[LAD] MIDI jitter - was: automation on Linux (modular approach)

[Ralf Mardorf]

Ralf Mardorf wrote:
> David Olofson wrote:
>> On Thursday 25 March 2010, at 13.32.43, David Olofson 
>> <david at olofson.net> wrote:
>>  
>>> On Thursday 25 March 2010, at 12.49.31, Ralf Mardorf 
>>> <ralf.mardorf at alice-
>>> dsl.net> wrote:
>>> [...]
>>>
>>>    
>>>> Btw. the
>>>> graphics has access to the main memory, unfortunately it's a shared 
>>>> RAM,
>>>> OTOH I used HPET so unwanted interrupts because of a shared RAM
>>>> shouldn't be the cause, if I do understand the workings of HR timers
>>>> correctly.
>>>>       
>> [...interrupts, DMA etc...]
>>
>> BTW, the most common problem with graphics and realtime systems seems 
>> to be drivers abusing PCI port blocking as a performance hack. When 
>> the command buffer on the video card is full, the PCI bus blocks the 
>> CPU (completely - no IRQs, no nothing), instead of the driver going 
>> to sleep and waiting for an IRQ or some other proper solution. Might 
>> improve the 3D framerates slightly, but kills lowlatency audio...
>>   
>
> Mobo: M2A-VM HDMI
> Graphics: ATI Radeon X1250-based graphics, *onboard*
> Slot for another graphics is an PCI Express slot, no AGP etc.
>
> The HDMI card is demounted from the PCI Express slot and HDMI is 
> disabled by the BIOS.
> I'm not using a proprietary 3D driver and I wasn't able to test one, 
> because it doesn't work using Linux, even though there is a 3D driver 
> for this card and Linux, perhaps the problem is "...-based".
>
> The USB MIDI interface is a 1 in and 1 out, very cheap swissonic.
>
> I suspect the graphics and the USB device causing to much MIDI jitter.
>
> I need to search for an old test, but have no time to do it right now, 
> but I do remember that Windows without HPET was better, than Linux 
> with HPET as sequencer timer source, while all other Linux sequencer 
> timer sources were much more out of time.
>
> Btw. I don't think that Windows would solve this issue for me, the 
> jitter for my current system is bad with both OSs. I know people where 
> Linux is bad and Windows does solve this issue ... perhaps Windows 
> will cause other issues for them ;).

My PCI Envey24 based card at least gives access to one of the Envy's 
MPUs, unfortunately I wasn't able to use the Terratec EWX 24/96 MPU. I 
tried different circuits using a BreadBoard. I won't buy a MIDI cable 
from Terratec ;).