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Frustrating xQueueCreate() limitation

Posted by Travis Griggs on January 22, 2013
I'm trying to use a queue to buffer characters from my uart ISR to a background task. I want the queue to be 512 bytes long. This is unfortunately impossible, because the type of the size argument is `unsigned portBASE_TYPE` which for the xmega256a3 is a single byte (`char`). Is there a reason the maximum size of a queue floats with `portBASE_TYPE`? Rather than uint16_t?

I'm curious if others have hit the same limitation, and what, if anything, they've done about it.

RE: Frustrating xQueueCreate() limitation

Posted by Richard on January 22, 2013
This is only the case on 8-bit architectures. It has been mentioned a few times (you can search the support archive on the FreeRTOS site), but not for years as most new projects are using 32-bit architectures. The simple thing to do is change the definition of portBASE_TYPE in portmacro.h, but it will make your code larger and less efficient.

As an aside, many of the FreeRTOS demos use queues to pass characters into and out of interrupts to provide a simple example of tasks and interrupts communicating, but unless the throughput is very low (a command console for example), it is not the recommended way of writing production code. Using circular buffers, preferably with a DMA, is much more efficient.


RE: Frustrating xQueueCreate() limitation

Posted by Travis Griggs on January 23, 2013

RE: Frustrating xQueueCreate() limitation

Posted by GregK on January 23, 2013

travisgriggs: might you past definition of uxCriticalNesting in your port:
for example: unsigned portBASE_TYPE uxCriticalNesting = 0xFFFF;

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