servoBlaster 研究筆記

他有兩個 版本

1. kernel space 版本

2.  user  space 版本

kernel 版本 compile 起來有問題....然後作者也推薦使用 user space 版本

原文如下:

There are two implementations of ServoBlaster; a kernel module based one, and a
user space daemon.  The kernel module based one is the original, but is more of
a pain to build because you need a matching kernel build.  The user space
daemon implementation is much more convenient to use and now has rather more
features than the kernel based one.  I would strongly recommend you use the
user space implementation.

進到 user folder....

編譯指令:

sudo  make

或是

sudo make install

其實兩個只差在如果你打 install... 就是開機的時候就會去load 去執行

執行指令:

$ sudo ./servod

結果如下:

Board revision:                  1
Using hardware:                PWM
Using DMA channel:              14
Idle timeout:             Disabled
Number of servos:                8
Servo cycle time:            20000us
Pulse increment step size:      10us
Minimum width value:            50 (500us)
Maximum width value:           250 (2500us)
Output levels:              Normal

Using P1 pins:               7,11,12,13,15,16,18,22

Servo mapping:
     0 on P1-7           GPIO-4
     1 on P1-11          GPIO-17
     2 on P1-12          GPIO-18
     3 on P1-13          GPIO-27
     4 on P1-15          GPIO-22
     5 on P1-16          GPIO-23
     6 on P1-18          GPIO-24
     7 on P1-22          GPIO-25

它總共有八個PWM 輸出....

If you want
to stop servod, the easiest way is to run:

$ sudo killall servod

The
default option is the equivalent of specifying

   --p1pins=7,11,12,13,15,16,18,22

可以修改的地方

Q1 :  如果只要四個輸出...要怎改?

 A1 :
        修改  servod.c

      把static char *default_p1_pins = "7,11,12,13,15,16,18,22";

改成static char *default_p1_pins = "7,11,12,13";

就可以了

Q2 : 如何改pulse width 的最小值（1000us）...最大值(2000us)

A2 :   
    
     #define DEFAULT_SERVO_MIN_US  500
    #define DEFAULT_SERVO_MAX_US  2500

     改成

     單位是 1 us

    #define DEFAULT_SERVO_MIN_US  1000

    #define DEFAULT_SERVO_MAX_US  2000

Q3 :   如何更改  cycle time,  改成 490Hz -> (1000000/490 = 2040):

         #define DEFAULT_CYCLE_TIME_US   20000

         改成#define DEFAULT_CYCLE_TIME_US   2040

     

Q4 :   如何更改  step_size ,  從 10us 改成 2us...

        

          #define DEFAULT_STEP_TIME_US    10

         改成#define DEFAULT_STEP_TIME_US    2

      

    

Q5 :   如何動態更改pulse寬度

        指定us 的方式

       echo P1-7=1500us > /dev/servoblaster

指定 step 的方式   

echo P1-7=150 > /dev/servoblaster # Using P1 pin number rather

Reference : https://github.com/richardghirst/PiBits/tree/master/ServoBlaster