[ColorForth] 25x graphics

[Mark Sandford <pagercam@xxxxxxxxx>]

The problem as it always seems to be is bandwidth.

1024*768*72Hz = 56.6 MWords (assuming 18bit video)
if this amount has to be read into and then pushed out
this requires a net bandwidth of 112 MWords/Sec and the 
SRAM spec'ed is only clocked at 200MHz with a two cycle
latency so don't expect to get all the bandwidth anyway.
A special video out port would help but, with 25 processors
bandwidth was always going to be limited, especially with 
the small per processor local memories.  If you only
want NTSC/PAL video then there isn't much of a problem
but you really need dedicated video resources for the
higher resolutions/bandwidths.

--- Mark Slicker <maslicke@xxxxxxxxxxx> wrote:
> I was thinking a bit about how one might implement video using the
> 25x. The 25x apears powerful enough to eliminate the need for a
> frame buffer. Some quick calulations will show that a core at 2400
> MIPS is
> capable of updating a screen of 1024x768 pixels at 60 Hz. 18 bits are
> capable of a respectable number of colors. The parallel architechture
> should allow for many interesting stratagies for drawing. 
> 
> Perhaps someone could tell me this, I don't know much of electronics
> yet,
> how would the electrical interface for the video work? I've
> implemented a
> VGA video controller once on an FPGA, it was very simple. The
> vertical and
> horizontal syncs were generated by counters and additional logic. The
> colors (RGB) were either on or off for an 8 color display. Every
> thing 
> was calculated based off a fixed clock. With this interface, I'd
> assume
> you'd need some digital to analog converters, and perhaps something
> to
> syncronize everything to get the timing right. Let me know what you
> know
> about this, or perhaps point me in the right direction (books, links,
> 
> ect).
> 
> Mark
> 
> 
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