From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <13426df10805281207g51a0f04at5cc48fe8ea7348bd@mail.gmail.com> Date: Wed, 28 May 2008 12:07:24 -0700 From: "ron minnich" To: "Digby Tarvin" , "Fans of the OS Plan 9 from Bell Labs" <9fans@9fans.net> In-Reply-To: <20080528183439.GA8756@skaro.cthulhu.dircon.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <13426df10805271502s7e78ba0dw826dd2f6d982304c@mail.gmail.com> <20080528000641.GA2649@skaro.cthulhu.dircon.co.uk> <775b8d190805280031x17e2f483s1f82640bacd4851f@mail.gmail.com> <20080528183439.GA8756@skaro.cthulhu.dircon.co.uk> Subject: Re: [9fans] OT: supporting multiple VGA cards (was "A shot in the dark") Topicbox-Message-UUID: ae09da6e-ead3-11e9-9d60-3106f5b1d025 On Wed, May 28, 2008 at 11:34 AM, Digby Tarvin wrote: > > I am interested in connecting more than one graphics adapter so that > one can be dedicated to low level diagnostics (rather than the more > usual dual head user interface).. but I am not sure how the hardware > deals with that given that the VGA standard seems to imply that all > the cards would be using identical memory addresses and IO ports. There are Rules such that only one terminal gets to own the "legacy" ports. > Otherwise I would expect PCI to be able to automatically > map resources to non-conflicting addresses/IO ports. They do. It's just the legacy stuff that gets weird. > > In any case my BIOS has a setting which allows selection between AGP and > PCI as 'primary' Video, suggesting that it is indeed possible to have at > least one of each. it is. > > The only thing I can think of is that perhaps the VGA/CGA/EGA etc modes > are suppressed in the non-primary card, leaving only the more advanced > and less standard mode available. But this would be less ideal, as text > mode would be more useful for low overhead diagnostics. if you can convince the OS to use the non-legacy addresses, you could configure BIOS to put your desired debug terminal at legacy addresses and use it for debug. ron