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Top-level
 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 146 comments
 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 I've lost count of the things I've done that "sounds easy but the process uses DMA."  @tubetime @tubetime Almost makes you want to lovingly caress it's slightly sticky chemically degraded surface. 😉   The logic analyzer from the perspective of the PCB: https://www.youtube.com/watch?v=nYPX-QQR9Tg @tubetime it’s been so long since this experiment started I forget what you’re trying to do! @tubetime @tubetime I implemented PS/2 DMA in an emulator good enough to get a Sound Blaster working a while ago and god help us all @luigithirty nice, you didn't even have to get burst mode working 😉   @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) |
Gregory's Server
bidirectional registers now work! i can write a command from the PC to the Teensy, and i can write a response from the Teensy and read it from the PC. there are also status flags showing when new data is available. it may not seem like much, but this is huge progress.