ADS1.2中的内建变量（转）

ARM9 SC2440和2410得初始化代码中有下面一个定义:
GBLL    THUMBCODE
   [ {CONFIG} = 16
THUMBCODE SETL  {TRUE}
         CODE32
   |
THUMBCODE SETL  {FALSE}
   ]      

网上的朋友有问下面问题的，我也有疑惑，从ARM官方网站查到了答案。特此列出。

请问代码里的 {CONFIG} 代表什么含义，如何知道它是不是等于为16

是某处定义的某个变量？

还是编译的时候某个配置选项？

Built-in variables and constants
Table 3.3 lists the built-in variables defined by the ARM assembler.
Table 3.3. Built-in variables
{ARCHITECTURE}
 Holds the name of the ARM architecture selected by the --device option.
 
{AREANAME}
 Holds the name of the current AREA.
 
{ARMASM_VERSION}
 Holds an integer that increases with each version of armasm.
 
|ads$version|
 Has the same value as {ARMASM_VERSION}.
 
{CODESIZE}
 Is a synonym for {CONFIG}.
 
{COMMANDLINE}
 Holds the contents of the command line.
 
{CONFIG}
 Has the value 32 if the assembler is assembling ARM code, or 16 if it is assembling Thumb code.
 
{CPU}
 Holds the name of the CPU selected by the --device option.
 
{ENDIAN}
 Has the value “big” if the assembler is in big-endian mode, or “little” if it is in little-endian mode. The default value is selected by the --device option.
 
{FPU}
 Holds the name of the FPU. The default FPU name is selected by the --device option.
 
{INPUTFILE}
 Holds the name of the current source file.
 
{INTER}
 Has the boolean value True if /inter is set. The default is False.
 
{LINENUM}
 Holds an integer indicating the line number in the current source file.
 
{OPT}
 Value of the currently-set listing option. The OPT directive can be used to save the current listing option, force a change in it, or restore its original value.
 
{PC} or .
 Address of current instruction.
 
{PCSTOREOFFSET}
 Is the offset between the address of the STR pc,[…] or STM Rb,{…, pc} instruction and the value of pc stored out. This varies depending on the device specified.
 
{ROPI}
 Has the boolean value True if /ropi is set. The default is False.
 
{RWPI}
 Has the boolean value True if /rwpi is set. The default is False.
 
{VAR} or @
 Current value of the storage area location counter.
  
Built-in variables cannot be set using the SETA, SETL, or SETS directives. They can be used in expressions or conditions, for example:
        IF {ARCHITECTURE} = "4T"
The built-in variable |ads$version| must be all in lowercase. The names of the other built-in variables can be in uppercase, lowercase, or mixed. For example:
        IF {CpU} = "ARM7TDMI"
Note
All built-in string variables contain case-sensitive values. See CPU names for valid values for {CPU} and {ARCHITECTURE}. See FPU names for valid values for {FPU}. Relational operations on these built-in variables will not match with strings that contain an incorrect case.
Table 3.4 lists the built-in Boolean constants defined by the ARM assembler.
Table 3.4. Built-in Boolean constants
{FALSE}
 Logical constant false.
 
{TRUE}
 Logical constant true.