I finally have a small amount of time to revisit the Gigatron XL.  I left it off at having problems with my PROM executing the correct code.  I first need to verify the correct commands are coming out of the PROM.  I know the code is in the PROM, but I'm concerned the bytes are swapped.  So I need to do some debug.

Second problem is the PROM are one-time-programmable, and I don't want to go through a ton of PROM chips.  So I went ahead and made the Flash cartridge board which is re-writeable.  I then needed to make a programmer for that board, so I made another board which is an Arduino shield only for the purpose of reading and writing my cartridges.  They are now both on order at https://www.pcbway.com/.  And I don't know if it's been a long time since I ordered a simple 2-layer board, but yo are they inexpensive.  On the order of $2 per board.  These prototypes would have cost me more like $100-200 per board like 6-7 years ago.  It's crazy how much the prices of bare PCBs have fallen.  The biggest cost for the Steves in the Apple 1 development was the cost of the PCBs.  Jobs sold his car to afford them.  And I'll have them in about a week, so I can continue development work soon.

Next up is writing a small piece of my own machine language code just to verify it is coming out of the PROM/Flash correctly.