ZYNQ QNX開發——PL串口設備驅動遇到的問題

在ZedBoard上開發基於QNX操作系統PL部分UART設備驅動的過程中遇到了一點問題，問題原因不明但總結下來給大家提供參考，也以便以後對QNX的進一步瞭解後回顧這些問題。

硬件平臺：MIZ702完全兼容ZedBoard
HOST：Windows QNX Momentics IDE
功能：ZYNQ芯片的PL部分實現一路UART，並編寫QNX下設備驅動。

在讀串口時，申請了動態內存保存從串口讀到的數據，然後再填充IOV,返回給Client。代碼如下：

int io_read(resmgr_context_t *ctp,io_read_t *msg,RESMGR_OCB_T *ocb)
{
    int nleft;
    int nbytes;
    int nparts;
    int status;

    if((status = iofunc_read_verify(ctp,msg,ocb,NULL))!=EOK)
        return(status);
    if((msg->i.xtype &_IO_XTYPE_MASK)!= _IO_XTYPE_NONE)
        return (ENOSYS);

    char* buffer = (char *) malloc(msg->i.nbytes);
    memset(buffer,0,msg->i.nbytes);

    ocb->attr->nbytes = XUartLite_Recv(UartLite,buffer,msg->i.nbytes);
    nleft = ocb->attr->nbytes - ocb->offset;
    nbytes = min(msg->i.nbytes,nleft);
    printf ("receive %d bytes = '%s'  expected read %d \n", nbytes, buffer,msg->i.nbytes);

    if(nbytes>0)
    {
        //set up the return data IOV
        SETIOV(ctp->iov,buffer,nbytes);
        //set up the number of bytes (returned by client's read())
        _IO_SET_READ_NBYTES(ctp,nbytes);

        //advanced the offset by the number of bytes
        //returend to the client

        //ocb->offset +=nbytes;
        nparts = 1;
    }else
    {
        //they've asked for zero bytes or they've already previously read everythin
        _IO_SET_READ_NBYTES(ctp,0);
        nparts = 0;
    }

    //mark the access time as invalid (we just accessed it)
    if(msg->i.nbytes > 0)
        ocb->attr->flags |= IOFUNC_ATTR_ATIME;
    free(buffer);
    return(_RESMGR_NPARTS(nparts));
}

動態內存的大小是以read消息中期望讀到的數據長度來決定的，若用cat 命令讀取設備驅動信息 即

cat /dev/uartlite

系統會報錯：Server fault on msg pass
若在Client中用read讀 /dev/uartlite 則沒有問題，這個問題的原因是cat 中 read命令中的長度參數是32768，read函數中的長度沒有這麼大。

總結一下就是：動態申請的內存過大則會導致消息傳遞錯誤