I know just about where the logic is going wrong, but not yet why. I added some more diagnostic output from the fpga board and set up for testing. I wanted to see either the output data word being loaded into the serializer or the running checksum.
I can see the two correct words of the first record being written out (both 0x0000) and the running checksum is correct through these as well. It is when the logic shifts to write out the checksum that I find the value going awry. This points me right at the logic where I transition from having written the last data word and set up the checksum as the output word.
I also looked to check the data words being written out for the second (label) record and the beginning of the third (data) record. Everything was correct - the preamble and postamble, the sync word, and the contents of those records matched exactly the cartridge image I had downloaded into the fpga board.
This leaves only the checksum to resolve and I should be able to write a cartridge image with my tool and boot it on a real Alto. I hope I can nail this before I leave for my visit to the east coast, where a few of the 1401 restoration team will visit with the Center for Tech Innovation (TechWorks) in Binghamton and share ideas as they restore their 1440, 1401 and raft of peripherals.
IBM 1130 DISPLAY PANEL UPGRADE
I have begun building all the plug-in incandescent lamp units, soldering mini bulbs to a 2 pin header that fits into the sockets which will be on my PCBs. I had hoped to have enough mini bulbs to avoid any of the regular sized bulbs from the existing panel, since these have relatively tight clearances in the honeycomb blocks.
Once I looked over my inventory of bulbs, however, I found that I only had about half the quantity I need. I did find a source for a couple hundred mini bulbs of the type I need, which should be shipped from China and arrive in mid June when I am assembling the panel boards.
I have about 40 more mini bulbs on hand, which I can solder onto headers in advance of receiving the shipment from China. This would allow me to stock one or both of the smaller PCBs and do testing even if the new bulbs haven't arrived.