Re: Task switching in the case of the bus congestion

On Mon, 04 Feb 2008 10:16:02 -0600, Vladimir Vassilevsky wrote:

Recently I run into the following problem: the CPU gets blocked for a
relatively long period of time (~50us) because the bus is occupied by
the high priority DMA transfer to the slow peripheral device. I solved
that particular problem by changing the bus priorities and breaking the
long DMA transfer into a series of the short bursts. I don't like this
solution because it is too specific to the application and it also
increases the bus overhead.

However even if the bus is blocked, the CPU is still able to respond to
the interrupts and execute the code using cache and internal memories as
long as the bus is not required. So, if the current task is blocked
because it needs to access the bus, it could make sense to switch to the
different task.

But, the BlackFin architecture doesn't have any means to activate the
switching of the contexts in the case of the congestion on the bus.

Do you know of any RTOS and hardware architecture which would allow to
do that?


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant http://www.abvolt.com

Not off the top of my head -- in my experience when the bus is blocked
the processor just stops, and there's not a darn thing that software can
do about it.

The only thing that I can think of to fix this is to anticipate such DMA
transfers, and make sure that you have dual-port memory if they are going
to be an issue.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
.

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