Design and driver transplantation of matrix keyboard circuit of Ti am335x industrial control module

The verification of this content uses yingpengfei embedded CoM-335x Core module and Evaluation Board EAC-335X, The brief introduction is as follows ：

 

 

  Preface

Compared with keys , Matrix key （ keyboard ） Use less GPIO Implement more key interfaces . following , be based on COM-335x Core module , Introduce linux The coding practice process of matrix keyboard in embedded system , Simply from the principle 、 Key value code description .

1 Principle introduction

Press the effective electric bisector of the key , It can be divided into high-level trigger and low-level trigger . In a general way , Button triggered by high level , In principle design, the uplink address is pulled down by resistance ; Low level trigger , Line address pull up . Separately shown 1-1、 chart 1-2 Shown , Pay attention to the trigger level when configuring the software .

chart 1-1 High level trigger , Row drop-down

 

chart 1-2 Low level trigger , Pull up the line

  Software level ,Linux input Subsystems provide support . Its architecture is shown in the figure 1-3, More about input Subsystem , Please refer to resources or kernel code .

chart 1-3

 2 Key configuration

Key configuration focuses on two issues , One is IO Distribute , The second is the key value .IO Distribute according to the principle , Pay attention to the effective level 、 The row is configured as input ; Key values can be obtained in two ways , Manual calculation and function call . The following two sections introduce section 1 How to configure the keys in Chapter .

2.1 Key configuration triggered by high level

, chart 1-1 The key for is 3 That's ok 2 Column , Line address drop-down .IO Configure line input 、 Column output 、 The drop-down 、 High level trigger , stay COM-335x Of dts The configuration in is as follows ：

  notes ： In the above code list , The red font is the line address IO Distribute , Black is the column address IO Distribute .

 

notes ：

① In the above code list , each GPIO The average effective electricity is high , namely ：GPIO_ACTIVE_HIGH;

② debounce-delay-ms It means time to shake , The unit is millisecond ;

③ col-scan-delay-us  Indicates the column scan interval , In microseconds .

④ linux,keymap  The value of the attribute is the key value , It is calculated that . The calculation formula is shown in the figure 2-1：

 

chart 2-1

  With “MENU” For example , Its “linux,keymap” The value of is calculated as follows ：

  from include/dt-bindings/input/linux-event-codes.h In file , find MENU The value of is 139, namely 16 It's binary 8B（ common 4 position 16 Hexadecimal number , Insufficient high-level compensation 0）, Pictured 2-2 Shown .

  chart 2-2

Sum up ,32~25 Bit is line number 、24~17 Position is listed 、 low 16 Bit is key value , convert to 16 Hexadecimal numbers are easy to read （4 position 2 A decimal number means 1 position 16 Hexadecimal number ）.0x0000008b  Express 0 That's ok 0 Column 、 The key value is 139.

2.2 Key configuration triggered by low level

chart 1-2 The key for is 6 That's ok 3 Column , Line address pull up .IO Configure line input 、 Column output 、 Pull up 、 Low level trigger , stay COM-335x Of dts The configuration in is as follows ：

notes ： In the above code list , The red font is the line address IO Distribute , Black is the column address IO Distribute .

 

 

 

notes ：

① gpio-activelow  Indicates low level trigger , If there is no such attribute , It means that the high level is valid ;

② linux,no-autorepeat  Indicates that key repetition is disabled , namely ： Long press a key , Print only once ;

③ call MATRIX_KEY Function calculates the key value , This method is better than 2.1 Section is intuitive , Please run the function as shown in the figure 2-3, The definition of key value is still from include/dt-bindings/input/linux-event-codes.h  From the file .

  chart 2-3