Introduction
There are times when it is convenient to use two protocol analyzers at two different points in a system and be able to cross reference the traces. One example would be a Serial ATA (SATA) drive attached to a USB interface. You would need one analyzer to monitor and capture traffic from the SATA drive as well as a second analyzer to monitor the USB side. Another example might be a USB Bluetooth Dongle, where a USB analyzer would be used to monitor the USB side of the Dongle and a Bluetooth analyzer can be used to monitor the RF side. Both of these scenarios can benefit from external cross-triggering setups.
There are two choices for the method of synchronization between the two different protocol analyzers. The first option is to use a cable with BNC connectors on either end, and connect this cable to the BNC connectors on the rear of the two analyzers. The second option supported by all analysers except the PCMCIA based mobile units is to use the breakout board. The Breakout board has a number of input and output pins on it which can be used in a number of ways. In the simplest form the trigger out on one breakout board is wired to the trigger in on another. You might for example connect two SCSI analysers to a bus and set one to run in recirculate mode the other to run in normal mode. The normal mode analyser would then be set to set its trig out when a certain protocol sequence is observed but otherwise is set to discard data. The trig in on the recirculate analyser is then used to capture the full bus traffic based on the protocol decode trig out of the first analyser. Another breakout configuration may use two (or more) analysers to trigger a third. In this scenario the bread-boarding section might be used to add additional logic to AND or OR or similar if required. In the case where multiple inputs are available ot the breakout board (such as on the USB Chief) these can be logically combined in the firmware (be careful to tie un-used inputs to an appropriate logic level for the combination used).
Using BNC Connectors to Cross-trigger
Example 1: Trace a USB High-Speed device to a Serial ATA data path using the CATC Advisor™, USB protocol analyzer, and the CATC SATracer™, Serial ATA protocol analyzer.
Step1: Connect the analyzers to their respective devices for analysis.
Step 2: Connect the BNC Trig In on the rear of the Advisor analyzer to the BNC Trig Out of the SATracer analyzer:
Step 3: Set the trigger options of the two systems. In general, it is best to use Event triggers to provide the closest correlation between the two systems.
For the Advisor, you would set the Event triggers as shown in this screen shot:
For the SATracer, you need to set a trigger for the first read of sector LBA#0
Next for the SATracer, on the actions tab, you need to enable the general purpose output by clicking on the blue circle in the top left of the cmd cell.
Now, when the USB host sends the first command that causes the SATA drive to read LBA0, it will trigger both the USB analyzer and the SATA analyzer.
With strategic use of the Pre/Post buffer position and buffer sizes, the USB command and the response data can be captured in both systems. A red trigger marker will be placed in both the USB and SATA traces to indicate the synchronized trigger point.
Using Breakout Boards to Cross-trigger
Example 2: Using the CATC Merlin™, a Bluetooth protocol analyzer, and the CATC Chief™, a USB protocol analyzer, to trigger when a specific USB Bluetooth HCI command is sent to a Bluetooth dongle.
Step1: Connect the analyzers to their respective devices for analysis.
Step2: Now we need to connect the breakout boards triggers together, the trigger out on the USB Chief Breakout board and GND should be connected to the trigger In and GND on the Merlin Breakout board
Again in the trigger options for each analyser we need to set one to receive an external trigger and the other to generate one.
For Example in the USB Chief
Set Chief to trigger on HCI create Connection (0x0405) command, then click the small blue circle in the data pattern on the action tab to enable trigger output.
At the same time in the Merlin SW
Enable the trigger event for the External inputs.
Both units can now put into record mode and the device activity can be started. When the USB system sees the event it will cause a trigger on the input of the Merlin unit effectively synchronising the two devices relative to the trigger point.
Conclusion
Similar techniques can be used to trigger external devices like Oscilloscopes and Spectrum analysers if desired. We will run a second article next month describing how to use the external triggering in conjunction with the traffic generator to perform Compliance EYE tests.
Step 3: Set the trigger options of the two systems. One analyzer needs to be set to receive an external trigger and the other analyzer set to generate the trigger.
For the Chief, you would first set the USB analyzer to trigger on HCI create Connection (0x0405) command, then click the small blue circle in the data pattern on the action tab to enable trigger output.
At the same time, in the Merlin software, enable the trigger event for the External inputs.
Similar techniques can be used to trigger external devices like Oscilloscopes and Spectrum analysers if desired. We will run a second Application Note next month describing how to use the external triggering in conjunction with the traffic generator to perform Compliance EYE tests.
