Lpc2000

There are two types of constants with ARM: rodata and literal pools.

The rodata is used for stuff marked "const" in C, and the literal 
pool is used for large immediate values.

Consider the code:

const char hello[] = "hello";

void fn(void)
{
x = 5;

y = 0x12345678;
}

hello is stored in rodata

The 5 in x = 5 is small enough that this can fit in an immediate 
value and will compile to something like:

   mov   r4,#5

The value 0x12345678 is too large to store in an immediate 
instruction so the emmittted code becomes something like:


   ldr   r4,[pc,xxxx]
...
    .word 0x12345678

The actual data for 0x12345678 is stored as a literal value in 
the .text section along with the code and is loaded indirectly using 
the offset from the pc. This is called a literal pool.

BTW The assembler will do this for us automatically. All you need to 
do is write:

   ldr r4,=0x12345678

The assmebler will look at the value and determine if it can be done 
with a mov. If not then a suitable literal pool is made.