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I have a three-dimensional array of binary numbers, which I use as a dictionary and pass through an LED array. The dictionary covers 27 letters, and each letter covers 30x30 pixels (where each pixel is a 0 or a 1).

I was using the Intel Edison - and the code worked well - but I ditched the Edison after having trouble connecting it to my PC (despite replacing it once). I switched to the Arduino Uno, but am now receiving an error that the array is too large.

Right now I have the array set as boolean. Is there anyway to reduce the memory demands of the array by setting it instead as bits? The array consists of just zeros and ones.

Here's a snip of the code:

boolean PHDict[27][30][30] = {  
/* A */ {{ 0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  1,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0}, /* this is one column of thirty, that show "A" as a letter */
Mark Sperling
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1 Answers1

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You could write it as

#include <stdint.h>

//...

uint32_t PHdict[27][30] = {
{ 0x00004000, ... },
....
};

.. Where each entry contains 30 bits packed into a 32-bit number. The size is under 4k bytes.

You would need a bit of code to unpack the bits when reading the array, and a way to generate the packed values (I.e a program which runs on your "host" computer, and generates the initialized array for the source code)

For the AVR processor, there's also a way to tell the compiler you want the array stored in PM (Flash memory) instead of DM - I think if you have it in DM, the compiler will need to put the initialization data in PM anyway, and copy it over before the program starts, so it's a good idea to explicitly store it in PM. See https://gcc.gnu.org/onlinedocs/gcc/AVR-Variable-Attributes.html#AVR-Variable-Attributes

In fact, depending on the amount of flash memory in the processor, changing it to PM may be sufficient to solve the problem, without needing to pack the bits.

greggo
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