Synchronous +Requests

<b>Synchronous +requests</b>

Synchronous requests are typically used to set +or retrieve some information for the device driver. These requests almost +never need to access the hardware itself, and usually complete relatively +quickly. They return only after the completion of the request and the user +side thread is blocked till completion. Synchronous requests are usuallly +initiated by a call to RBusLogicalChannel::DoControl(). +The request is most likely to be executed in the context of the client user-side +thread.

A driver lists its available synchronous requests +in an enumeration, for example:

// Synchronous control messages used with DoControl() +enum TControl + { + EControlConfigure, // Configure the device (UART) + EControlTransmitData, // Transmit data over the device (UART) + EControlReceiveData, // Receive the data from the device + ENumRequests, // Number of synchronous control requests + AllRequests = (1<<ENumRequests)-1 + };

Implementation

Drivers +generally implement the DoControl() function in the LDD +to handle the received synchronous messages. The implementation reads the +request type and other passed arguments, and handles the request appropriately. +For example, the following handles RExDriver::EControlConfigure requests:

TInt DExDriverLogicalChannel::DoControl(TInt aFunction, TAny* a1, TAny* /*a2*/) + { + switch (aFunction) + { + case RExDriver::EControlConfigure: + memclr(&c, sizeof(c))); + TPtr8 cfg((TUint8*)&c, 0, sizeof(c))); + r = Kern::ThreadDesRead(iClient,a1,cfg,0,0); + if (r==KErrNone) + Pdd()->Configure(&c); + break; + ... + default: + r = KErrNotSupported; + } + return r; + }