pounder: add serial-only tests

src/hw/stabilizer_pounder.md

@@ -146,9 +146,32 @@ SMA connectors should line up with the ones from Stabilizer; no pins should be v
 
 ## Testing the Pounder
 
+### With serial only
+
+You need to have the Stabilizer powered on and connected through USB. Ethernet is not necessary.
+
+Input the following sequence of commands into the shell, assuming Stabilizer serial interface is visible at /dev/ttyACM0:
+```
+stty 115200 -F /dev/ttyACM0
+echo 'set /dual_iir/pounder/out_channel/0/dds/frequency 20e6' > /dev/ttyACM0
+echo 'set /dual_iir/pounder/out_channel/0/dds/amplitude 1' > /dev/ttyACM0
+echo 'set /dual_iir/pounder/out_channel/0/attenuation 16' > /dev/ttyACM0
+echo 'set /dual_iir/pounder/out_channel/1/dds/frequency 30e6' > /dev/ttyACM0
+echo 'set /dual_iir/pounder/out_channel/1/dds/amplitude 1' > /dev/ttyACM0
+echo 'set /dual_iir/pounder/out_channel/1/attenuation 16' > /dev/ttyACM0
+```
+
+You can copy them all and input at once.
+
+Observe a sine wave with frequency of 20MHz on channel 0 output, and 30MHz on channel 1 output.
+
+### With MQTT (slower)
+
+For this method, you need to set up MQTT and have the Stabilizer connected with Ethernet.
+
 1. Set up the MQTT as described above.
 2. Using Mosquitto and MQTT Explorer, set the pounder ``out_channel`` parameters:
-* Frequency: 10e6 (10MHz)
+* Frequency: 20e6 (20MHz)
 * Amplitude: 1.0
    ![Pounder MQTT settings](../img/pounder_mqtt.png)
 3. Repeat the procedure for the other channel.