Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!ucsd!ames!lll-tis!lll-winken!uunet!mcvax!ukc!stc!idec!camcon!anc
From: anc@camcon.co.uk (Adrian Cockcroft)
Newsgroups: comp.arch
Subject: Re: Sw vs. Hw BitBlit (CharBLT)
Summary: 82786 has charblt
Keywords: bitblt
Message-ID: <1848@titan.camcon.co.uk>
Date: 8 Aug 88 08:59:15 GMT
References: <399@ma.diab.se> <76700044@p.cs.uiuc.edu>
Organization: Cambridge Consultants Ltd., Cambridge, UK
Lines: 32

In article <76700044@p.cs.uiuc.edu>, gillies@p.cs.uiuc.edu writes:
> 
> Re: Render characters
> 
> Another approach (taken by the Xerox DLion) is to have a separate
> instruction just for displaying characters.  This instruction, called
> (appropriately) "TextBLT", knows about the font table formats and
> specialized for displaying rectangular blobs of text.  TextBLT is also
> implemented in microcode, on the DLion's AMD2900-based CPU.

The Intel 82786 has a charblt instruction. There are two forms, in the nicest
one you define a font to the chip, up to 256 16x16 pixel characters mapped
through an indirection table so that e.g. all unwanted chars map to the same
glyph, you then give it a string and a charcount and the CHARBLT instruction
draws proportionally spaced characters for you (the font can be kerned for
italic). This runs at full memory bandwidth speeds. The font has a header
for each glyph giving its size and some mode control

The 82786 can also have a very high memory bandwidth of 40 Mb/s on a 16 bit
wide bus. It uses page mode DRAMS in two banks interleaved so that a new word
is read every 50ns. A burst lasting about a microsecond fills the 25 word
FIFO that feeds the video output registers, leaving plenty of memory
bandwidth for drawing operations. I think the blitter also does a block fetch
although it might use a RMW cycle. The CHARBLT runs at 20000 chars/sec.
The CHARBLT can draw 1 bit deep characters into 1,2,4 or 8 bit deep bitmaps.



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