[Rtai] SCSI/IDE or other solutions?

[Paolo Mantegazza]

Hossein Aminaiee wrote:
> Hi,
> 
> I need to log some data to a file from RTAI/LXRT task with a data baud 
> rate of about 10MB/s. And I have two solutions in mind:
> 1. Opening a file and simply logging the data to the IDE hard disk.
> 2. Installing a SCSI hard disk and using possibly available API for the 
> SCSI interface.
> 
> I wonder if anyone knows whether RTAI has API for the SCSI interface so 
> the task won't switch to the Linux/NONrealtime mode?
> Is there any other solutions?
> 
> Appreciate any helps in advance.
> 

The solution is to use a buddy Linux task/thread, enabled for RTAI but 
not made hard real time, that receives data from the hard real time LXRT 
task using RTAI IPCs, speediest is shared memory, maybe with with non 
blocking SCB support, and then write to disk using standard Linux. See 
CVS "showroom/v3.x/user/scb".

You might want to give a try to the available native RTAI support for 
sync/async Linux servers, see an example in CVS 
"showroom/v3.x/user/linux_server".

My experience, an old one though, back to RTAI birth in 1999, showed 
that with such a scheme logging 5 MB/s to disc was possible but not 
easy. A large buffering was required to avoid loosing data and as a raw 
as possible use of disk access functions required. There has been some 
progress though.

Paolo.



> Regards,
> Hossein
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