10 years, 3 months ago.

Hello again Antreas!

After looking at the specs for the LPC11U24 I realized that the internal SRAM is a little on the small size compared to what I'm used to working with - so you very well might be looking at an out-of-memory issue. The bottom-line is that you have either 8 or 10 kb of ram, 2kb of which is reserved for internal use; so 6kb (LPC11U24FHI33/301) or 8kb (LPC11U24FBD48/401).

How much your array can hold depends on how you're implementing the array. Here are a few situations:

Simple array

...
float myFloats[1000]; 
// (4bytes)(1000 myStructs) = 4000 bytes / 1024 byes/kb = 3.9 kb
// ...which is probably fine, but you would have to be careful when using memory elsewhere
// to be safe, use this to reserve that memory upon program entry:
// float *myFloats = new float[1000];

Using array of structs (all initialized once declared)

struct myStruct {
int someInt;  // Either 2 bytes or 4 bytes, depending on the mbed library.
float someFloat; // 4 bytes.
};
...
myStruct data[1000]; // Worst case: (4bytes+4bytes)(1000 myStructs) >= 8kb -- which would instantly overrun both chips

My recommendation:

#include "darray.h" // see below for library info
...
darray<float> myArray;
myArray.reserve(500); // Go ahead and reserve 500 floats since we know we'll need a lot (4bytes)(500 floats) = 2.05 kb
...
myArray.pushback(someFloat); 
// Will use the memory reserved for the 500 floats then expand the array at a size of 5 floats each time it runs out of space
// Once the target is out of memory, it fails a cassert rather than trying to write to reserved memory space.

I've went ahead and published my darray library incase you want to try that solution out: DynamicArrays

However, these solutions don't really solve the main problem of working with low SRAM, and if you really need a buffer that size, you will need to do something like run two large buffers and delete[] one once you're close to running out of memory. Another option is to use mbed's filesystem library to store those values into the on-board flash memory. The speed at which this would work kind of defeats the purpose of a buffer, but it would be satisfactory if you're just doing some basic data-logging.

Hope that helps :)