From: Florian G. Pflug (
Date: Mon May 08 2000 - 19:38:17 EDT

On Thu, May 04, 2000 at 02:08:50AM -0500, Peter E. Thomas wrote:
> Hello All-
> I have a question about how the ucsimm will handle a realtime task. My
> setup is basically this:
> 1. PC running Windows NT, with an ethernet card
> 2. ucsimm connected to PC via ethernet
> 3. a "decoder" card connected to the SPI port on ucsimm.
> What I want to do is send a packet to the ucsimm containing coded speech.
> The data from this packet will be taken out and sent out the SPI port.
> Now, it needs to be sent out the SPI port in a special fashion. Every 125
> micro seconds, I need to send 2 bytes. I figure that when I send the TCP
> packet to the ucsimm, I will give it about 1000 bytes to work with.
> The same thing needs to work in reverse. The decoder card will be sending
> 2 bytes 8000 times a second through the SPI to the ucsimm. I need the
> ucsimm to buffer some ammount (I don't know how much...) and then send the
> packet to the Windows NT box.
> It seems this is going to be VERY tight, maybe not possible. How long
> should I bufffer data in the ucsimm when it is reciveing from the decoder?
> How long does it take to send a 1000 bytes packet? a 100 byte packet?

We did _exactly_ the same thing (what chip to you want to hook the uCsimm
too?) - But our data rate was slower, we only needed 4kBytes/Second. This
make an interrupt frequency of 2kHz. We are using the
realtime-uClinux-patches from kwonsk ( - somewhere in
contribute i think), and the module handles this load without problems -
even nfs keeps working.

Without the realtime patches you loose data every time the simm does network
or serial transfer.
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