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Re: FreeBSD TCP/IP stack , time to send ?


On Tue, 2005-02-22 at 17:14 +0100, sebastien Couret wrote:
> Hi guyz,
> 
> I would like to know if the time to send a packet on an ethernet network with 
> an ecos device could be bounded.
>   
> Let's imagine we have a perfectly silent ethernet network (no packets are 
> currently transmitted) to avoid CSMA-CD retransmissions.
> We have choosed to use FreeBSD TCP/IP stack port.
> 
> As TCP/IP stack work as two separated threads, i imagine that the scheduler 
> must first pass control to one of those threads which could take a fixed time 
> as ecOS is "realtime".
> 
> Can we garantee a maximal amount of time for sending and UDP datagram with 
> eCOS or not ? 
> 
> If so, Is it realistic to believe it is possible to send it in 10ms ? 1ms ? 
> 0.5 ms ? with a MPC8270 CPU on the embedded device. 

Packets are sent directly by the issuing thread unless the device
is already busy/saturated.  Thus, the "time to send" is as fast
as the processor can get it ready, which should be less than your
smallest number of 0.5ms

The network stack only uses the auxiliary threads for processing
incoming packets, not sending packets.

-- 
------------------------------------------------------------
Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
------------------------------------------------------------


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