Defining relocatable sections in a source file

Define a relocatable section using the SECTION directive. See the following listing for an example of defining relocatable sections.

Listing: Defining relocatable sections containing data


constSec: SECTION   ; Relocatable constant data section.
cst1:     DC.B  $A6

cst2:     DC.B  $BC

dataSec:  SECTION   ; Relocatable data section.

var:      DS.B  1

In the previous portion of code, the label cst1 will be located at an offset 0 from the section constSec start address, and label cst2 will be located at an offset 1 from the section constSec start address. See the following listing:

Listing: Assembler Output


  2    2                     constSec: SECTION ; Relocatable
  3    3   000000 A6         cst1:     DC.B    $A6

  4    4   000001 BC         cst2:     DC.B    $BC

  5    5

  6    6                     dataSec:  SECTION ; Relocatable

  7    7   000000            var:      DS.B   1

Locate program assembly source code in a separate relocatable section, as listed in the following listing:

Listing: Defining a relocatable section for code


         XDEF  entry
codeSec: SECTION     ; Relocatable code section.

entry:

         LDA   cst1  ; Load value in cst1

         ADD   cst2  ; Add value in cst2

         STA   var   ; Store in var

         BRA   entry

In the previous portion of code, the LDA instruction is located at an offset 0 from the codeSec section start address, and ADD instruction at an offset 3 from the codeSec section start address.

In order to avoid problems during linking or execution from an application, an assembly file should at least:

Initialize the stack pointer if the stack is used
The RSP instruction can be used to initialize the stack pointer to $FF.
Publish the application's entry point using the XDEF directive.