Understanding the Device Descriptor (DD) Directory Hierarchy in the NIFBUS/DATA Directory Primary Software: Driver Software>>NI-FBUSPrimary Software Version: 2.3.5 Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: When looking in the data directory under my nifbus installation I see several directories with cryptic names. What are these? Solution: The Foundation Fieldbus specification defines the directory structure for storing Device Descriptions (DDs) on a host machine. In the Interface Configuration Utility (where you configure the settings for your boards and ports) the DD Info button will bring up another window that specifies the base directory for your manufacturer-defined DD files. On your hard disk you will find directories with hexidecimal name under this base directory. These folders are named by manufacturer ID. You will find one folder for each different manufacturer for which you have imported DDs. For example, if you have imported the DD for the National Instruments FP-3000 device you will find a directory "4e4943". This is the National Instruments Foundation Fieldbus device manufacturer ID number (a hexadecimal number). The next layer of folders is the device type. For example, the FP-3000 has a device type ID number of 4005 (again, a hexadecimal number). Underneath this layer of directories you will find the individual DD files (.ffo and .sym) The .ffo files are the ones that you will browse for in the Interface Configuration Utility, but both are imported when you click the Import DD button. The name of the .ffo file has two parts: DEV_REV and DD_REV. These are concatenated together into one 4-digit number. So for the first device revision of the FP-3000, National Instruments shipped 0101.ffo and 0101.sym files on a disk with the hardware. Starting with Configurator software version 2.2.5, in the case that more than one revision is present (for example, 0101.ffo. and 0102.ffo), the Configurator will use the latest DD_REV for a given DEV_REV. DD files are required by the Foundation Fieldbus specification to be backwards compatible for the same DEV_REV. Note that if there is no appropriate DD for the manufacturer, device type, device revision and DD revision being returned by the device, then there is a DD mismatch. In this case NI-FBUS uses only the standard dictionary - nifb.dct and you will be unable to use any manufacturer-supplied functionality. Please note that these parameters can be read from the device's resource block. The following procedure will help you to trouble-shoot a DD_SIZE_MISMATCH_ERROR by finding out if your DD files match your device. 1. Start nifb.exe. Wait until the process has finished initializing. 2. Start the NI-FBUS Dialog Utility. 3. Right click on Open Descriptors and choose Expand All. 4. After the expansion is complete, close the Expand All window. 5. Right click on the Resource block for your device. (It should be under Open Descriptors >> Session >> Interface Name >> Device Name >> VFD Name >> Resource Block Name) Select Read Object. 6. Select the Read by Name radio button and enter MANUFAC_ID as the name. Click the Read button. Write down the hexidecimal number found in parenthesis (0xnumber). 7. Repeat step 6 for the name DEV_TYPE. 8. Repeat step 6 for the name DEV_REV. 9. Repeat step 6 for the name DD_REV. 10. Repeat steps 5-9 for each device. 11. In the Interface Configuration Utility click the DD Info button. Note the base directory specified for DDs. Close the Interface Configuration Utility. 12. Use Windows Explorer to view the contents of the base directory specified in the Interface Configuration Utility. The Fieldbus specification defines the directory hierarchy for storing DDs. There is a different directory for each device manufacturer. Under the base directory you should see a directory with the number from step 6 for the first device. 13. Under the appropriate manufacturer directory, there is a directory for each device type that you have from that manufacturer. Check to make sure that you see a directory with the number from step 7. 14. Under the appropriate device type directory, there are the individual DDs. The DD file name is a combination of the device revision (the number from step 8) and the DD revision (the number from step 9). The device revision is the first two digits, and the DD revision is the second two digits. For example, if your number from step 8 was 2 and from step 9 was 1, you should see files called 0201.ffo and 0201.sym. Also, DDs are backwards compatible. This means that instead of seeing 0201, you might see 0202. This is allowed by the Fieldbus specification. Also, having additional files in this directory is not a problem. The Configurator will use the most recent DD revision for a given device revision. If you do not have the appropriate .ffo and .sym files, you must obtain them from the device manufacturer. Be sure to properly import them by clicking on DD Info and using the Import DD button in the Interface Configuration Utility. 15. Repeat steps 12-14 for each device. Related Links: Attachments:
Report Date: 05/13/1999 Last Updated: 12/02/2004 Document ID: 1LCA68QT |
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