DDCMDEntryPoint
The DDCMDEntryPoint function provides the interface through which device driver stream handlers communicate with the hardware Physical Device Driver (PDD).
Syntax
#include <os2.h> ULONG DDCMDEntryPoint(PDDCMDCOMMON pCommon);
Parameters
- pCommon (PDDCMDCOMMON) - input
- A pointer to a DDCMD message-specific input parameter block. This structure contains the function code and specific data required for the command being issued. See DDCMDCOMMON for the base structure.
Return Value
- rc (ULONG) - returns
- Return codes indicating success or the type of failure:
- NO_ERROR: Successful.
- ERROR_INVALID_FUNCTION: The function requested is not supported by the PDD.
- FAILURE: A DDCMD message-specific error return code was encountered.
Remarks
Stream handlers use the DDCMDEntryPoint to request that a PDD perform hardware-level operations, such as starting, stopping, or resuming device activity.
This interface utilizes the **Inter-Device Communication (IDC)** mechanism. To use this entry point, the stream handler must first perform the following steps:
- Call the ATTACHDD Device Helper (DevHelp) function.
- Obtain the IDC entry point address for the target Physical Device Driver.
- Use that address to issue Device Driver Command (DDCMD) messages.
Example Code
The following snippet shows the general pattern of calling a PDD entry point once the address has been obtained via IDC.
#include "os2.h"
#include "os2me.h"
ULONG rc;
PDDCMDCOMMON pDDCMD;
PFN pfnDDCMDEntryPoint; /* Address obtained via ATTACHDD */
/* ... Assume pfnDDCMDEntryPoint is initialized and pDDCMD is populated ... */
/* Invoke the PDD command entry point */
rc = pfnDDCMDEntryPoint(pDDCMD);
if (rc != NO_ERROR) {
/* Handle PDD-specific error */
}