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