/*示例*/
extern volatile char UART1_SR;
#pragma required=UART1_SR
char sFlag;
void Foo(void)
{
while (!sFlag)
{
    asm(" ldr r2,[pc,#0] \n"        /* r2 = address of sFlag */
    " b .+8 \n"                     /* jump over constant */
    " DCD sFlag \n"                 /* address of sFlag */
    " ldr r3,[pc,#0] \n"
 
            /* r3 = address of UART1_SR */
    " b .+8 \n"                     /* jump over constant */
    " DCD UART1_SR \n"              /* address of UART1_SR */
    " ldr r0,[r3] \n"               /* r0 = UART1_SR */
    " str r0,[r2]");                /* sFlag = r0 */
}
}