Saturday, September 19

Geek

Daily News Stuff 19 September 2020

Pieces Of Ten Edition

Tech News

  • Now if you want to take some pictures of the fascinating witches who put the scintillating stitches in the britches of the boys who put the powder on the noses of the faces of the ladies of the court of King Caractacus you're too late!  (TechReport)

    Because they've just sold out.

    They being the RTX3080 and both models of the PlayStation 5.


  • The WeChat and TikTok bans kick in on Sunday.  (Tom's Hardware)

    Good.


  • VueJS has hit 3.0.0.  (GitHub)

    I haven't done anything real in it, but it does seem to be the least sucky of the major JavaScript frameworks.


  • Based solely on watching videos of Dragon Spirit I have retroactively determined that the Imagine included a cartridge slot.  It could take ROM cartridges mapping up to 128k of address space (plus optional bank switching) or a RAM cartridge for an additional 128k of system RAM.

    The system assigns a single 10-bit bank register to the cartridge port, and leaves it up to the cartridge hardware to determine how to deal with it, but in theory it could support 1024 128k banks for a total of 128M of ROM (or indeed RAM).


  • That means that the big feature of the Imagine 1100 wasn't expandable RAM, but that it came with 128k of system RAM and 256k of video RAM.  You could use the same 128k RAM cartridge to bring system RAM up to 256k, but video RAM wasn't expandable.

    The 1000 and 1100 used page mode RAM, while the 1200 used faster nibble mode RAM, so RAM expansion cartridges weren't perfectly compatible.  They did work, but ran slower than system-specific models.


  • In other fantasy computer news I needed exactly one and a half bits to add a whole new exciting family of addressing modes to the Imagine and clean up an untidy corner of the instruction set.

    I found them.

    Now PC relative addressing only has a range of -128 to +127* instead of -512 to +511, but every instruction has access to special hardware registers, alternate register banks, and on-chip RAM, if they exist in this particular implementation of the CPU.

    So, for example, the DSP variants define AL and AR as left and right audio accumulators, and multiple banks for ABCD and WXYZ, but there was no standard encoding for accessing those registers outside of the specific MAC and BANK instructions.  The OUT $01E, AR to output a calculated sample to the right audio DAC had to be custom crafted into the DSP.

    This new method also encodes 10-to-20-bit conversions like LD A, WL which previously was only possible via LD AB, W - and even that was a special instruction distinct from standard LD.

    These methods require a two-byte instruction encoding, but the second byte is similar to the format used for indexed addressing, rather than a big nasty ad hoc mess.

    This is also how supervisor mode (on variants with a supervisor mode) access the segment and address extension registers (on variants with segment and address extension registers), and how multi-threaded versions spin up and synchronise threads.  None of that will be present in the initial version, but it's all defined so I won't trip over it later.

    * Unless you use indexed mode with P + immediate offset, which has a full 10-bit or 20-bit range but uses one or two extra bytes.


Retro Gameplay Video of the Day



Quick precis: MSX1 bad.  MSX2 pretty good actually.  Also, most MSX systems apparently had two cartridge slots.  Hmm.



Bonus Retro Gameplay Video of the Day



This is Dragon Spirit captured from original arcade hardware.  The video isn't as sharp as from an emulator, but it's the real deal.

Listening to the sound, I'm pretty sure it's using three music voices plus two voices for sound effects.  There are a number of places where you'd expect a fourth instrument to come in, and it never does.

The Imagine can reasonably do five voice wavetable synth at 3MHz, and I've assigned eight sets of registers to the DSP so the other three sets can be used for sound effects, which require less complicated processing.  (The hypothetical Imagine 1200 from 1987 doubles everything, so 10 wavetable voices and 16 sets of audio registers.)

I really like the first couple of tracks here.  Super catchy.


Extra Bonus Retro Gameplay Videos of the Day

Last ones, I swear.

The first is Dragon Spirit on an MSX2 system - 3.5MHz Z80A, 256k of system RAM (though I believe it ran in 64k), and 128k of video RAM.

The second is Dragon Spirit on a Sharp X68000 - 10MHz 68000, 1M system RAM, 512k bitmap video RAM, 512k tile video RAM, and 32k sprite RAM.




The X68000 version definitely looks better, but the MSX system isn't bad at all.  I believe this was a disk-based game and not a cartridge, so that's actually running from just 64k of RAM.  There are some odd hitches in the music on the MSX that aren't present on the X68000, possibly because it had an 8 voice sound chip rather than just 3.


Disclaimer: Bleep bloop.

Posted by: Pixy Misa at 06:13 PM | Comments (4) | Add Comment | Trackbacks (Suck)
Post contains 861 words, total size 7 kb.

1 I mean, I really don't like chinese spyware, but I also really don't like the gummint banning it.  Like, I really hate disney, and I would love too see the whole place burned (in Minecraft) and the executives haning from lampposts (in Minecraft), but I wouldn't be in favour of the gummint banning them.  Maybe prosecuting them for kiddie fiddlin', and forcing the survivors to register as foreign agents, but not banning them.

Posted by: normal at Sunday, September 20 2020 02:32 AM (obo9H)

2 Also, once I comment using firefox, I can't scroll above my own comment.

Posted by: normal at Sunday, September 20 2020 02:33 AM (obo9H)

3 FWIW, using Firefox 80 on Windows 10, I don't have the behavior normal reported in the previous post.  After I post this I'll see if I have the scrolling issue.

Posted by: Rick C at Sunday, September 20 2020 08:06 AM (eqaFC)

4 No repro on the scrolling.

Posted by: Rick C at Sunday, September 20 2020 08:06 AM (eqaFC)

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




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