Sunday, July 14


Daily News Stuff 14 July 2019

Doublesoft VGA Edition

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Tech News

  • The world's worst video card is complete!

    This was part one that sent me down this retrocomputing thought-experiment path.

    And now part two: Life's a finch.

    I love the minimalist DAC he builds.  It's not technically correct but it gets the job done.

  • Watching that video I realised that you can do something really sneaky with software-generated 64 colour video.  You're only using six of your eight bits (assuming one byte per pixel) so the two extra bits can be used to encode HSYNC and VSYNC.

    You don't need to output those on separate pins from a timer; you just need to consistently output one pixel every clock at the correct rate.  Where HSYNC is needed you output a byte with only that but high, and the same for VSYNC.

    Which would be a recipe for disaster if you were directly transmitting the bytes from the frame buffer, but my plan is to use software to create a line buffer first, and put the HSYNC/VSYNC codes in at that stage.

    Which makes my PIC32MX design that much simpler if I can solve the problem those Cornell students ran into with DMA priorities.  Though I can't simultaneously use those bits for Z-channel and H/VSYNC.

    Or...  Can I?


  • That Amiga-on-a-chip from yesterday has couple of little brothers, or possibly sisters - I can mostly decode STMicro part numbers now but I'm not sure which is the gender bit - the STM32F730 and STMF750.  (

    The former is the part used in that Black Ice MX developer board; the latter is sort of half-way between the low-end and the high-end.

    These are also Cortex M7 parts, but slower (216MHZ vs. 400MHz) and with a lot less RAM (256KB and 320KB vs about 1060KB when you add up all the banks).

    The F730 is about A$7.50 locally (qty 1).  I got the description wrong when talking about the Black Ice - it has 64KB of flash and 256KB of RAM.  These parts are designed to be used with external NOR flash, which as I mentioned costs $2.28 for 16MB qty 1, but is slower than internal flash and not great for directly executing code even though the chips can do that.

    The F730 doesn't have the video controller and blitter; but the F750 does, and comes in at A$9.74.  Unless you add external RAM though you're blitting at most 240KB of data so it won't take very long.

    16MB of 200MHz SDRAM costs a whole A$2.53 though.  If that's too steep, 8MB is A$1.81.  Or 69¢ on AliExpress as long as you buy at least 10.

    AliExpress is something of a trip.  What's this chip for $1.23?  Oh, it's a gigabit GDDR3 video RAM?  Cool.  And this one for $15?  It's a Radeon HD 4570 GPU?  And this - wait, that's a 6116, it's a 2KB static RAM chip from about 1982.  Okay, look, that's a 6502.  What did you pull that out of?

  • Speaking of the Black Ice card, the Lattice Ice40 FPGA it uses costs as little as A$2.17, again in qty 1.  It includes 14 256-byte RAM blocks, which doesn't sound like a lot because it isn't, but if you need some FIFOs or dual-ported RAM because you can't get your video timing exactly right in software, that's plenty for both a colour lookup table and a line buffer.

    I was looking at some of Lattice's other parts and it looked like Intel offered better value, because the cheapest Ice40 LP has no RAM blocks at all.  For some reason the even cheaper Ice40 UltraLite does.  The problem is it only has 26 I/Os, which is absurdly constrained.  I need 11 inputs and 12 outputs to do anything with it at all, which leaves 3 for real-world design constraints.

    So the cheapest Lattice part has too few I/Os, and the next cheapest part has no RAM at all.  It's a whole A$5.51 for a part that has enough RAM to be useful (64Kbits) and enough I/Os as well (67).

    I noticed that Intel / Altera also had some amazingly cheap FPGAs - starting about that same price - but didn't check the I/Os column.  Yep, 27 I/O pins.

    The solution if I want a simple 8-bit-style design and not an entire 16-bit Amiga-alike might be that middle chip.  If I make things sufficiently weird in software no-one will care that I'm abusing a hardware video controller to do it.

  • I also looked at free / opensource tiny real-time operating systems.  

    ChibiOS/RT caught my eye, because of the name, and because it has hardware drivers for most of the built-in devices in STMicro Arm chips.  They have a long thread on STM32H7 support - which is the Amiga-on-a-chip - and basically everything works now except Ethernet and then three months ago STMicro released updated hardware.  The two smaller chips use older, well-supported devices and work just fine with ChibiOS.  They have an updated Cortex M7 CPU, but that's basically 100% compatible; it's the I/O devices that cause the difficulties.

    Anyway, it handles stuff like providing a driver for SPI-connected NOR flash so that you can then load a FAT filesystem on top without having to spend every weekend for six months getting that stuff working yourself.

    It looks like the STM32F746VGT7 might be easiest to work with.  It has 1MB flash (so I don't need to worry about external flash) and a video controller (so I just need some resistor ladders, no external FIFOs, LUTs, or DACs).  It has 320KB of RAM (enough for an 8/32 bit system), which is broken into separate blocks but not as many as the H750.  And all the I/O devices are supported by ChibiOS.

    For that convenience though it costs $20.  But I don't need an FPGA or external flash to make it work.  Just the chip, and an oscillator to get the video frequency, and a bunch of resistors and capacitors, and a VRM, and an Ethernet PHY, and an RS-232 line driver, and whatever it is you use for USB.  And is there something that needs to go between the CPU and an SD card?  Probably not since those are passive.  NB: If this ever comes into existence and you blow it up by putting the wrong thing into the SD card slot it's not my fault.

    Update: Wait, if I'm going to build the simpler 8/32 bit version first, I don't need Ethernet anyway.  So the fact that it doesn't work in ChibiOS yet is kind of irrelevant.  I can use the cheaper H750 to do the 8/32 version (just masking off most of the RAM), and then use the exact same hardware for the 16/32 version.

    So one $40 developer board and I'm set!  Where's that Arm Thumb-2 manual?

  • I read the manual on the display controller first.  It doesn't have any way to configure it for line doubling.  As far as I can see, the only way around that is to have an interrupt on HSYNC that subtracts (for example) 320 from the address of the frame buffer for lines 1 through 5 out of each 6 so that the controller keeps trucking along not knowing it's repeating lines.  Only... Not sure if that will work at all.

    Update: Oh, the AAH register might be the key.  Stupid thing only goes up to 768 anyway.  If I decrement that on HSYNC it should send the same line again.  And it is writable just as if they are inviting people to do bizarre horrible things to it.  But...  Ugh.

  • In other retro-nonsense news RetroArch is coming to Steam.  (Ars Technica)

    Of course you can download it for free right now, and it will still be free on - AARGH.


    You have another 24 hours to grab it.

  • A single Atari 2600 cartridge just sold for the price of a four-bedroom house in Bozeman, Montana  (Ars Technica)

    Or...  Wait.  No, it didn't sell.  Faith in humanity restored just a tiny bit.

    You can download the damn thing for free if you really have to.

  • Vaio has a new laptop out.  It seems that the engineers looked at the recently deceased Macbook with its solitary USB-C connector and decided to do the exact opposite.  (The Verge)

  • I haven't read In the Pipeline for a while.  It's a terrific blog that's been going for over fifteen years now, by Derek Lowe, a research chemist working in the pharmaceutical industry.

    The most entertaining section is probably Things I Won't Work With, stories about chemical reagents whose properties are not so much hair-raising as entirely hair-removing.

    A fine example I saw linked on Hacker News is Sand Won't Save You This Time about chlorine trifluoride, a chemical so reactive it will set asbestos on fire.

  • The Epyc 7702P - a single-socket only 64-core server CPU - has snuck out from behind locked doors to post the highest score ever on the SiSoft benchmark.  (SiSoft)

    It posts just shy of 1 TFLOPs double precision, putting it in video card territory.

  • The Radeon VII - which launched at CES in January - has been stamped EXPIRED by AMD.  (VideoCardz)

    It was based on a Radeon Pro card that is still in production (that is, for example, what the new Mac Pro uses).  It was just too expensive to make much sense as a gaming card.

    It will presumably be replaced by a Navi card - at some point.

  • Microsoft has hit one billion installs...  For one single app on one single platform and it's not Windows.  (

    That's not the same as a billion users.  Though they have that too.

  • Dear people who create stuff, stop listening to the people who like your work and pay for it, and pay attention to worthless whining mouth-breathers us journalists instead.  (One Angry Gamer, commenting on a perhaps overly honest piece by VG247)

Anime News

Social Media News

  • How to be Totally Not the Enemy of the People.

  • MSNBC are, as the kids like to say, complete and unmitigated lolcows.

Video of the Day

Well, that was certainly a thing.

But wait there's more.

Music Video of the Day

Bonus Music Video of the Day

No, I couldn't find Dirty Deeds and you can bet that I looked.

Disclaimer: In the future all hardware will be software for 15 minutes.

Posted by: Pixy Misa at 08:04 PM | Comments (2) | Add Comment | Trackbacks (Suck)
Post contains 1795 words, total size 15 kb.

1 TMR OVA3 was pretty good, if not as good as it should have been given the amount of time between OVA2 and it.  OVA4...Left much to be desired - aside from the story being close to slice of life, it felt like it did not have an experienced script writer handling it.

Posted by: cxt217 at Monday, July 15 2019 02:57 PM (LMsTt)

2 Hmmm, but can you build a video capture device that ignores Macrovision encoding? (Surely nobody cares about protecting VHS tapes any more...)

Posted by: Mauser at Tuesday, July 16 2019 12:02 PM (Ix1l6)

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Apple pies are delicious. But never mind apple pies. What colour is a green orange?

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