Thursday, February 22, 2024

Saving Apollo By Decoding Core Rope

Certainly one of our favourite retro {hardware} fanatics, [CuriousMarc], is again with the excellent story of preserving Apollo Program software program, and constructing a core rope reader from scratch to do it. We’ve talked about [Marc]’s earlier efforts to get actual Apollo {hardware} working once more, and one of many by-products of this effort was recovering the contents of the read-only core rope reminiscence modules that had been a part of that {hardware}.

The time lastly got here at hand the now-working Apollo steering laptop again to its proprietor, which left the staff with none {hardware} to learn core rope modules. However the archive of software program from this system was nonetheless incomplete, and there have been extra modules to attempt to get well. So, the wizardly [Mike Stewart] simply determined to roll up his sleeves and construct his personal reader. Which didn’t truly work as anticipated the primary time.

And this leads us into considered one of [Marc]’s elevator music explainers, the place he provides a phenomenal rundown on how core rope works. And if you’re considering of core reminiscence based mostly on ferrite cores, prepare for a mind stretch, as core rope is sort of a bit totally different, and is much more difficult to learn. Which brings us to the bug in [Mike]’s reader, which is definitely a bug within the block II design of the core rope modules.

Studying a byte off the module requires setting a number of inhibit wires to pick out a person core. An innovation in block II allowed these inhibit wires to run at half present, but it surely seems that didn’t truly work as supposed, and partially chosen a number of cores on the opposite half of the module. And [Mike] neglect to re-implement that bug — the reader must actually be bug-for-bug suitable. A fast recompile of the FPGA code makes every little thing work once more. And the conservation effort can proceed. Keep tuned for extra within the Apollo story!

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