Difference between revisions of "Const and volatile type qualifiers"
From Teknologisk videncenter
m (→Links) |
m |
||
| Line 6: | Line 6: | ||
=Memorymapped access to a register= | =Memorymapped access to a register= | ||
==Example 1== | ==Example 1== | ||
| − | In the example below the register 32 bit register located at address 0x40000 can be accessed | + | In the example below the register 32 bit register located at address 0x40000 can be accessed through the |
| + | |||
| + | <source lang=c> | ||
| + | |||
| + | unsigned int volatile * const uartreg = (unsigned int *) 0x40000; | ||
| + | *uartreg |= 0x80881119; | ||
| + | </source> | ||
=Links= | =Links= | ||
*[http://publications.gbdirect.co.uk/c_book/chapter8/const_and_volatile.html Const and volatile] | *[http://publications.gbdirect.co.uk/c_book/chapter8/const_and_volatile.html Const and volatile] | ||
Revision as of 10:09, 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 at address 0x40000 can be accessed through the
unsigned int volatile * const uartreg = (unsigned int *) 0x40000;
*uartreg |= 0x80881119;