp: August 22, 2015, 08:46:20 pm
content: If you do go FPGA and bite the BGA bullet I'd just put everything in it: ROM, SRAM, and a small uC with a USB interface.

author: Godzil
author_rank: Frequent Contributor
timestamp: August 22, 2015, 10:21:27 pm
content: The BGA FPGA will be used on the next step, but ROM is not needed, USB I still don't know as a SD card is a good trade on universality.Tthey are easy to plug on a PC, load data inside and put them back on the card, but if I put a FPGA, the uC of ROM will clearly be not useful, the uC would be part of the FPGA design, and the ROM will be simulated using the (big) SRAM on the cart. The problem with a NOR is it's whole life, as each time we will change the content we loose a cycle.SRAM is much more suited for that, as the logic around would make sure that if there is any save data not backup it will not be loss.But that for sure that this board will be loaded with lots of bonus (like accelerometer or other fun stuff like that) but that's another part of the project, and clearly not fixed for now, I still have a few problem to fix before, like getting better skill on BGA soldering, my last attends was.. a failure..