Tube Time

@TubeTimeUS

vacuum tubes, vintage computers, the MOnSter6502, cross-sectioned electronic parts, memes, and other detritus. BNC stands for Baby Neill Constant.

Silly Valley
tubetime.us
Joined May 2011
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  1. Pinned Tweet
    15 May 2016

    so i made a thing. a very big PCB with 4304 components. A 6502 microprocessor.

    65 replies 577 retweets 1,788 likes
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  2. 20 hours ago

    there's a bit more rework now. this is for adding separate sync outputs for the VGA connector. the buffer is a 74hct125 which also replaces the two transistors.

    2 replies 3 retweets 48 likes
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  3. Apr 20

    well here is a good-looking machine! i really dig the aesthetic.

    0:30
    A Turing machine is a math concept that show that a few simple rules can be used to solve any computable computation. Mike Davey built this model embodying the classic look of the machine presented by Alan Turing in 1937 [video: , ]
    13 retweets 79 likes
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  4. Apr 19

    the Gremlin now supports FPGA multiboot! there are 3 bitstreams selectable by the top two DIP switches: MDA (classic 18KHz hsync), MDA (31.7KHz VGA), and CGA (31.7KHz VGA output with simultaneous 31.7/15.7 coming soon)

    3 replies 1 retweet 48 likes
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  5. Apr 19

    much better! i also had to extend the ISA bus operation mask by one cycle so that ISA bus operations don't step on that last cycle. this manifested as occasional write data corruption.

    1 reply 22 likes
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  6. Apr 19

    here's the problem: vram_read needs to stay active for another clock cycle to make sure there is enough time to read the data. (see red line below)

    1 reply 20 likes
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  7. Apr 19

    welp, MDA broke while I was busy with CGA. classic timing issue while getting the attribute byte. it's marginal which is why it worked before.

    3 replies 20 likes
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  8. Retweeted
    Apr 19

    A look inside a 2N2222A transistor in a TO-18 metal can package. The transistor die is a little cuboid block of silicon. It's connected with wire bonds to the two insulated pins, and through the cases to the third pin. Outtake from a photo shoot with

    10 replies 133 retweets 695 likes
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  9. Retweeted
    Apr 18

    Cross section of a compact power fuse. It's normally filled with sand, which (1) supports the element against vibration and sag, (2) provides "slow blow" thermal mass that allows it to withstand transients, and (3) suppresses arcs. Outtake from a photo shoot with

    7 replies 15 retweets 101 likes
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  10. Apr 18

    i mean it *looks* kinda like an MBR. first half has the bootloader code, second half has the partition table. but it doesn't end with 55 AA.

    4 replies 15 likes
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  11. Apr 18

    lets look at the first sector on the disk. it almost looks like real data, but something's not right.

    2 replies 27 likes
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  12. Apr 18

    wrote some crappy python to decode the sector header. the index mark uses flag 4 and sector 13. sectors are marked 1-25, with the 26th named 30, for some reason.

    2 replies 26 likes
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  13. Apr 18

    ok made some great progress by reading multiple tracks. track# is a 9 bit field but the bits are inverted. track# also uses two LSBs of the A4 address mark.

    1 reply 23 likes
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  14. Apr 18

    got a bit more decoded by reading data from several different heads. last 16 bits are probably the header CRC. next, i need to figure out the cylinder/track number. since the drive has 1224 of these i'll need at least an 11 bit field.

    4 replies 1 retweet 34 likes
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  15. Apr 17

    if i stare at this long enough, i'll start seeing patterns. i think the sectors are interleaved but the rightmost field could be the sector number.

    6 replies 50 likes
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  16. Apr 17

    shortened the sync a bit and noticed some repetition (since the logic analyzer captured a bit more than a single rotation of the disk.) there appear to be 27 of these. this corresponds with 26 RLL data sectors and an index mark.

    1 reply 25 likes
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  17. Apr 17

    possible sector headers.

    2 replies 27 likes
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  18. Apr 17

    this seems to be an easier way to look at the raw RLL data. each number represents the number of zeros in between the ones. the start of a sector header seems to be 3333423333.

    3 replies 26 likes
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  19. Apr 17

    so two nearby sectors look like this. i think the highlighted bits are the sector header. the actual sector data itself seems to be the same for both sectors. the sector header should contain the sector number, track number, and head number

    1 reply 1 retweet 21 likes
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  20. Apr 17

    the gap between sectors seems to be filled with this pattern: 1000100010001... depending on your starting alignment, this can decode to a long string of '11111111111...' or '1010101010101...'

    2 replies 28 likes
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  21. Apr 16

    fixed a bug in the decoder, and now i see this

    4 replies 59 likes
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