Difference between revisions of "Const and volatile type qualifiers"
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=Memorymapped access to a register= | =Memorymapped access to a register= | ||
==Example 1== | ==Example 1== | ||
| − | In the example below the register 32 bit register located in memory at address 0x40000 can be accessed through the uartreg pointer. | + | In the example below the register 32 bit register located in memory at address 0x40000 can be accessed through the ''uartreg'' pointer. |
<source lang=c> | <source lang=c> | ||
Revision as of 11:05, 31 August 2011
const
const means that something is not modifiable, so a data object that is declared with const as a part of its type specification must not be assigned to in any way during the run of a program.
volatile
The use of volatile ensures that the compiler always carries out the memory accesses, rather than optimizing them out (for example if the access is in a loop).
Memorymapped access to a register
Example 1
In the example below the register 32 bit register located in memory at address 0x40000 can be accessed through the uartreg pointer.
unsigned int volatile * const uartreg = (unsigned int *) 0x40000;
*uartreg |= 0x80881119;