Re: [linux-audio-dev] mpu401 fifo scheduling on linux2.4.18

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Subject: Re: [linux-audio-dev] mpu401 fifo scheduling on linux2.4.18
From: Frank van de Pol (fvdpol_AT_home.nl)
Date: Fri Nov 22 2002 - 01:33:02 EET


Hi Bruce,

the cmpci cards have the same hardware design error as the older soundblaster
cards (eg. SB16/AWE64). The cards lack the ability to generate interrupts on
transmit fio empty, and have only one byte of fifo (hmmm.. that should be
named register instead of fifo :-).

If you want to drive your external MIDI gear, just use an interface which
has a decent MIDI port. In case you do not have the option to fix the
hardware, you can work around the defect using a polling driver or (in case
of ALSA) use a high (2 kHz) timer frequency instead of the standard 100 Hz.

Frank.
 

On Thu, Nov 21, 2002 at 09:42:09PM +0000, Bruce M Beach wrote:
>
> Hello All
>
> I'm sending some midi data to synthesizer for playback
> and it appears that the fifo /dev/midi (cmpci mpu401 driver)
> is not emptying as fast as it should(could), since the play back
> is highly irregular. Here are some numbers.
>
> 1) The timeing slice remains constant at 30 msec +/- 3usec,
> timed both at the beginning and end of the loop,
> so the irregularities are not due to loop variations.
>
> 2) A maximum of 64 bytes burst, with around 5 bytes normal
> and an average of 1 byte (say) (ie many slices do nothing)
> can occur during a slice, the buffer for the driver is
> 128 bytes with around a maximum capability of around 116 bytes
> transmitted per slice, so the midi channel can easily sustain
> the transmission rate at the rate I am sending information.
>
> 4) System load while the program is running is around 0.1%
>
> 5) The midi performance remains the same even if I do something
> like build the kernel, and untar some package say glibc at
> the same time.
>
> When I say irregular I mean, for instance on a run of 16th notes
> the notes will radically speed up and slow down. The notes all
> have the correct pitches and voice changes etc. are all happening
> correctly. Just this strange tempo problem.
>
> Any thoughts or suggestions would be welcome.
>
> Bruce

-- 
+---- --- -- -  -   -    - 
| Frank van de Pol                  -o)    A-L-S-A
| FvdPol_AT_home.nl                    /\\  Sounds good!
| http://www.alsa-project.org      _\_v
| Linux - Why use Windows if we have doors available?


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