Stefan Viljoen <pov### [at] polardcom> wrote:
> From http://www.worldofspectrum.org/faq/reference/sereference.htm:

> ---
> Memory is paged in 8K banks from either the DOCK or the EX bank

  This talks about the RAM, not the reason why the pixels are arranged as
they are.

-- 
                                                          - Warp

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Warp wrote:

> Stefan Viljoen <pov### [at] polardcom> wrote:
>> Which ZX Spectrum video mode was this?
> 
>   The ZX Spectrum has exactly one video mode.
> 
>> 'pedia says there are / were lots and lots of them - what mode does this
>> arrangement refer to? The lowest res one?
> 
>   I don't know which article you are reading, but it's definitely not
>   about
> the ZX Spectrum.
>
 
http://en.wikipedia.org/wiki/ZX_Spectrum_graphic_modes

?
-- 
Stefan Viljoen

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Warp wrote:

> Stefan Viljoen <pov### [at] polardcom> wrote:
>> From http://www.worldofspectrum.org/faq/reference/sereference.htm:
> 
>> ---
>> Memory is paged in 8K banks from either the DOCK or the EX bank
> 
>   This talks about the RAM, not the reason why the pixels are arranged as
> they are.

Hmm. Wouldn't it make sense? The video display is just visible RAM by 
definition... isn't it? Or am I mistaken?

I. e. if you can only address an 8K page at a time, and access to memory is 
limited by the last-triggered interrupt, and the limitations / maximum word 
size of your architecture.

I. e. on one tick you can address even lines.

On the other you can address odd lines.

Given that 8K paging is your "chunk limit", wouldn't that explain why the 
video pixels are arranged in such a way as you describe? 

Everything fits if you assume you can only address 8192 bytes at a time 
during any given interrupt - you CANNOT address the whole screen, because 
your word size is too small.

Contrast with an IBM PC with a VGA card. You can comfortably get a linear 
address into the entire 320x200 screen (64000 bytes) with any of the CPU's 
16 bit address registers. With an 8 bit address register you can't? 

So you arrange your video RAM (which you can't all address at once with an 8 
bit address register) to "give" you alternating blocks on an interrupt which 
is acted upon by your memory controller, effective switching contexts with 
each tick?
-- 
Stefan Viljoen

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Stefan Viljoen <pov### [at] polardcom> wrote:
> http://en.wikipedia.org/wiki/ZX_Spectrum_graphic_modes

  The "ZX Spectrum clones" are not ZX Spectrum. The standard ZX Spectrum had
only single video mode.

-- 
                                                          - Warp

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Invisible wrote:
> Dude, I thought this was just an urban legend! O_O

Nope. When your clock speed is in the kilohertz range, it's pretty easy.

-- 
   Darren New, San Diego CA, USA (PST)
     Is God willing to prevent phrogams, but not able?
       Then he is not omnipotent.
     Is he able, but not willing, to prevent phrogams?
       Then he is malevolent.

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>> Dude, I thought this was just an urban legend! O_O
> 
> Nope. When your clock speed is in the kilohertz range, it's pretty easy.

Perhaps you mean "when your clock speed is in the kilohertz range and 
all opcodes take a deterministic number of clock cycles to fetch and 
execute"?

Even then, it seems highly unlikely to me that anybody would actually 
work out which opcodes yield which EM intensity and somehow produce a 
carrier wave of the exact right frequency and precisely modulate its 
intensity... This would surely be a vast engineering task.

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> Perhaps you mean "when your clock speed is in the kilohertz range and all 
> opcodes take a deterministic number of clock cycles to fetch and execute"?
>
> Even then, it seems highly unlikely to me that anybody would actually work 
> out which opcodes yield which EM intensity and somehow produce a carrier 
> wave of the exact right frequency and precisely modulate its intensity... 
> This would surely be a vast engineering task.

With the ARM processor it would be easy, as all the "standard" instructions 
take the same time and all are 32 bits.  You can easily look up how each 
part of each instruction maps to each of the 32 bits and then decide what 
patterns to send.  You could even probably keep 4 or 6 bits the same (eg to 
do an ADD instruction) and then just set the rest to whatever you want to 
make your pattern (it would just mean random registers got added and stored 
in other ones etc).

I would imagine after a bit of trial and error of different 00000111111 and 
000111 type patterns you could get it working.

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scott wrote:


>> intensity... This would surely be a vast engineering task.
> 
> With the ARM processor it would be easy, as all the "standard"
> instructions
> take the same time and all are 32 bits.  You can easily look up how each
> part of each instruction maps to each of the 32 bits and then decide what
> patterns to send.  You could even probably keep 4 or 6 bits the same (eg
> to do an ADD instruction) and then just set the rest to whatever you want
> to make your pattern (it would just mean random registers got added and
> stored in other ones etc).
> 
> I would imagine after a bit of trial and error of different 00000111111
> and 000111 type patterns you could get it working.

Granted, doing something like that would be technically brilliant in my 
book.

But to what end?

There are ways to waste time and then there are WAYS to waste time...! ;)

The only people you might impress with something like that would be your D & 
D buddy whose got skin like a mole and never leaves his basement and his PC 
except to DM your newest AD & D session or chair the local Warhammer club's 
meeting.

Most other people would probably just go "dude WTF!"
-- 
Stefan Viljoen

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Stefan Viljoen wrote:

> Granted, doing something like that would be technically brilliant in my 
> book.
> 
> But to what end?
> 
> There are ways to waste time and then there are WAYS to waste time...! ;)
> 
> The only people you might impress with something like that would be your D & 
> D buddy whose got skin like a mole and never leaves his basement and his PC 
> except to DM your newest AD & D session or chair the local Warhammer club's 
> meeting.
> 
> Most other people would probably just go "dude WTF!"

...I write computer programs in a non-strict purely-functional 
programming language with extended Miller-Hindley type inference, 
monadic effects and nested data parallelism.

I win?

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> Most other people would probably just go "dude WTF!"

Not if you got to play "never gonna give you up", made a video of it and 
uploaded it to youtube :-)

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