Luoda Development -- the context of sidetone configuration

Chip model ：AB1565

Function module ：Side Tone

Function description ：Side Tone It is used to guide the external sound of the earphone into the ear , So that people can hear the natural sound outside the earphone , The best case is to hear the external sound as if there were no headphones .

---

chart 1 chart 2 by Side Tone Function call relationship of unit , It will be configured during the process Side Tone Of Filter And the gain of transparency . Jizhong DTM() by FreeRTOS A task of , The task will run continuously after the software is started , And maintain a named dtm_queue Local queues for , All and Side Tone Relevant operation commands will be sent to the queue first , Then by the Task To extract commands from the queue and execute them accordingly , Its working logic is shown in the figure 2 Shown .

chart 1：Side Tone Related function call relationship

 

chart 2：SideTone Related message processing tasks

 

• Filter

The filtering coefficient is used to do EQ Handle , For example, the restoration of timbre , Noise elimination 、 Inhibit or enhance . These systems , It is preset in the code in advance , Of course, these parameters can also be dynamically modified by programming , For instance from BL Import and store in the specified location ,SDK in , The position of this coefficient is shown in the figure 1 Sum graph 3 Shown , Eventually these coefficients are written into registers “AFE_SIDETONE_CON0” in .

chart 3：SDK The built-in Side Tone Filter coefficient problem

 

So how is the writing of this coefficient stored ？ Let me see the chip again Reference Manual, It's about AFE_SIDETONE_CON0 The definition of registers , Pictured 4 Shown , The red box indicates that the control coefficient is written RAM Correlation bit of .

bit[20:16] Is the address of the coefficient , District 5 individual bit position , Therefore, we can know that the coefficient can only be 2^5=32 individual （ Of course, it can be less than 32 individual ）.

and bit[15:0] Is the coefficient value （ The format is Q1.15）, Therefore, when writing, you need to perform the same number of write operations according to the number of coefficients .

chart 4：AFE_SIDETONE_CON0 Register definition

 

• gain

It is to adjust the intensity of external sound penetrating into the ear , Ideally, the gain should be dynamic and have an upper threshold , It has the function of amplifying small sounds , Suppress loud sounds , So as to form a hearing protection effect ;

Whether it's filter still gain, Finally, the formation factors are written into AB1656 The corresponding register , namely AFE_SIDETONE The following registers .

that gain How to write the chip ？ Pictured 1 Shown , among ” dsp_sidetone_set_volume()” And “dsp_sidetone_start_volume_set()” Function is configuration sidetone The relevant interface function of the gain , Pictured 5 Shown .

Plotting 5：SideTone Interface function question

  From the picture 5 You can find , The gain value is finally written to the register AFE_SIDETONE_GAIN in , So how is this register defined ？ We look at the picture 6, It can be found that there are two about gain ：Positive Gain and SideToneGain（ The difference between the two has not been studied yet ）.

Headline figure 6：SideTone Gain configuration register