Use for Memory allocation?

AppleDavidJeans · August 17, 2016, 9:31am

So I saw this thread: https://vexforum.com/t/how-to-use-malloc-or-free-in-robotc/36036/1

I know that ROBOTC does not support malloc, but jpearman posted a library for one. I’m curious as to how that would be useful.

Team80_Giraffes · August 17, 2016, 10:13am

The BNS library wanted to have a dynamic sized array for some of their items. So they implemented their own malloc looking for contiguous memory block sizes available to store their stuff. If memory is available, they claim it for you. They have also implemented some defragmenting routines too to clean up after themselves.

It’s pretty clever.

You can look at their BNS malloc routine in here:

github.com

JMarple/BNSLibrary/blob/master/Modules/Core/BNSHeap.c

// BNSHeap.c
//
// Author: Justin Marple with Team BNS
// Contact: [email protected]
// Date: 12/18/2014
//
// This source file includes source code that
// implements a memory heap for use in
// Vex Robotics Competition.  These operations
// include:
//  - bnsMalloc
//  - bnsFree
//  - bnsGetHeapElement
//  - bnsSetHeapElement
// This heap is implemented by setting the size
// of each "chunk" as the first element.  The
// data is then every consecutive element in that
// chunk-size. Traverseing the heap requires you
// to start from the initial chunk and increase
// the heap location by the size of that chunk

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The malloc is used by their matrix functions for dynamic sizes which is used by their matrix math functions which is used by their filters. This way you don’t make a fixed number of items in your filter, the code will manage just the size you need. There will be an upper limit though. Not sure what that is.

system · January 3, 2020, 9:42pm