Gregory's Serverok so i unplugged the board and powered up the computer -- and the error stays. looks like i broke something. 😩
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 ok when *not* in reset, the FPGA is pulling the DMA line BURST_L low constantly. this is bad, and explains the 00011320 error i saw earlier. seems that i typo'd the wiring between the top level verilog module and the module that handles the micro channel bus. it's a floating connection and it seems to mostly just sit at a logic 0. yes, i made a dedicated interposer/extender board just to help with the logic analyzer connections. it's called the Fing Longer (a reference to Futurama). hmm, so during a read operation, the data is never driven onto the bus (the output stays pulled up to FFFF). looks like the MADE24 line is staying low? that's weird. let me try making the logic ignore it.  i'll need to figure out what is up with the MADE24 line. could be that the pin doesn't actually do that. the HDD pinout is one that i reverse engineered a while back, so it might be a mistake. this could also explain the damage to the PC, perhaps the card tried to write to the data bus when it was not supposed to and damaged the output drivers of some other chip. got the Teensy interface up and running. i'm using direct IO port access on the Teensy 4.1. take a look at core_pins.h in the Teensy header files. basically you can read from GPIOx_PSR and write to GPIOx_DR. i also had to add a short delay to create some setup time for the FPGA--the Teensy 4.1 is a hair too fast lol  Great progress! But help out simpleton me, I've lost track of what you are doing. Is this still part of reverse engineering things to get a SnarkBarker to work on the expansion port?? Or an entirely different project? @darryl_ramm it is a solid state replacement HDD that works with the weird IBM DBA-ESDI protocol (similar in concept to IDE) @tubetime Cool, I would love to get a 701 butterfly. Had one for years at work.  @tubetime I’ve always wondered about that. I think your intuition is accurate since that would allow a smaller package size from less area outside the die needed to route to the external pads.   Meme image: good news bad news.jpg I have mainly reverse engineered things with user interfaces, so there’s always strings I can work backwards from. Doing something like a hard drive controller is playing the game on extra hard mode. so last night I identified the power on self test routines by inspection. it's not too hard to identify a checksum routine or a memory test routine. this helped me fill in the memory map. also, the POR test function stores the results at a particular memory location, and the codes match up with the POR error codes in the DBA-ESDI spec! the next step is to search the whole ROM for any instructions that read this memory location--this should identify the functions that generate the status block. @tubetime Out of curiosity, does the newer IBM BIOS have any similarity to the original IBM PC AT BIOS that they published in the AT Tech Reference from March 1984? Wondering if they ever did a full rewrite at some point. http://bitsavers.trailing-edge.com/pdf/ibm/pc/at/1502494_PC_AT_Technical_Reference_Mar84.pdf    @tubetime A lot of early quad SMD packages numbered starting in the middle of the "top" side, and that was purely a (dumb) thing done by package vendors, and dice were always still mounted orthogonally. (or perhaps _almost_ always) @tubetime Isn't MADE24 supposed to stay low for another four and a half months? @tubetime Is that photo from an Agilent scope screen? If yes, which scope are you using? @tubetime Ah, a dedicated 68 channel 350MHz state logic analyser. "state data rates up to 1.4 Gb/s". Looks cool expensive. Can't even find a price online. My Saleae is far away from that. @tubetime how did you get past it, if the computer's hardware is now borked? |
gotta take this step by step. I should have checked this at the start but first I will force the FPGA into the unprogrammed state (-CRESET low) then check each pin to make sure it's in a valid state.