BEAGLEBK: Rotary encoder driver

Hi,

Does anyone know about the answers? Any suggestions will be appreciated.

Thank you!

Hi Ron,

Thank you. This certainly helps.

After some investigation, I wanted to get a few things clarified:

1. I am not quite clear about the device tree binding format.
Suppose I have GPIO0_22 and GPIO0_23 connected to Y axis ENC_A and ENC_B signals respectively. The maximum value of the Y axis encoder counter value is 2^20. Is the following device tree correct? Please correct me if this is not.

gpio-decoder0 {
        compatible = "gpio-decoder";
        gpios = <&gpio0 22 GPIO_ACTIVE_HIGH>,
                      <&gpio0 23 GPIO_ACTIVE_HIGH>;
                       linux,axis = <1>; /* ABS_Y */
                       decoder-max-value = <1048576>;
};

 
2. To read the encoder value from a userspace C application, I suppose we can just call read():
struct input_event event;
fd = open("/dev/input/eventX", O_RDONLY);
...
read(fd, &event, sizeof(event));
printf("Y value: %d\n", event.value);

I am not sure if my understanding is correct or not. But it looks like for this driver the user space application will get the states of two GPIOs when they change, not the values of encoder count, correct?

This means for a quadrature encoder, if there are 1000 steps per seconds for 3 motors, there will be 1000 * 4 * 3 = 12000 state changes. If the user space application miss one of them, the encoder count will be incorrect?

In this case, will this driver also work and work better?

https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/drivers/input/misc/rotary_encoder.c?h=linux-4.19.y

Please explain if my understanding is incorrect.

3. How do we set the encoder value (for example, set the value to 0)?

Thank you for your help.