Syntax

symbol  .usect "section name", size in words[, blocking flag[, alignment] ]

Description

The .usect directive reserves space for variables in an uninitialized, named section. This directive is similar to the .bss directive (see .bss topic); both simply reserve space for data and that space has no contents. However, .usect defines additional sections that can be placed anywhere in memory, independently of the .bss section.

• The symbol points to the first location reserved by this invocation of the .usect directive. The symbol corresponds to the name of the variable for which you are reserving space.
• The section name must be enclosed in double quotes. This parameter names the uninitialized section. A section name can contain a subsection name in the form section name : subsection name.
• The size in words is an expression that defines the number of words that are reserved in section name.
• The blocking flag is an optional parameter. If you specify a value greater than 0 for this parameter, the assembler allocates size in words contiguously. This means that the allocated space does not cross a page boundary (64 words) unless its size is greater than a page, in which case the allocated space starts on a page boundary. By default, the compiler causes this flag to be set to 0 so that DP load optimization is used. The compiler provides the "blocked" and "noblocked" variable attributes for controlling blocking on a per-variable basis. For examples of DP load optimization, see the Tools Insider blog in TI's E2E community.
• The alignment is an optional parameter . It causes the assembler to allocate the specified size in words on long word boundaries. The resulting alignment will be on a boundary that is 2 to the power of the specified alignment parameter. For example, an alignment parameter of 5 gives an alignment of 2**5, which is 32 words.

Initialized sections directives (.text, .data, and .sect) tell the assembler to pause assembling into the current section and begin assembling into another section. A .usect or .bss directive encountered in the current section is simply assembled, and assembly continues in the current section.

Variables that can be located contiguously in memory can be defined in the same specified section; to do so, repeat the .usect directive with the same section name and the subsequent symbol (variable name).

For more information about sections, see Chapter 3.

Example

This example uses the .usect directive to define two uninitialized, named sections, var1 and var2. The symbol ptr points to the first word reserved in the var1 section. The symbol array points to the first word in a block of 100 words reserved in var1, and dflag points to the first word in a block of 50 words in var1. The symbol vec points to the first word reserved in the var2 section.

Figure 6-7 shows how this example reserves space in two uninitialized sections, var1 and var2.

       1           *******************************************
       2           **    Assemble into .text section.       **
       3           *******************************************
       4 000000           .text
       5 000000 9A03      MOV     AL, #03h
       6              
       7           *******************************************
       8           **    Reserve 1 word in var1.            **
       9           *******************************************
      10 000000      ptr  .usect  "var1", 1
      11              
      12           *******************************************
      13           **    Reserve 100 words in var1.         **
      14           *******************************************
      15 000001    array  .usect  "var1", 100
      16              
      17 000001 9C03      ADD     AL, #03h ; Still in .text
      18              
      19           *******************************************
      20           **    Reserve 50 words in var1.          **
      21           *******************************************
      22 000065    dflag  .usect  "var1", 50
      23              
      24 000002 08A9      ADD     AL, #dflag  ; Still in .text
         000003 0065-
      25              
      26           *******************************************
      27           **    Reserve 100 words in var2.         **
      28           *******************************************
      29 000000     vec  .usect  "var2", 100
      30              
      31 000004 08A9      ADD     AL, #vec  ; Still in .text
         000005 0000-
      32              
      33           *******************************************
      34           **    Declare an external .usect symbol  **
      35           *******************************************
      36                  .global array

Figure 5-7 The .usect Directive