我使用如下方法操作一个地址为0x56000020的端口
unsigned long
port_addr;
(void *)(port_addr) =
ioremap(0x56000020,0x8);
操作端口使用如下代码:
*(volatile unsigned
int*)(port_addr)|=0x00008000;
编译时出现warning,
(void *)(port_addr) =
ioremap(0x56000020,0x8);
warning: use of cast expressions as lvalues is
deprecated
左值为什么说有问题呢?
ioremap的定义明明是:
(void *)ioremap(unsigned long
offset, unsigned long size)
应该写成这样:
代码:
port_addr = (unsigned
long)ioremap(0x56000020, 0x8)
C语言的基本问题:
编译警告中说,对左值的强制转换写法是过时的:
不过既然头文件中的函数声明是
代码:
(void *)ioremap(unsigned long offset, unsigned long size)
不如直接写:
代码:
volatile unsigned int *port_addr = ioremap(0x56000020,0x8);
*port_addr |= 0x00008000;
ANSIC(C89)和C99的规范都允许空指针与其它指针的任意转换。
#define rGPACON (*(volatile unsigned *) (ioremap(GPACON,0x8)))