| Tag | Valid Values | Description |
| Type (OPTIONAL) | The exact string “Device”. The exact string “InternalBridge”. | This tag defines which other tags are expected. “Device” is used when the specified function acts as a normal PCI device. “InternalBridge” is used when the specified function is a bridge to additional devices on the same module. If Type is omitted, the function is assumed to be of type “Device”. |
| ModelCode | A 16-bit hexadecimal number. | This tag represents the PCI device ID of this function. |
| ManufCode | A 16-bit hexadecimal number. | This tag represents the PCI vendor ID of this function. |
| SubsystemModelCode (OPTIONAL) | A 16-bit hexadecimal number. | This tag represents the PCI subsystem ID of this function, if appropriate. This tag is REQUIRED if SubsystemManufCode is present. If specified, it implies that VISA should use the subsystem to identify the device. |
| SubsystemManufCode (OPTIONAL) | A 16-bit hexadecimal number. | This tag represents the PCI subsystem vendor ID of this function, if appropriate. This tag is REQUIRED if SubsystemModelCode is present. |
| VISARegistration (OPTIONAL if Type=Device, not applicable otherwise) | The exact string “None”. The exact string “Simple”. The exact string name of a VISA device registration information section. | This tag describes how to register this function with VISA. If not present, the value “None” is assumed, which means this function will not be registered with VISA (for example, because it already has a separate driver). If the value “Simple” is used, the device is registered using the default settings for the tags described in the VISA registration descriptor. Otherwise, it is registered using the information provided in the specified section. |
| DeviceList (if Type=InternalBridge, not applicable otherwise) | A list of comma-separated numbers. | This tag lists the PCI device numbers of devices found on this module behind this bridge. The device numbers in this list are fixed for a given module since the IDSEL lines between the bridge and its devices are fixed. |
# Module Descriptor Example
\# This example describes a function which is a normal PCI device at function 0 and # which should be registered with VISA
[Function0]
Type = "Device"
ModelCode = 0x1234
ManufCode = 0xABCD
VISARegistration = "Simple"
RULE: For functions of type InternalBridge, the DeviceList tag SHALL list all devices bridged by this function.
PERMISSION: The VISARegistration tag MAY be other strings besides those listed in order to allow vendor-specific extensions.
RULE: If a vendor’s PXI Resource Manager, VISA, or other tool does not recognize the VISARegistration tag and cannot find a corresponding VISA registration descriptor in the module description file, it SHALL treat the tag as if it had the value “None”.
RULE: If a VISARegistration tag specifies a name that conflicts with a vendor-specific extension, tools which use that vendor-specific extension SHALL perform the specified behavior of the VISARegistration tag and not the vendor-specific behavior.
OBSERVATION: A module containing multiple PCI-to-PCI bridges would be exceedingly rare. However, such modules are fully supported because each function descriptor which represents a PCI-to-PCI bridge can contain a list of device descriptors which can contain further function descriptors representing more bridges.
# 2.4 VISA Registration Descriptor
The VISA registration descriptor provides information needed to register the device with VISA. If a function descriptor specifies a VISARegistration tag for that function, it can provide as that tag’s value a string specifying a required separate descriptor of VISA registration information.
RULE: A module description file SHALL contain a unique VISA registration descriptor for each function descriptor that includes a custom VISARegistration tag.
RULE: A VISA registration descriptor SHALL be named according to the string given in the function descriptor’s VISARegistration tag. For example, if a function descriptor lists
“VISARegistration=MyFunctionRegistration”, the module description file SHALL include a VISA registration descriptor named “MyFunctionRegistration”.
RULE: Each VISA registration descriptor SHALL contain the following tags:
| Tag | Valid Values | Description |
| NumDetectSequences (OPTIONAL) | A non-negative integer. | This tag indicates whether the given function of the module can generate interrupts that should be handled by VISA, and if so, how many different detection mechanisms are required to determine if the function is asserting an interrupt condition. If this tag is omitted it is assumed to be 0, indicating that the function does not generate interrupts that are handled by VISA. |
| InterruptDetectX (if NumDetectSequences >0) | A quoted string in interrupt detect/quiesce format (see section 2.4.1). | This tag is required for each X in the range [0...NumDetectSequences-1]. Each value is a quoted text string describing a series of register reads, writes, and compares that will allow VISA to identify whether an interrupt condition is caused by the given function of the module. At least one sequence must be true if this function is interrupting. |
| InterruptQuiesce (OPTIONAL if NumDetectSequences >0) | A quoted string in interrupt detect/quiesce format. | This tag describes a series of register reads, writes, and compares that will cause the given PCI function to stop asserting the interrupt condition detected by an InterruptDetectX operation. If this tag is omitted and NumDetectSequences >0, an empty string is used. |
| ManufName (OPTIONAL) | A text string. | This tag gives the name of the vendor of this function, which will be used to identify the function to VISA (that is, VI_ATTR_MANF_NAME) where appropriate. If this tag is omitted, the ModuleVendor value from the module description section (see section 2.2 above) is used instead. |
| ModelName (OPTIONAL) | A text string. | This tag gives the name of this function, which will be used to identify the function to VISA (that is, VI_ATTR_MODEL_NAME) where appropriate. If this tag is omitted, the ModuleName value from the module description section (see section 2.2 above) is used instead. |
# VISA Registration Descriptor Example
\# This example registers a VISA device that can cause interrupts
[MyFunctionRegistration]
NumDetectSequences = 1
InterruptDetect0 = "C8 BAR0 0x1000 0x1 0x1;"
InterruptQuiesce = "W8 BAR0 0x1000 0x0;"
ModelName = "Interrupting Function"
ManufName = "PXISA"
PERMISSION: The InterruptQuiesce operation MAY be an empty string as long as the InterruptDetectX operation(s) inhibit(s) the interrupt condition as a side effect of detecting it (as for a Release On Register Access, or RORA, implementation).
RULE: The detect operation is always required for a function that may cause interrupts that will be handled by VISA, and SHALL NOT be empty if present.
OBSERVATION: The VISA device registration also requires the use of the PCI device and vendor IDs and possibly the PCI subsystem ID and subsystem vendor ID. These values are found in the function descriptor (section 2.3) which is the parent of the VISA registration descriptor.
OBSERVATION: All tags in the VISA registration descriptor are optional.
RULE: If a VISA registration descriptor is present, it SHALL contain at least one of the specified tags. If all of the default VISARegistration descriptor tag values are acceptable, the function descriptor SHALL use “Simple” as the VISARegistration tag value, and not provide a VISA registration descriptor.
# 2.4.1 Interrupt Detect/Quiesce String Format
The InterruptDetectX and InterruptQuiesce tags have values that specify PCI register reads, writes, and compares that allow VISA to determine if a particular interrupt condition is caused by this function and if so, to correctly cause the function to stop asserting the interrupt condition.
The interrupt detect/quiesce string format is a compact, human and program-readable list of simple PCI operations. Each sequence string is made up of one or more operations, which are defined as follows:
| Operation Syntax | Meaning |
| Wwidth space offset value | Perform a register write of width bits (8, 16, or 32) into PCI address space space (CFG, BARn) at offset offset with the value value. |
| Rwidth space offset | Perform a register read of width bits (8, 16, or 32) from PCI address space space (CFG, BARn) at offset offset. |
| Cwidth space offset mask value | Perform a register read of width bits (8, 16, or 32) from PCI address space space (CFG, BARn) at offset offset, mask the read value with mask, and compare the result to value. |
For the purpose of the InterruptDetectX tag, the entire sequence is considered “true” if and only if all compare steps in the sequence are true.
# Interrupt Detect Example
An example of an interrupt detect sequence string could be "W32 BAR0 0x00001830 0x00000000;C8 BAR0 0x00001002 0x01 0x01;". This would write offset 0x1830 in PCI base address space 0 with the 32-bit value zero, then read the 8-bit register at offset 0x1002 and check if the bit masked by 0x1 is set. If so, the sequence is true.
# Interrupt Quiesce Example
An example of an interrupt quiesce sequence string could be "W8 BAR0 0x00001002 0x02;". This would simply write the 8-bit register at offset 0x1002 in base address space 0 with the value 0x02, which must stop the associated device from interrupting. Note that the interrupt condition need not be completely handled at this point—a VISA callback can be installed to do further handling once the interrupt is squelched.
RULE: Operations in a sequence SHALL be separated by semicolons and the list SHALL be terminated by a semicolon. Tokens within the operations SHALL be separated by whitespace.
PERMISSION: Operations in a sequence MAY be separated by whitespace in addition to the semicolon.
# 2.5 Device Descriptor
A device descriptor describes an individual PCI device on the module. The attribute of a device that is of interest is the list of functions found at that device.
RULE: A module description file SHALL include a distinct device descriptor for each device listed in an InternalBridge function descriptor’s DeviceList.
RULE: A device descriptor SHALL be named “functionNameDeviceD”, where D is the device number of the device and the DeviceList tag in a function descriptor, and functionName is the name of the function descriptor.
PERMISSION: If there is no ambiguity about which function’s DeviceList is being defined—for example, because there is only one InternalBridge function and therefore only one DeviceList in the module description file—the device descriptor name MAY omit the functionName portion of the device descriptor name. The name must include this qualifier if there would otherwise be multiple device descriptors named DeviceD, however.
RULE: Each device descriptor SHALL contain the following tags: