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On 27/10/2015 11:28 AM, clipka wrote:
> Am 27.10.2015 um 09:29 schrieb Orchid Win7 v1:
>> See, for example, this image:
>>
>> https://i.ytimg.com/vi/O6uwfM8F5uU/hqdefault.jpg
>>
>> It seems to load every 8th line, for the top 6 groups, and then load
>> every 8th line for the next 6 groups, and so on... That's a really weird
>> order. I could understand if it was loading all the odd lines and then
>> all the even lines, but it's much more complicated than that.
>
> Actually judging from the image that seems to be 8 groups, not 6.
Yeah, I can't count.
> The Amstrad CPC had a similar frame buffer arrangement, though a little
> simpler.
>
> In the case of the Amstrad CPC, this was easily explained:
>
> The CRT controllers used back in those days were originally designed for
> text-only display, such as in text terminals: In sync with the cathode
> ray, the CRTC would generate an address into a text buffer, plus a
> separate pixel row address; in normal operation, the former would be
> used to fetch a character code from the text framebuffer; the character
> code combined with the pixel row address would then be used as an index
> into a character ROM, to fetch the bit pattern of a single pixel row of
> the character in question. The CRTC would then fetch that bit pattern
> into a shift register, to control the cathode ray brightness for
> (typically) 8 pixels.
>
> Such controller chips were already widely available back then, while
> dedicated graphics CRTCs were not.
>
> To use such a text CRTC for graphics display with a minimum of
> circuitry, a clean framebuffer layout would have required to make the
> image width a power of 2; in that case you could splice the text buffer
> address into a lower and higher portion (being equivalent to a column
> and super-row address, respectively), and insert the pixel row address
> between the two (as the row address) to generate a framebuffer address.
> But with any non-power of 2 image width, this scheme would either
> utterly break down, or require you to sacrifice precious memory.
>
> Therefore, typically the text buffer address would simply be used as the
> lower portion of the framebuffer address, and the pixel row address
> would be used as the higher portion, resulting in the 8-line interleave
> pattern.
>
>
> In the case of the ZX Spectrum, the framebuffer layout is less easily
> explained: First of all, it doesn't seem to use a dedicated CRTC, but
> has this functionality integrated into a custom chip - which sounds like
> an expensive solution to me. But I guess it is safe to assume that the
> custom chip wasn't designed from scratch, but just combined
> miscellaneous 3rd party integrated circuitry on a single chunk of
> silicon, so in a sense it may have had a text CRTC after all.
>
> However, the display width is 256 pixels, so it would have been easy to
> splice the text buffer address as explained above, and thus get a simple
> frame buffer layout.
>
> One potential reason could be that the framebuffer address
> double-featured as a dynamic refresh address for the DRAM cells. Or the
> designer was so preoccupied with this way of doing it that he didn't
> realize it could be done easier. Or he wanted to keep the design
> flexible to support different screen resolutions.
>
> This still doesn't explain the additional grouping of the image into
> bocks of 64 pixel rows. I must confess I have no idea why anyone would
> want to do that, unless it's /some/ artifact of the CRTC used.
That... is some interesting theorising, actually! Makes the most sense
out of anything I've heard.
>> I was shocked an horrified when I realised that RAM doesn't work this
>> way any more.
>
> It does help with bulk memory access though.
Only if your RAM bus is drastically slower than everything else in the
system...
I always wondered why nobody puts, say, 1GB of RAM onto the same die as
the CPU, so bus speed becomes a total non-issue. And then I read the
specs of the Raspberry Pi and thought "OK, NM..."
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On 26/10/2015 11:31 PM, Jim Henderson wrote:
> On Mon, 26 Oct 2015 22:38:03 +0000, Orchid Win7 v1 wrote:
>> I guess the Pi by itself doesn't do a lot; it's great for building crazy
>> robots, if *electronics* is what you're trying to teach. But you need
>> more components to make a usable computer out of it. And then there's so
>> many other bits plugged in, you lose sight of the fact that the little
>> circuit board in the middle is the part that's actually "doing" stuff.
>
> I've got OpenELEC running on one; it makes a reasonable media server.
>
> Nothing else really plugged in, either. HDMI, external hard drive,
> power. Wireless keyboard/mouse combo that I generally don't use.
At that point, doesn't it kinda make it look like *the screen* is all
the smarts? Not the inconspicuous little box in the corner?
>> It wouldn't hold my attention for ten seconds. And that's kinda my
>> point; kids these days have smartphones in their pockets. Why would they
>> bother with this obsolete thing? (Unless you manage to convince them
>> that its arcane-ness makes it "special" rather than just dumb.)
>
> Lower end equipment can help kids and students understand where the
> technology comes from and how it developed over time. Understanding the
> past is useful to seeing ways in which things can be done in the future.
Oh, I *totally* agree with what you're saying. My question is how you
keep the kids from just glancing at it and going "this is lame!" and
going back to playing Angry Birds or something.
>>> You certainly can do system-level programming on the RPi. How do you
>>> think you get a kernel developed to run on it? ;)
>>
>> You're aware that to this day, the OS includes a closed-source binary
>> blob that only people who sign an NDA are allowed to look inside, right?
>> Literally, you cannot operate the GPU without signing an NDA or using
>> closed-source code. And since this is a mobile phone SoC, the GPU
>> controls the CPU, not the other way around...
>
> Yes, but that's true on a lot of PCs that run Linux as well. That
> doesn't mean you can't do system-level programming on it.
Thanks to backwards compatibility, every IBM PC-compatible starts up in
8080 emulation mode, and has a BIOS that lets you do stuff without even
knowing what model of video card you have. Even then, it surely has 100%
VGA register compatibility, so you can program it that way.
On the Pi, until you poke the GPU, the CPU isn't even *turned on*...
> I think there's a lot you can do that's interesting without any video at
> all.
Oh, really?
[That maybe sounded sarcastic. It wasn't meant to.]
Clearly you've got different ideas to me... What kinda thing are you
thinking?
[Genuinely interested here.]
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On 10/27/2015 6:58 PM, Orchid Win7 v1 wrote:
>> I think there's a lot you can do that's interesting without any video at
>> all.
>
> Oh, really?
>
> [That maybe sounded sarcastic. It wasn't meant to.]
>
> Clearly you've got different ideas to me... What kinda thing are you
> thinking?
>
> [Genuinely interested here.]
Break codes, calculate ballistic trajectories, solve engineering
problems. Run the finances for Lyons tea house. Text processing and games.
And this:
https://plus.google.com/photos/+KenShirriff/albums/6116650756716708097/6116650759320217970?pid=6116650759320217970&oid=106338564628446721517
--
Regards
Stephen
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On 10/27/2015 7:50 PM, Stephen wrote:
>
https://plus.google.com/photos/+KenShirriff/albums/6116650756716708097/6116650759320217970?pid=6116650759320217970&oid=106338564628446721517
>
>
Source:
http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.htmlhttp://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html
--
Regards
Stephen
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On 10/27/2015 7:52 PM, Stephen wrote:
> Source:
>
http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.htmlhttp://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html
>
>
Bugrit!
http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html
--
Regards
Stephen
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On 27/10/2015 07:53 PM, Stephen wrote:
> http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html
Qui-binary...?
My mind is blown.
As an aside, Hackaday.io seems to be full of people building computers
"from scratch", using only individual logic gates. One guy claimed to be
building a computer from nothing but 7400s...
...until you realise that he means the members of the 7400 family that
implement entire counters, encoders, decoders, latches, etc.
Another guy claimed to by building a computer from discrete
transistors... until you realise that he's using an Arduino to control
it. Wuh??
It's interesting to me that the IBM 1401 appears to be a *real* computer
made only from discrete transistors. I'd always assumed that such a
thing would fill an entire warehouse. But it doesn't actually look all
that big...
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On 27/10/2015 07:50 PM, Stephen wrote:
> On 10/27/2015 6:58 PM, Orchid Win7 v1 wrote:
>>> I think there's a lot you can do that's interesting without any video at
>>> all.
>>
>> Oh, really?
>>
>> [That maybe sounded sarcastic. It wasn't meant to.]
>>
>> Clearly you've got different ideas to me... What kinda thing are you
>> thinking?
>>
>> [Genuinely interested here.]
>
> Break codes, calculate ballistic trajectories, solve engineering
> problems. Run the finances for Lyons tea house.
Not sure too many children would be interested in any of those.
> Text processing and games.
Interesting without display capabilities. ;-)
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On 27/10/2015 07:53 PM, Stephen wrote:
> http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html
Only just finished reading this.
Man, that is some special brand of craziness, right there. Mental stuff.
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On Tue, 27 Oct 2015 18:58:19 +0000, Orchid Win7 v1 wrote:
>> Nothing else really plugged in, either. HDMI, external hard drive,
>> power. Wireless keyboard/mouse combo that I generally don't use.
>
> At that point, doesn't it kinda make it look like *the screen* is all
> the smarts? Not the inconspicuous little box in the corner?
Not really, but then again, I connect the HDMI to a receiver that then
sends the output to a projector. So my "screen" is a 10' diagonal image
projected on a white wall.
But it doesn't really matter.
> Oh, I *totally* agree with what you're saying. My question is how you
> keep the kids from just glancing at it and going "this is lame!" and
> going back to playing Angry Birds or something.
By making it interesting, which is done by making it relevant. A lot of
kids are curious about stuff like that.
>> Yes, but that's true on a lot of PCs that run Linux as well. That
>> doesn't mean you can't do system-level programming on it.
>
> Thanks to backwards compatibility, every IBM PC-compatible starts up in
> 8080 emulation mode, and has a BIOS that lets you do stuff without even
> knowing what model of video card you have. Even then, it surely has 100%
> VGA register compatibility, so you can program it that way.
>
> On the Pi, until you poke the GPU, the CPU isn't even *turned on*...
Mine turns on when I plug it in, before the OS is done. That's firmware-
level stuff, generally not the sort of thing I think of with "system-
level" programming.
>> I think there's a lot you can do that's interesting without any video
>> at all.
>
> Oh, really?
>
> [That maybe sounded sarcastic. It wasn't meant to.]
>
> Clearly you've got different ideas to me... What kinda thing are you
> thinking?
>
> [Genuinely interested here.]
Web hosting is the most obvious example. Music streaming, controlling
home automation - lots of IoT-related things, actually.
Jim
--
"I learned long ago, never to wrestle with a pig. You get dirty, and
besides, the pig likes it." - George Bernard Shaw
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On 10/27/2015 8:31 PM, Orchid Win7 v1 wrote:
> On 27/10/2015 07:53 PM, Stephen wrote:
>> http://www.righto.com/2015/03/12-minute-mandelbrot-fractals-on-50.html
>
> Qui-binary...?
>
> My mind is blown.
>
I know and I thought BCD was strange.
>
> As an aside, Hackaday.io seems to be full of people building computers
> "from scratch", using only individual logic gates. One guy claimed to be
> building a computer from nothing but 7400s...
>
> ....until you realise that he means the members of the 7400 family that
> implement entire counters, encoders, decoders, latches, etc.
>
I hope he has a big power supply and lots of fans.
In the mid 70's I built a digital clock out of TTL. It needed 25 amps at
5 volts to drive the logic. A couple of years later I built one out of
CMOS and that would run for an hour on a PP3 battery. (It was mains
powered the battery was for backup.)
> Another guy claimed to by building a computer from discrete
> transistors... until you realise that he's using an Arduino to control
> it. Wuh??
>
The first machine I worked on was the Honeywell H516. It used discrete
components not ICs.
> It's interesting to me that the IBM 1401 appears to be a *real* computer
> made only from discrete transistors. I'd always assumed that such a
> thing would fill an entire warehouse. But it doesn't actually look all
> that big...
That is a media exaggeration. They were forever showing images of
computer systems in enormous clean rooms with technicians in white coats.
One company I worked for had an old PDP 8. It fitted inside a 19 inch
cabinet. I only once opened the door to look at the guts. I then prayed
it would never break. ;-)
> Only just finished reading this.
>
> Man, that is some special brand of craziness, right there. Mental stuff.
Funnily enough. His project reminded me of you. Did you not once write
programs in PostScript or Printer Command Language?
--
Regards
Stephen
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