Thanks Anonymonk, the bytes most definitely have individual meaning... MSByte is a control register (which actually consists of two 4-bit nibbles, but I dissect that later in the chain), and LSByte is the data register, both of a larger 16-bit command register, which gets sent to a piece of hardware over the Serial Peripheral Interface.

Example of what I was originally toying with:

# perl

testing(65535, 4);

...

// C

#include <stdio.h>

int testing(int n, int len){

    unsigned char bytes[4];

    bytes[3] = (n >> 24) & 0xFF;
    bytes[2] = (n >> 16) & 0xFF;
    bytes[1] = (n >> 8)  & 0xFF;
    bytes[0] = n & 0xFF;
    
    printf("output should be 255, 255, 0, 0\n\n"); 
    printf("%d, %d, %d, %d\n", bytes[0], bytes[1], bytes[2], bytes[3])
+;

    return 0;
}

[download]

Works fine. The problem though is that the buf array is eventually sent to another C function that puts it on the SPI bus. The way I've done it in the above example limits me to accept/send only a single 4-byte array, so if a device requires say 6 bytes, I'd have to add in another param (at least that's how I saw it). I wanted my Perl code to be as compatible with the API I'm using as possible, and heck, I've always wanted to learn how to pass in an array/aref to a C function anyway, so it was a fun learning experience :)

In reply to Re^2: Is this a sane/safe way to pass an aref into a C function? by stevieb
in thread Is this a sane/safe way to pass an aref into a C function? by stevieb

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