[ardour-dev] Ancient history? - Problem identified

[David Gatwood]

On Nov 11, 2004, at 12:40 PM, Jan Depner wrote:

> On Thu, 2004-11-11 at 11:56, Mark Knecht wrote:
>
>>    So, my first, somewhat obvious thought, is that drawing pink boxes
>> is a process of moving a number of pixels to the screen. I presume you
>> are using a more modern AGP based archtecture? If you are running an
>> older PCI graphics adapter then you're moving those pixels across the
>> same bus that your audio is moving across to go to and from the disk
>> which would probably cause some problems.
>>
> 	Even using AGP you're running over the PCI bus.

Well, more accurately, AGP is running over -a- PCI bus.  Not the same 
one as your sound card or SCSI card, though.

AGP has to be on its own PCI-based bus because the clock rate is 
different than stock PCI....  Well, AGP 1x is 66 Mhz, so I guess in 
theory you could run AGP 1x over a slightly modified 66 MHz PCI bus, 
but AGP hardware can't necessarily fall back to 33 MHz speeds, so it 
would be a train wreck if you designed the hardware to share a single 
bus with most PCI devices....

However, you're right that AGP is basically just PCI at a potentially 
different clock speed multiplier with some extra bus bursting stuff 
hacked on top.  Kind of cool, as it means that you can write a single 
driver for AGP that works correctly for PCI devices as long as you 
don't check the error return from enabling the AGP-specific bus modes.  
:-D

But I digress.


David