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Absolute address allocation specification (#pragma address)
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Declare #pragma address in the module in which the variable to be allocated in an absolute address is to be defined. Variables can be allocated to the arbitrary address.
[Function]
- | The specified variable is allocated to the specified address. |
[Effect]
- | Variables can be allocated to desired addresses. |
[Usage]
- | Declare #pragma address in the module in which the variable to be allocated in an absolute address is to be defined. |
#pragma address [(]variable-name=absolute-addressNote[,...][)]
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Note | Absolute-address : Effective address (binary, octal, decimal, or hexadecimal constant in
C language) |
[Restrictions]
- | #pragma address should be specified before declaration of the target variable. #pragma address after a variable declaration has no effect (no warning is output). |
- | If an object that is not a variable is specified, an error will occur. |
- | If #pragma address is specified for a const-qualified variable, an error will occur. |
#pragma address i=0xf2000
const int i = 0; //Error
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- | If #pragma address is specified for a variable declared with an initial value, an error will occur. |
#pragma address i=0xf2000
int i = 0; //Error
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- | If multiple #pragma address directives are specified for a single variable, an error will occur. |
#pragma address i=0xf2000
#pragma address i=0xf2000 //Error
int i;
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- | If a single address is specified for separate variables or the addresses allocated to separate variables overlap, an error will occur. |
- | If #pragma address is specified for a variable declared with __saddr, a compilation error will occur. |
#pragma address i=0xffe20
int __saddr i; //Error
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- | When #pragma address is declared for a variable that is explicitly or implicitly specified as near and if the specified absolute address is not in the range from 0x0F0000 to 0x0FFFFF, a compilation error will occur. |
#pragma address n_i1=0xF0000
char __near n_i1; //Can be compiled
#pragma address n_i2=0xEFFFF
char __near n_i2; //Error
#pragma address n_i3=0xEFFFF
char n_i3; //Error
//This is because bss is set to near regardless of
//whether -memory_model=small or medium
#pragma address f_i=0xEFFFF
char __far f_i; //Can be compiled
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[Example]
The following shows a sample C source code.
#pragma address (io=0x0ffe00)
int io; //io is allocated to address 0x0ffe00
func(void){
io = 0;
}
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Variables are declared and allocated to sections as follows in the assembly code.
.PUBLIC _io
.SECTION .bss, BSS
.ORG 0xFFE00
_io:
.DS 2
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The following code is output in the function.
clrw ax
movw !LOWW(_io), ax
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[Remark]
- | Even when #pragma address is specified, the volatile attribute is not automatically added to variables.
The -volatile option can add the volatile attribute to all static variables, including those with #pragma address.
To add the volatile attribute separately to certain variables, declare each variable with volatile appended. |
- | When allocating a variable to a specified address, consider alignment of the variable. Do not allocate a variable over a 64-Kbyte boundary. |