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FreeRTOS: Memory Management

Posted by paulromero on May 22, 2016

Dear Forum:

Is is possible to configure FreeRTOS such that the heap. implementation of prvPortMalloc() etc. can be used on separate heap and ram segments the concurrently ?

More clearly, I would like to use the same memory management algrorithm for two completey separate areas of memory. One is a large ram segment and the other is the default heap segment.

I am almost certan the names of the allocation and free routines must have distinct names and something needs to be done to point the at the right segment during initialization.

Best Regards,

Paul R.

FreeRTOS: Memory Management

Posted by richard_damon on May 22, 2016

You probably want to make a copy of the heap#.c file and give the functions a new name to make the version to handle the separate area. You can then add whatever is needed to force the heap array into the right memory, this is very system dependent.

FreeRTOS: Memory Management

Posted by heinbali01 on May 23, 2016

Do you want two different malloc routines, e.g.:

~~~~ /* Malloc internal RAM. */ void *pvPortMalloc(); void vPortFree();

/* Malloc external RAM. */
void *pvPortMalloc_2();
void vPortFree_2();


Or do you want a single malloc/free couple that manages both areas of memory? In the last case you can use heap_5.c

FreeRTOS: Memory Management

Posted by rtel on May 23, 2016

Further to Hein's post, here is a link with a little more information on heap5: http://www.freertos.org/a00111.html#heap5


FreeRTOS: Memory Management

Posted by paulromero on May 25, 2016

Hi Richard:

I would like to use two different malloc() routines with independent memory management.

I designed a best fit memory management algorithm which has been extensively tested and and moderately analyzed. It is pretty much system independent. All you need to do is point at the chunk of memory you want to use. However, it is not reentrant and the code could use some refinement.

The code that implements the algorithm and the proof of it are attached to this note for your perusal. Can you think of a way to make it safe for use in a multitasking environment without using mutexes ? I assume no one is dumb enough to try to use in an interrupt handler or critical section.

Best Regards,

Paul R.


README.mm_algo (6192 bytes)
basic.h (335 bytes)
memory.h (1893 bytes)
vram_alloc.c (20068 bytes)

FreeRTOS: Memory Management

Posted by richard_damon on May 25, 2016

The simplest way to get mutual exclusion is a mutex, that is the basic purpose of them (which is what gives them their name). The alternative would be to do something to disable task switching for the duration, either with a critical section (which may cause unexceptable delays to interrupts) or to disable the scheduler, which will perhaps hold off a high priority task needlessly.

What is your problem with using a mutex?

FreeRTOS: Memory Management

Posted by paulromero on May 25, 2016

Hi Richard:

I have no problem, and actually like, using mutexes. However, some folks complain that they degrade performance.

Best Regards,

Paul R.

FreeRTOS: Memory Management

Posted by rtel on May 25, 2016

On the assumption the allocation is going to be fast, and taking your point that nobody should be doing this in an interrupt (although you would be surprised what people do ;o) I would second Richard D's suggestion of suspending the scheduler.

// Do you thing here

It might be that you do not need to do this around the entire allocation function, but just at select points within the algorithm where simultaneous access would be an issue.

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