As with host mode testing, it is crucial to begin the test procedure with all cabling and devices disconnected, including the USB device that is receiving the test packet command. Using the steps shown in the following test procedure correctly ensures that proper enumeration and activation of high-speed conditioning occurs:

1. Connect TUSB21XX input to host via relay/switching board.
2. Connect relay board to oscilloscope.
3. Toggle RSTN (reset) on TUSB21XX.
4. Connect device to TUSB21XX output.
5. Set relay board to "init" position.
6. Send high-speed test packet command via xHCI Electrical Test Tool (Figure 3-2).
7. Set relay board to "test" position.

Initially, both ENA_HS and CD status flags are low. Immediately after device connection (Step 4), DP/DM pull-up resistors are detected and the CD status flag switches high (Figure 3-3). Shortly later, after device enumeration, ENA_HS switches high (Figure 3-4). If this does not occur, ensure that the device being used is USB 2.0 high-speed compatible and that the host is able to enumerate the device (the host controller is not mounted by any software).

After sending the test packet command in software (Step 6) and setting the relay board to the "test" position (Step 7), test packets immediately begin to appear on the oscilloscope input (Figure 3-5). These will continue until the device is disconnected, at which point both CD and ENA_HS fall low (Figure 3-6).