SDIO Host Controller Driver Fast-Path Support
Other versions of this page are also available for the following:
.gif "A hyphen indicates that the information in this topic is not relevant for this platform, or that the platform does not support the API that is listed.")
.gif "A checkmark indicates that the information in this topic is relevant for this platform, and that any API listed is also supported on this platform.")
8/28/2008
The primary change to the host controller driver is the addition of polling for Fast-Path operations. A normal SDIO operation utilizes interrupts after I/O starts on the controller. Fast-Path requires the host controller driver poll for I/O completion instead. For more information on Fast-Path operations, see SDIO Fast-Path Overview.
Checking for Fast-Path Support
Even though the bus driver is responsible for enabling Fast-Path, the host controller driver determines whether or not to perform Fast-Path operations. The host controller driver can determine if Fast-Path operations are enabled by using the following code.
BOOL bFastPathEnabled;
//Determine if Fast-Path is enabled for this request.
bFastPathEnabled = ( 0 != ( pRequest->SystemFlags & SD_FAST_PATH_AVAILABLE));
Note
After the host controller driver ascertains if Fast-Path is enabled, it needs to determine if Fast-Path is the optimal method for handling the bus request.
Fast-Path Threshold
The host controller driver compares the size of a bus request against a threshold value to determine whether or not a bus request should proceed as a Fast-Path operation. The threshold value ensures that bus requests proceed as Fast-Path operations when doing so will speed up the processing of the request and will not degrade system throughput. By default, the Fast-Path threshold is set at 2 kB. The following registry entry can be used to change the default threshold by editing the Threshold value.
[HKEY_LOCAL_MACHINE\Drivers\Builtin\SDBusDriver]
"Order"=dword:15
"Dll"="SDBus.dll"
"Prefix"="SDC"
"ThreadPriority"=dword:64 ; default thread priority for dispatch thread
"RequestListDepth"=dword:30 ; pre-allocated requests
"Flags"=dword:10000 ; DEVFLAGS_TRUSTEDCALLERONLY
"IClass"=multi_sz:"{20FA98A8-B298-4b32-8D72-C716AEE2FA84}=%b","{6F40791D-300E-44E4-BC38-E0E63CA8375C}=%b"
"Threshold”=dword:0x800