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. -- | Adrian Cockcroft ..!uunet!mcvax!ukc!camcon!anc -[T]- Cambridge Consultants Ltd, anc@uk.co.camcon or anc@camcon.uucp | Science Park, Cambridge CB4 4DW, England, UK (0223) 358855 (You are in a maze of twisty little C004's, all alike...)