Thread View: comp.sys.acorn.tech
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Started by James McCoull
Fri, 08 Jan 1993 05:16
VIDC Programming Question
Author: James McCoull
Date: Fri, 08 Jan 1993 05:16
Date: Fri, 08 Jan 1993 05:16
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Just posting to ask for help on some low level VIDC programming. I'm trying to program the VIDC to generate vsync interrupts after each scan line - for both screen splitting, palette changing and a few other odds and ends. Unfortunately timers are no good for my task, I *must* have real vsyncs. So far I'm having a little trouble due to lack of documentation (anyone know where I can find some documentation on the VIDC chip? so far all my knowledge has come from looking at the OS and playing around finding what the registers do). Basically I have come up with two methods, but both do not work. The first is the simplest: (1) I gather that a vsync occurs when the vertical position passes the value in the VDE (vertical display end) register. So I had thought by setting the VDE to VDS+1 (vertical display start), I would receive a vsync after the first line of the display - then on this interrupt i could increase the value in VDE by 1,... and so forth. However while all these registers do seem to take effect immediately (unlike the vinit,vstart,vend buffer registers - which seem to be latched on vsync) - this method doesnt seem to work. It appears that the new VDE value is ignored (something to do with the "should i be displaying new data" logic on the VIDC chip?). I've tried a less ambitious example of only a single midscreen interrupt but with no success. (2) My other 'method' is more complex it involves reprogramming the VC (vertical cycle), VSW (vertical sync width) to produce the same effect. However while i've only managed to get this method to work in a minimal sense. I've managed to get a mid screen split using this method, but the video display cuts out for at least one scan line... and i get about 8 distorted lines (due to syncing trouble?). Would any experienced VIDC programmer care to help me? - or anyone care to post any VIDC documentation? I'm at the hear tearing stage!!! Preferably all followups to the news (as i don't have access to a proper unix account)
Re: VIDC Programming Question
Author: Michael Hardy
Date: Fri, 08 Jan 1993 10:03
Date: Fri, 08 Jan 1993 10:03
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In article <1993Jan8.051650.17939@newsroom.utas.edu.au> u894776@postoffice.utas.edu.au (James McCoull) writes: >Just posting to ask for help on some low level VIDC programming. > >I'm trying to program the VIDC to generate vsync interrupts after each scan >line - for both screen splitting, palette changing and a few other odds and >ends. Unfortunately timers are no good for my task, I *must* have real >vsyncs. So far I'm having a little trouble due to lack of documentation >(anyone know where I can find some documentation on the VIDC chip? You'll find the info you need in: Acorn RISC Machine family Data Manual. VLSI Technology Inc. (1990) Prentice Hall, Englewood Cliffs, NJ, USA: ISBN 0-13-781618-9 If you quote these details to your local friendly bookshop, they should be able to order the manual for you. (There may by now be a newer version that covers more recent chips such as the ARM 600 series, the ARM 250 and the new VIDC. Your local VLSI office could probably advise you on this.) - Michael J Hardy Technical Publications Email: mhardy@acorn.co.uk Acorn Computers Ltd Telephone: +44 223 254352 Cambridge TechnoPark Fax: +44 223 254270 645 Newmarket Road Telex: 817875 ACORN G Cambridge CB5 8PB England Disclaimer: All opinions are my own, not Acorn's
Re: VIDC Programming Question
Author: Simon Burrows
Date: Fri, 08 Jan 1993 21:42
Date: Fri, 08 Jan 1993 21:42
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In article <20957@acorn.co.uk> mhardy@acorn.co.uk (Michael Hardy) writes: > >You'll find the info you need in: > > Acorn RISC Machine family Data Manual. VLSI Technology Inc. (1990) > Prentice Hall, Englewood Cliffs, NJ, USA: ISBN 0-13-781618-9 > >If you quote these details to your local friendly bookshop, they should be >able to order the manual for you. My local branch of Dillons bookshop has a couple of copies. The price marked on them is 26.95 UK pounds. Unfortunately VLSI were recently giving away free copies through Coin-Age Ltd, but there are none of these free copies left. Simon ------------------------------------------------------------------------------ Simon Burrows smb@cs.nott.ac.uk psyhsmb@unicorn.nott.ac.uk +44 533 712030 ------------------------------------------------------------------------------
Re: VIDC Programming Question
Author: Adam David
Date: Sun, 10 Jan 1993 10:24
Date: Sun, 10 Jan 1993 10:24
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In <20957@acorn.co.uk> mhardy@acorn.co.uk (Michael Hardy) writes: > Acorn RISC Machine family Data Manual. VLSI Technology Inc. (1990) > Prentice Hall, Englewood Cliffs, NJ, USA: ISBN 0-13-781618-9 >If you quote these details to your local friendly bookshop, they should be >able to order the manual for you. I tried this last year, after waiting a few weeks I got the answer: "Sorry, it's out of print." Does anyone know whether it has been reprinted, or do we have to rely on the chance of finding an old copy somewhere? -- Adam David (adamd@rhi.hi.is)
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