Keyword Detection Driver Implementation and User Guide

Keyword Detection

Keyword Detection (KD), also known as Voice Activation or Sound Trigger, is a feature that triggers a speech recognition engine when a predefined keyphrase (keyword) is successfully detected. Offloading the keyphrase detection algorithm to the embedded processing environment (i.e. dedicated DSP) reduces system power consumption while listening for an utterance.

To learn how to integrate a 3rd-party detection algorithm into the SOF firmware, refer to Keyword Detection integration.

Keyword Detection pipelines

# PCM  <-----(pipe 8)--------- host <---------------- KPB <------- Volume <--- DMIC (dmic16k)
#  |                                                   |
#  |                                                   |
#  |                                                   |
# Detector Sink <---Detector(pipe 9) <--- selector <---+

We use DAPM events to trigger the detect pipeline (pipe 9). Here, the Detector Sink is a virtual DAPM widget (visible to the driver, but not to the FW). It is used to send pipeline control IPCs (hw_params, trigger start/stop, hw_free) to the firmware. These control IPCs are sent to the firmware in a sequence like this (1->2(2.1->2.2)->3->4->5->6(6.1->6.2)):

Table 3 DAPM events and stream control sequence


Pipe 8

Detector Sink event

Pipe 9





trigger start



trigger stop







Kcontrols for Keyword Detection

The KWD detection topology contains several kcontrols mainly belonging to the following types:

PGA kcontrol

These are associated with the volume components and are used to adjust the volume after the samples are captured by DMIC.

numid=12,iface=MIXER,name='PGA8.0 8 KWD Capture Volume'

Bytes kcontrols

KPB, Selector, and Detector are all treated as processing type components in the SOF driver. Each of these components have an associated byte type kcontrol and are configured using the default values from topology as follows:

KPB kcontrol

The kcontrol for the KPB configuration is (amixer controls | grep “KPB”):

numid=13,iface=MIXER,name='KPBM8.0 KPB'

The initial value of it is in the KPB_priv section of sof/tools/topology/sof/pipe-kfbm-capture.m4 (the first 32 Bytes are the abi header); it is aligned with the definition of struct sof_kpb_config in sof/include/user/kpb.h.

Selector kcontrol

The kcontrol for the Selector configuration is (amixer controls | grep “SELECTOR”):

numid=16,iface=MIXER,name='SELECTOR9.0 SELECTOR'

The initial value of it is in the SELECTOR_priv section of sof/tools/topology/sof/pipe-detect.m4 (the first 32 Bytes are the abi header); it is aligned with the definition of struct sof_sel_config in sof/include/user/selector.h.

Detector kcontrol for component configuration

The kcontrol for the Detector configuration is (amixer controls | grep “Detector Config”):

numid=14,iface=MIXER,name='DETECT9.0 Detector Config'

The initial value of it is in the DETECTOR_priv section of sof/tools/topology/m4/detect_test_coef.m4 (the first 32 Bytes are the abi header); it is aligned with the definition of struct sof_detect_test_config in sof/include/user/detect_test.h.

Detector kcontrol for algorithm data

The kcontrol for the detector algorithm configuration is (amixer controls | grep “Hotword Model”):

numid=15,iface=MIXER,name='DETECT9.0 Hotword Model'

This is vendor-specific; by default, it is initialized to 64 Bytes 0s only.

The sof-ctl tool

For all TLV Bytes kcontrols, after the pipeline/PCM is created, we can use the SOF tool named sof-ctl to configure/update with the new blob.

The source is located in sof/tools/ctl/ctl.c. Run ./scripts/ in the sof folder to build and generate it.

To set:

#./sof-ctl -Dhw:0 -c name='DETECT9.0 Hotword Model' -br -s en_us_data_memory.mmap -t 1

To read it back:

#./sof-ctl -Dhw:0 -c name='DETECT9.0 Hotword Model' -br

Run the Keyword Detection pipeline

After the Detector blob is configured, we run aplay/arecord to verify the KWD on our side. Run it in mmap -M non-blocking -N mode, as shown in the example below:

#arecord -Dhw:0,8 -M -N -c 2 -f S16_LE -r 16000 --buffer-size=68000 tmp.wav -vvv

The supported formats of the PCM are 16KHz s16_le/s24_le/s32_le 2 channels.


The waking up and the host system resuming may take up to 1~2 seconds. To make sure the captured keyword data is not overwritten by the subsequent realtime data, the host buffer-size must be at least 67200 frames (4.2 Seconds); smaller values will be rejected by the firmware and will fail at the hw_param stage.

Run the Keyword Detection feature at S0ix status

In one terminal, run:

#arecord -Dhw:0,8 -M -N -c 2 -f S16_LE -r 16000 --buffer-size=64000 tmp.wav -vvv

In another terminal, run:

#echo freeze > /sys/power/state

The Keyword Detection feature is activated at S0Ix. Say the keyword to trigger the Keyword detected; the system wakes up and the keyword and command data are captured.