[HN Gopher] Looking at the Atari 400 Part 1 - By Paul Lefebvre
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Looking at the Atari 400 Part 1 - By Paul Lefebvre
Author : rbanffy
Score : 19 points
Date : 2024-03-25 13:08 UTC (1 days ago)
(HTM) web link (www.goto10retro.com)
(TXT) w3m dump (www.goto10retro.com)
| PaulHoule wrote:
| The Atari 400 and 800 are interesting to me because they had a
| different video architecture from most of the other computers of
| its generation. Most systems of the day had a simple frame buffer
| and/or "tile" system where the tiles are defined by a character
| ROM so you could draw an A to the screen by writing a 65 to the
| right memory system. Some systems (like the Apple ][) could work
| in a split screen mode where part of the screen was bitmapped and
| another part was text but this was an exception instead of the
| rule.
|
| The Atari machines on the other hand had two chips that worked
| together to prepare the display data which meant that you could
| choose a different video mode for each line which gave developers
| a lot of flexibility and reduces the display RAM requirements for
| a machine that launched with just 8k of RAM. (For instance if a
| horizontal line was all one color you did not need that frame
| buffer line; if you wanted to do horizontal or vertical scrolling
| that could be configured by setting the offset of where scanning
| starts)
|
| See https://en.wikipedia.org/wiki/Atari_8-bit_family#Design
| chasil wrote:
| I remember the term "player missile graphics" from the day.
| Google has several articles on the subject.
|
| https://www.atariarchives.org/creativeatari/PlayerMissile_Gr...
| ofrzeta wrote:
| Also Display List Interrupts: they made more colors per
| screen and other things possible.
|
| https://www.atariarchives.org/creativeatari/Display_List_Int.
| ..
|
| https://playermissile.com/dli_tutorial/
|
| It's great that today you can get so much information online.
| Back then it was much harder so I could never quite wrap my
| head around that stuff as a teenager.
| glimshe wrote:
| That was pretty interesting from an engineering perspective,
| and highlighted the different compromises computer makers made.
| The Atari could display certain types of graphics, like
| gradients, trivially - while it could struggle with fine
| bitmaps unlike systems that mapped a bitmap buffer straight to
| screen.
|
| These compromises gave each 80s system an unique artistic
| style... Unlike current consoles which are just triangle and
| shader pumping machines with differences largely on throughput.
| PaulHoule wrote:
| Most machines of that era had a pretty standard architecture
| except for a few strange ones like Atari and TI-99/4A
| (minuscule amount of ordinary RAM but a fair amount of "video
| RAM" the CPU can access through ports; no bitmaps, only
| tiles) and the early Sinclair (which used Lancaster's "cheap
| video" https://www.tinaja.com/ebooks/cvcb1.pdf to delete the
| display controller)
|
| One thing that did matter was color choice. My TRS-80 Color
| Computer had a terrible choice of colors that you'd expect
| from a physicist or electrical engineer, the C-64 had a small
| number of hand-picked colors that looked nice. (Somebody
| ought to tell the people who maintain contemporary terminals
| because I usually have to do ":syntax off" to see what I am
| editing with vi and it was annoying as hell to set up a Linux
| computer attached to a TV this weekend because I was sitting
| at an odd angle which made most colors illegible except for
| white.)
|
| Another interesting fact to me is that 1980s era display
| controllers were conceptually simple but had a huge part
| count in terms of gates because of multiple wide data paths.
| Today it is fun to build them with FPGAs but difficult to
| build them out of discrete parts. I saw an ad in Byte circa
| 1979 for a gfx card for S-100 computers that had much better
| specs than the average home computer but was a fairly large
| board packed with chips on both sides.
|
| Thus most of the home computers had an ASIC display
| controller and projects like
|
| https://www.commanderx16.com/
|
| struggle and wind up using an FPGA or microcontroller for the
| display controller as opposed to something authentic.
| Sometimes though I think it might be fun to try building a
| display controller on a few big breadboards.
| 0xcde4c3db wrote:
| > Sometimes though I think it might be fun to try building
| a display controller on a few big breadboards.
|
| I haven't found a full schematic or analysis anywhere, but
| I've been tempted a few times to try replicating some
| incarnation of Alpha Denshi graphics hardware. It's the
| lineage that led to the Neo Geo hardware, and for any given
| generation has some impressive capabilities despite being
| built (AFAIK) entirely out of memories and standard logic
| chips.
|
| I guess it would be more practical to start with some
| really minimal hardware like Minivader or Dottori-kun
| (which, legend has it, were created entirely due to an odd
| regulation requiring arcade cabinets to be sold as
| "complete" units, and expected to be thrown out by the
| buyer), but that's not as fun (and IIRC they have some
| janky sync behavior that might not work on any display I
| own).
| 0xcde4c3db wrote:
| One way to think of it is as an enhanced version of the Atari
| 2600 graphics chip with a sort of primitive "GPU" put in front
| of it to offload the "racing the beam" stuff. Amiga "copper
| lists" later generalized the concept to drive a larger array of
| relatively simple specialized I/O chips (presumably due to Jay
| Miner).
| PaulHoule wrote:
| Yep, it was really clever how it was built in separate
| stages.
| karmakaze wrote:
| I did a lot of 8-bit Atari programming at the time, and the
| display list was the greatest thing ever. I was a bit surprised
| that other computers had global modes rather than being able to
| mix-n-match and create a custom mode. Double-buffering was also
| trivial, by writing to the other memory area then setting that
| address as the display list starting address in the vertical
| blank interrupt handler.
|
| The C64 had better sprites and sound, but the Atari did more
| with less, with the 2600/VCS being an extreme example. In
| particular the SIO[0] (serial I/O) architecture let peripherals
| work without a lot of logic, whereas the C64 drive had a more
| powerful CPU than the C64 itself. Atari SIO with its daisy-
| chaining, device numbers, and command/response structure is
| sometimes referenced as a precursor to the design of USB. Atari
| SIO was even better in that devices could load their drivers
| over SIO when booted so that devices made in the future could
| be supported without OS/ROM changes or manual driver loading.
|
| [0] https://en.wikipedia.org/wiki/Atari_SIO
| TMWNN wrote:
| The Atari 8-bit machines were ahead of their time. Their graphics
| are so good that an architecture first sold in 1979 was still
| market-competitive among other inexpensive home computers in
| 1987, when the XEGS appeared as the last new model in the series.
| About the only thing that one might miss is built-in 80-column
| graphics. The entire line was (more or less) compatible with each
| other from start to finish, too; far better than Commodore, which
| over the same time period sold at least five different 8-bit
| computer lines, all mutually incompatible with rare exceptions.
| SIO is far superior to Commodore's jumble of serial, user, and
| cassette ports, too. (Did I mention that this all appeared in
| 1979?)
|
| Arguably Atari's sophistication was a disadvantage. The need for
| custom ICs, without an in-house fab like Commodore, and a focus
| on quality manufacturing as opposed to Commodore's slipshod
| methods caused the 8-bit line to be far too expensive compared to
| competitors; in 1979 one might as well have bought an Apple II
| and gain a larger library, far more expandability, and the
| amazing Disk II. By 1982 the Commodore 64 brought (slightly)
| superior graphics and sound at a far lower price. The key year is
| 1983, when Jack Tramiel waged war on the entire rest of the
| industry with massive discounts on the VIC-20 and 64 leading up
| to Christmas; the primary opponent was TI (which indeed
| surrendered in November), but Atari was collateral damage.
|
| That need not have been fatal for Atari, but a) product shortages
| of the new 600XL and 800XL models in 1983 because of mishandling
| of Asian production, b) the massive losses that parent Warner
| Bros. suffered from the collapse of the video game market (which
| Commodore's aforementioned price war contributed to), and c)
| consequent sale of Atari to the same Tramiel after he quit
| Commodore, caused developers to shy away from new software
| releases from 1984 onward. Once the software disappeared, so did
| customers.
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