AVC_FUNCTION_COMMAND
The AVC_FUNCTION_COMMAND function code is used to send an AV/C request and receive a response as one operation.
I/O Status Block
If successful, the AV/C protocol driver sets Irp->IoStatus.Status to STATUS_SUCCESS.
Possible other return values include:
| Return Value | Description |
|---|---|
| STATUS_TIMEOUT | The request was made, but no response was received before all time-out and retry processing was complete. The target device ignores requests if a previous request is still being processed. Some AV/C devices are noncompliant, and refuse to respond within the 100-ms time-out, even after several successive attempts. The AVC_COMMAND_IRB structure permits the adjustment of the default Timeout and Retries members (100ms and 9, respectively), but these default settings have been sufficient for all known implementations. |
| STATUS_PENDING | The request was made, and an interim response was received. It is the responsibility of the completion routine to handle the final response and free the IRP and IRB resources. |
| STATUS_REQUEST_ABORTED | When submitting AV/C requests, immediately abort when the IRP completion status is STATUS_REQUEST_ABORTED. |
| STATUS_* | Any other return code indicates that an error or warning occurred that was beyond the scope of the AV/C protocol. |
Comments
This function uses the AVC_COMMAND_IRB structure as shown below.
typedef struct _AVC_COMMAND_IRB {
AVC_IRB Common;
UCHAR SubunitAddrFlag : 1;
UCHAR AlternateOpcodesFlag : 1;
UCHAR TimeoutFlag : 1;
UCHAR RetryFlag : 1;
union {
UCHAR CommandType;
UCHAR ResponseCode;
};
PUCHAR SubunitAddr;
PUCHAR AlternateOpcodes;
LARGE_INTEGER Timeout;
UCHAR Retries;
UCHAR Opcode;
ULONG OperandLength;
UCHAR Operands[MAX_AVC_OPERAND_BYTES];
NODE_ADDRESS NodeAddress;
ULONG Generation;
} AVC_COMMAND_IRB, *PAVC_COMMAND_IRB;
Requirements
Headers: Declared in avc.h. Include avc.h.
AVC_COMMAND_IRB Input
Common
The Function submember of this member must be set to AVC_FUNCTION_COMMAND from the AVC_FUNCTION enumeration.
SubunitAddrFlag
Set this to one to override the subunit address that avc.sys associates with the subunit driver. Reasons to override include: the subunit driver represents multiple subunits in a single instance; a unit command must be sent; or the driver was loaded because avc.sys could not determine the subunit type or ID. If this is set, the SubunitAddr member must point to nonpaged memory containing the desired subunit address.
This must be set to one (and the appropriate SubunitAddr supplied) if the caller is submitting requests directly to an avc.sys FDO.
Note
If this flag is not set on request, on response from a successful request, this flag is set, and the SubunitAddr member points to the actual address of the subunit. Do not attempt to alter the contents or free the memory: it is part of the parent driver's device extension. This may, of course, be set back to zero, and the SubunitAddr pointer cleared to reuse the structure for a different subunit.
AlternateOpcodesFlag Set this to one if the command type and opcode of this request results in a response with a different opcode. Without this, only responses with matching opcodes are accepted. If this is set, the AlternateOpcodes member must pointer to nonpaged memory containing the list of alternate opcodes.
TimeoutFlag
Set this to one if the default time-out is not appropriate for the subunit. If this is set, the Timeout member must be set to the desired time-out (in 100-ns units).
RetryFlag
Set this to one if the default retry count is not appropriate for the subunit. If this is set, the Retries member must be set to the desired retry count.
CommandType On request, this member must be set to one of the enumerators from the AvcCommandType enumeration. This is a required parameter.
ResponseCode On response, this member is set to a value from the AvcResponseCode enumeration.
SubunitAddr
Set this to the address of nonpaged memory containing the desired subunit address encoded according to Section 5.3.3 of the 1394 Trade Association AV/C Digital Interface Command Set General Specification, Rev 3.0. No length is necessary because the subunit address encoding implies this. This parameter is ignored if SubunitAddrFlag is zero.
AlternateOpcodes Set this to the address of nonpaged memory containing the desired alternate opcode list. The first byte of the opcode list is the count of opcodes to follow (equivalent to the number of bytes). The total length of the memory containing the alternate opcode list is AlternateOpcodes[0]+1. This parameter is ignored if AlternateOpcodesFlag is zero.
Timeout
Set this to the desired time-out in 100-ns units. For example, the default time-out value is: Timeout.QuadPart = 1000000 (100ms in 100ns units). This parameter is ignored if TimeoutFlag is zero.
Retries Set this to the desired number of times avc.sys should attempt to retry requests after each time-out without a response. Note that a retry count of zero means that the request is tried once. The total amount of time spent trying to process a command without getting a response is calculated by the following formula:
Timeout * (Retries+ 1)
This parameter is ignored if RetryFlag is zero.
Opcode Set this to the desired AV/C opcode (appropriate for the subunit type). This is a required parameter. On response, if AlternateOpcodesFlag was set, and one of the alternate opcodes was used to match the response, this is set to that alternate opcode.
OperandLength
Set this to the number of bytes used to store the operands in the Operands member. This is a required parameter. On response, this parameter is set to the number of bytes in the operand list used by the response.
Operands
Set this to the operand list appropriate for the subunit type and opcode. This is a required parameter. On response, this parameter contains the operand list of the response.
NodeAddress Reserved. This must be zero.
Generation
Reserved. This must be zero.
The AVC_FUNCTION_COMMAND function code is not supported by virtual instances of avc.sys. If the caller wishes to control an external device, that device's nonvirtual instance can be located through a private mechanism, or through some combination of the AVC_FUNCTION_FIND_PEER_DO, AVC_FUNCTION_PEER_DO_LIST and AVC_FUNCTION_GET_SUBUNIT_INFO function codes of the IOCTL_AVC_CLASS I/O control code.
This structure defines the common components of an AV/C command request. It holds the opcode and operands of a request, and the opcode and operands of a response (upon completion). The size of the operand list is fixed at the maximum allowable number of operands given a one-byte subunit address. If the subunit address is extended in any way, the maximum permissible number of operand bytes is reduced accordingly.
The recommended use of this structure is to first zero the structure (use RtlZeroMemory) before filling in the parameters.
This must be called at IRQL = PASSIVE_LEVEL.
See also
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