tubetime

tubetime, 10 days ago

it would be nice to be able to repair the logic boards. a schematic exists, which is quite helpful.

tubetime, 10 days ago

what's interesting is that the board hosts a microcontroller. the schematic lists it as a "6510" which makes me think it is 6502-based.

tubetime, 10 days ago

on my board this is the part marked 80118-501
R1512-11

and it has the Rockwell logo, making me think it is something from their R6500 series of 6502-compatible microcontrollers.

tubetime, 10 days ago

another version of the board has the EPROM footprint populated, and the chip is marked R6518AJ, which is definitely a Rockwell microcontroller. the firmware has already been dumped.

tubetime, 10 days ago

you can find good info here: https://bitsavers.org/pdf/seagate/mfm/ST-251/

tubetime, 10 days ago

this definitely looks like 6502 code. time to pull it into Ghidra.

tubetime, 10 days ago

oh yeah. i've mapped it starting at address 0x3000 but the hardware maps the ROM chip in starting at 0x0100, where it just gets aliased all the way up to 0xFFFF. the absolute jump addresses located in the vectors at the top of the ROM refer to addresses starting at 0x3000, so i'm just using that.

tubetime, 10 days ago

hmm, looks like there are a few instructions that aren't 6502. apparently Rockwell defined a few new ones. it would be nice if Ghidra could handle those.

image/png

tubetime, 10 days ago

@fsphil confusingly, Rockwell used the same numbers for different chips. this is a different device.

tubetime, 10 days ago

@Dtl yes, find the Gesswein MFM emulator.

tubetime, 10 days ago

hmmm what's this

tubetime, 10 days ago

ahhhhh much better. thanks to whomever added R6518 support to Ghidra just now. oh wait that was me

tubetime, 10 days ago

ok so funny story, the Ghidra target of "65C02" already supports these instructions. at least i know how to customize Ghidra...

tubetime, 10 days ago

some interesting routines. this one waits for the spindle speed (as measured by the index pulses) to exceed 3593 rpm (or so).

tubetime, 10 days ago

they have a clever delay-by-x routine. the entry point is delay_entry. and yes, the routine calls its own rts as a way to insert cycles...

tubetime, 4 days ago

so one of these drives blew a tantalum capacitor. i think i will take this board apart for reverse engineering purposes. there are multiple revisions but this will be a good starting point.

image/png

tubetime, 4 days ago

with a combination of hot air and a desoldering gun, i've taken it down to just a few surface mount parts. i'm going to leave those in place for now since many of them are not marked. there is also no silkscreen.

tubetime, 4 days ago

they scanned well. i've taken the top and bottom images and lined them up precisely. these reference images are 600dpi but i may go for a lower res version for KiCad since it stores the images in the pcb file, which slows it down a lot.

tubetime, 13 days ago

in the meantime I printed up this cute little adapter so I can replace the dying hard drive.

tubetime, 13 days ago

qbasic never looked so cute!

tubetime, 12 days ago

gonna install Windows 98.

tubetime, 12 days ago

amazingly enough, the battery pack measured 9.3V, which means that at 3.1V per lithium cell, it's not totally destroyed. let's see if it holds a charge.

tubetime, 4 days ago

got the new CMOS battery, but I haven't ordered the new connector yet because I don't have enough of a list for a full Digi-Key order 😑