Wince上USB host 中U盘兼容性问题点滴

我们现在使用的是sirfA4芯片做的产品，使用它的USB口用于U盘读播MP3和视频文件，之前发现USB口出现这样问题：有个次品U盘（标称容量16G，实际容量只有4G），在电脑上都能正常读写数据，没有什么问题，但是拿到我们机器上就出现插入U盘可以识别，但是会经常性的出现读数据失败，USB识别到断开的情况。

追踪程序发现读取Csw 长度为0，此时会重新初始化，造成USB disk重新枚举，但是怎么也不能再读到U盘的数据，只有重新拔插才能正常工作。偶然机会发现，在读U盘数据时如果没有运行其他程序，出错的几率会小很多，于是判断是对USB的响应中出现了中断去做其他事情造成不能及时相应，兼容性不好的U盘就会死机，所以出现问题，只要及时响应USB操作，应该能解决此问题。最后在 disK.C中增加以下代码解决此问题：

       case DISK_IOCTL_WRITE:
        {
            DEBUGMSG(ZONE_DSK_IOCTL, (TEXT("USBDISK6>DSK_IOControl>%s\r\n"),
                (bRead ? TEXT("IOCTL_DISK_READ"):TEXT("IOCTL_DISK_WRITE"))));
            // Sterilize the caller's SG_REQ.
            if (!SterilizeIoRequest(
                pDevice->pSterileIoRequest,
                (PSG_REQ)pInBuf,
                InBufLen)
            ) {
                dwErr = ERROR_INVALID_PARAMETER;
                break;
            }
            // If write, ensure that the device is not write-protected.
            if (!bRead && pDevice->Flags.WriteProtect) {
                dwErr = ERROR_WRITE_PROTECT;
                break;
            }
            pDevice->Flags.MediumChanged = FALSE;
            // Initiate I/O. Note that, to determine if ScsiRWSG succeeded,
            // we are required to inspect the sr_status. It's safe to do so,
            // because pSterileIoRequest is our safe copy of the caller's
            // SG_REQ.
#if MXcompatible
            dwThreadID = GetCurrentThread();
    dwThreadPri = CeGetThreadPriority(dwThreadID);
    dwThreadQuantum = CeGetThreadQuantum(dwThreadID);
   CeSetThreadPriority(dwThreadID, 0);
        CeSetThreadQuantum(dwThreadID, 0);

try
{
#endif
            SafeBytesReturned = ScsiRWSG(
                pDevice,
                pDevice->pSterileIoRequest,
                pDevice->Lun,
                bRead
                );
#if MXcompatible
}
except(GetExceptionCode() == EXCEPTION_ACCESS_VIOLATION ?
    EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH)
{
      dwErr = pDevice->pSterileIoRequest->sr_status;
   CeSetThreadQuantum(dwThreadID, dwThreadQuantum);
  CeSetThreadPriority(dwThreadID, dwThreadPri);
   break;

}

            CeSetThreadQuantum(dwThreadID, dwThreadQuantum);
   CeSetThreadPriority(dwThreadID, dwThreadPri);
#endif

Wince上USB host 中U盘兼容性问题点滴

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