为了寻找ping-pong操作样例，搜VisualDSP自带的代码例子，在 Blackfin\Examples\ADSP-BF533 EZ-KIT Lite\AD9244 ADC (C)\main.c中有如下一段代码，从注释看好像是说信号量能够使得程序等待，例子程序中也没有判断dma数据已经操作过的代码，但我测试下来并不能等待。

请问，如何利用semphore 挂起程序等待中断？

Software:               VisualDSP++4.5

Hardware:                BF533 EZ-KIT Board    Rev 1.1
                        Extender Card    Rev. 1.3
                        AD9244 Evaluation Board

#include "system.h"
#include "sysreg.h"
#include "ccblkfn.h"

// semaphore to indicate that a half has been transmitted
short DMA_completed_Receive = 0;

// store IMAKS register when interrupts are disabled
int interruptLatch;

    Ping_Pong = 0;
    DMA_completed_Receive = 0;

     // configure the programmable flags (for debug)
    //initFlags();
    
    // initialise Hardware
    //InitPPI();                    // enable PPI (will start only after an impulse on PF2)
    //InitInterrupts();
int x=0;

// MAIN loop
    // waits indefinetely for interrupts from DMA                   这句话是说会在信号量上持续等待吧？
    // When an interrupt has occured, the flag indicates which half of the received data the main loop can process
    while(1) {

// sync to interrupt through semaphore
        asm("cli %0;" : "=d" (interruptLatch)); asm("ssync;");
        // Check for the semaphore, and process if semaphore indicates completion
        if (DMA_completed_Receive == 1)  {
                DMA_completed_Receive = 0;     // reset the semaphore
        }    // if

        asm("sti %0;" : : "d" (interruptLatch)); asm("ssync;");

        // insert interruptible code here
        //    variable Ping_Pong indicates which half is "free"
        // for instance: copy to buffer for display              这里面没有判断已经处理过，不需要再次处理的代码

        *pFIO_FLAG_S = 0x0001;                        // PF0 shows execution time of this loop
        for (i=(Ping_Pong * Number_of_ADC_channels * Number_of_Samples); i<(((Ping_Pong+1) * Number_of_ADC_channels * Number_of_Samples)); i++)
            ADC_data[i] = sPPI_RxBuffer[i];

        printf("%d ",x++); //我增加这段代码，注释掉中断函数中的DMA_completed_Receive = 1;注释掉main()中的//initFlags();//InitPPI();//InitInterrupts();调用，仍然会持续不断的吐数据，证明程序没有挂起等待 (最上面注释中说的 waits indefinetely for interrupts from DMA）

        *pFIO_FLAG_C = 0x0001;                        // PF0 shows execution time of this loop
        
        
    }          

}

输出：

    Load complete.
    0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66.....

多谢andy！