viMemAlloc/viMemAllocEx
Purpose
Allocates memory from a resource's memory region.
C Syntax
ViStatus viMemAlloc(ViSession vi, ViBusSize size, ViPBusAddress offset)
ViStatus viMemAllocEx(ViSession vi, ViBusSize size, ViPBusAddress64 offset)
Visual Basic Syntax
viMemAlloc&(ByVal vi&, ByVal size&, offset&)
Resource Classes
GPIB-VXI INSTR, PXI MEMACC, VXI INSTR
Parameters
| Name | Direction | Description |
|---|---|---|
|
vi |
IN |
Unique logical identifier to a session. |
|
size |
IN |
Specifies the size of the allocation. |
|
offset |
OUT |
Returns the offset of the allocated memory. For viMemAlloc(), this is a 32-bit value for 32-bit applications and a 64-bit value for 64-bit applications. For viMemAllocEx(), this is always a 64-bit value. |
Return Values
| Completion Codes | Description |
|---|---|
|
VI_SUCCESS |
Operation completed successfully. |
| Error Codes | Description |
|---|---|
|
VI_ERROR_INV_OBJECT |
The given session reference is invalid. |
|
VI_ERROR_NSUP_OPER |
The given vi does not support this operation. |
|
VI_ERROR_RSRC_LOCKED |
Specified operation could not be performed because the resource identified by vi has been locked for this kind of access. |
|
VI_ERROR_INV_SIZE |
Invalid size specified. |
|
VI_ERROR_ALLOC |
Unable to allocatte shared memory block of the requested size. |
|
VI_ERROR_MEM_NSHARED |
The device does not export any memory. |
Description
The memory region referenced by the offset returned from viMemAlloc() can be accessed with the high-level operations viMoveInXX() and viMoveOutXX(), or mapped using viMapAddress(). When using viMemAllocEx(), the offset returned may be accessed by the viMoveInXXEx() and viMoveOutXXEx() operations, and mapped using viMapAddressEx(). Note that for viMemAllocEx(), the offset could be above the 4 GB boundary. If your device cannot access this memory, you should use viMemAlloc() instead.
VXI/GPIB-VXI INSTR Specific
Notice that the offset parameter to these operations for an INSTR Resource is the offset address relative to the device's allocated address base. The viMemAlloc() and viMemAllocEx() operations return an offset into a device's memory region allocated for use by this session. If the device to which the given vi refers is on the local interface card, the memory can be allocated either on the device itself or on the computer's system memory.
PXI/PCI MEMACC Specific
For a MEMACC Resource, the offset parameter specifies an absolute address. This is a physical address in system memory and can be used for device DMA.
Related Topics
viMoveIn8/viMoveIn16/viMoveIn32/viMoveIn64, viMoveIn8Ex/viMoveIn16Ex/viMoveIn32Ex/viMoveIn64Ex