Data Addressing. NXP CodeWarrior Development Studio

Data Addressing

21.3 Data Addressing

In absolute addressing, the compiler generates two instructions to fetch the address of a

variable. For example the compiler translates Listing 21-1 on page 372

into the instructions in

Listing 21-2 on page 372 .

Listing 21-1. Source Code

int red; int redsky; void sky()

{

red = 1;

redsky = 2;

}

Listing 21-2. Generated Code

li r3,1 lis r4,red@ha addi r4,r4,red@l stw r3,0(r4) li r5,2 lis r6,redsky@ha addi r6,r6,redsky@l stw r5,0(r6)

Each variable access takes two instructions and a total of four bytes to make a simple assignment. If you set the small data threshold to be at least the size of an int

data type, the compiler generates instructions to fetch variables with one instruction (

Listing 21-3 on page 372 ).

Listing 21-3. Fetching variables with one instruction

li r3,1 stw r3,red li r4,2 stw r4,redsky

Because small data sections are limited in size you might not be able to put all of your application data into the small data and small data2 sections. We recommend that you make the threshold as high as possible until the linker reports that you have exceeded the size of the section.

If you do exceed the available small data space, consider using pooled data.

Because the linker can not deadstrip unused pooled data, you should:

CodeWarrior Development Studio for Advanced Packet Processing Build Tools Reference Manual, Rev.

10.2, 01/2016

372 Freescale Semiconductor, Inc.