dts: add start Tx first method to testpmd shell

Add start tx_first method to testpmd shell, which sends
a specified number of burst packets prior to starting
packet forwarding.

Signed-off-by: Dean Marx <[email protected]>
Reviewed-by: Luca Vizzarro <[email protected]>
Reviewed-by: Patrick Robb <[email protected]>

Author: dmarxIOL

dts/api/testpmd/__init__.py

@@ -214,6 +214,27 @@ def start(self, verify: bool = True) -> None:
                 self._logger.debug(f"Failed to start packet forwarding: \n{start_cmd_output}")
                 raise InteractiveCommandExecutionError("Testpmd failed to start packet forwarding.")
 
+    @_requires_started_ports
+    def start_tx_first(self, burst_num: int, verify: bool = True) -> None:
+        """Start packet forwarding after sending specified number of bursts of packets.
+
+        Args:
+            burst_num: Number of packets to send before stopping transmission.
+            verify: If :data:`True` , a second start command will be sent in an attempt to verify
+                packet forwarding started as expected.
+
+        Raises:
+            InteractiveCommandExecutionError: If `verify` is :data:`True` and forwarding fails to
+                start or ports fail to come up.
+        """
+        self.send_command(f"start tx_first {burst_num if burst_num is not None else ""}")
+        if verify:
+            # If forwarding was already started, sending "start" again should tell us
+            start_cmd_output = self.send_command("start")
+            if "Packet forwarding already started" not in start_cmd_output:
+                self._logger.debug(f"Failed to start packet forwarding: \n{start_cmd_output}")
+                raise InteractiveCommandExecutionError("Testpmd failed to start packet forwarding.")
+
     def stop(self, verify: bool = True) -> str:
         """Stop packet forwarding.