當我們閱讀『技術文件』時，為什麼老覺得咬文嚼字，難以下咽的呢？這是因為『技術文件』之『術語』定義，必要的『精確性』 ── 精準且正確 ── 使然。比方說， CPU 的『存取單位』是一個『模糊』的名詞。因為『資料匯流排』 data bus 有多少『位元』的寬度，決定了那個 CPU 資料『存取單位』的大小。更不要說還有那『位元組』 byte 排序問題，因此不同種類的 CPU ，就有了『位元組序』 Endianness 的『大‧小』之區分。再加上許多『技術文件』通常用於整個『事物族系』，散布於『技術文件』的『不同部份』 ，很容易導致了『不知全盤』就『難知其一』的現象。舉例來講，什麼是『輸入事件』 input event ？假使我們查詢『 input_event 』名稱在 Kernel 4.1.X 中使用之『交互參考』，恐怕會暈頭轉向的吧！如果對『輸入裝置』這個子系統多些了解之後，也許從下面的資料『樣板結構』，就能知道梗概的了︰

Linux/include/uapi/linux/input.h
20 /*
21 * The event structure itself
22 */
23
24 struct input_event {
25 struct timeval time;
26 __u16 type;
27 __u16 code;
28 __s32 value;
29 };
30

這裡『__u16』和『__s32』都是指『位元』之大小，假使想更清楚知道這個『資料結構』大小及意義，還得先知道『__kernel_time_t』與『__kernel_suseconds_t』之大小及意義！！

Linux/include/uapi/linux/time.h
14
15 struct timeval {
16 __kernel_time_t tv_sec; /* seconds */
17 __kernel_suseconds_t tv_usec; /* microseconds */
18 };
19

這也就是一般 kernel 裝置『驅動程式』學習的為難處。因此若想『學習』 PiTFT 的『觸控輸入』，用

pi@raspberrypi ~  evtest /dev/input/touchscreen 
Input driver version is 1.0.1
Input device ID: bus 0x18 vendor 0x0 product 0x0 version 0x0
Input device name: "stmpe-ts"
Supported events:
  Event type 0 (EV_SYN)
  Event type 1 (EV_KEY)
    Event code 330 (BTN_TOUCH)
  Event type 3 (EV_ABS)
    Event code 0 (ABS_X)
      Value   1851
      Min        0
      Max     4095
    Event code 1 (ABS_Y)
      Value   2714
      Min        0
      Max     4095
    Event code 24 (ABS_PRESSURE)
      Value      0
      Min        0
      Max      255
Properties:
Testing ... (interrupt to exit)
Event: time 1439617362.428940, type 3 (EV_ABS), code 0 (ABS_X), value 2413
Event: time 1439617362.428940, type 3 (EV_ABS), code 1 (ABS_Y), value 2222
Event: time 1439617362.428940, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 93
Event: time 1439617362.428940, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 1
Event: time 1439617362.428940, -------------- SYN_REPORT ------------
Event: time 1439617362.435368, type 3 (EV_ABS), code 0 (ABS_X), value 2482
Event: time 1439617362.435368, type 3 (EV_ABS), code 1 (ABS_Y), value 2238
Event: time 1439617362.435368, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 100
Event: time 1439617362.435368, -------------- SYN_REPORT ------------
Event: time 1439617362.441796, type 3 (EV_ABS), code 0 (ABS_X), value 2484
Event: time 1439617362.441796, type 3 (EV_ABS), code 1 (ABS_Y), value 2249
Event: time 1439617362.441796, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 97
Event: time 1439617362.441796, -------------- SYN_REPORT ------------
Event: time 1439617362.448270, type 3 (EV_ABS), code 0 (ABS_X), value 2550
Event: time 1439617362.448270, type 3 (EV_ABS), code 1 (ABS_Y), value 2256
Event: time 1439617362.448270, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 98
Event: time 1439617362.448270, -------------- SYN_REPORT ------------
Event: time 1439617362.454676, type 3 (EV_ABS), code 0 (ABS_X), value 2561
Event: time 1439617362.454676, type 3 (EV_ABS), code 1 (ABS_Y), value 2258
Event: time 1439617362.454676, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 96
Event: time 1439617362.454676, -------------- SYN_REPORT ------------
Event: time 1439617362.461091, type 3 (EV_ABS), code 0 (ABS_X), value 2555
Event: time 1439617362.461091, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 97
Event: time 1439617362.461091, -------------- SYN_REPORT ------------
Event: time 1439617362.483105, type 3 (EV_ABS), code 0 (ABS_X), value 2536
Event: time 1439617362.483105, type 3 (EV_ABS), code 1 (ABS_Y), value 2259
Event: time 1439617362.483105, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 101
Event: time 1439617362.483105, -------------- SYN_REPORT ------------
Event: time 1439617362.554620, type 3 (EV_ABS), code 24 (ABS_PRESSURE), value 0
Event: time 1439617362.554620, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 0
Event: time 1439617362.554620, -------------- SYN_REPORT ------------

 

看似易讀，總『留有疑惑』，終究有賴於『整體了解』的耶？？此正是研讀『高階程式庫』，更需要小心之處︰

events

This module provides the InputEvent class, which closely resembles the input_event struct defined in linux/input.h:

struct input_event {
    struct timeval time;
    __u16 type;
    __u16 code;
    __s32 value;
};

This module also defines several InputEvent sub-classes that know more about the different types of events (key, abs, rel etc). The event_factory dictionary maps event types to these classes.

Assuming you use the evdev.util.categorize() function to categorize events according to their type, adding or replacing a class for a specific event type becomes a matter of modifying event_factory.

All classes in this module have reasonable str() and repr() methods:

>>> print(event)
event at 1337197425.477827, code 04, type 04, val 458792
>>> print(repr(event))
InputEvent(1337197425L, 477827L, 4, 4, 458792L)

>>> print(key_event)
key event at 1337197425.477835, 28 (KEY_ENTER), up
>>> print(repr(key_event))
KeyEvent(InputEvent(1337197425L, 477835L, 1, 28, 0L))

 

，一旦『望文生義』常是『囫圇吞棗』之結果？？所以請對眾多之『術語』務必清楚明白，這才是應用真實的基礎也！！

能夠嘗試『解讀』他人來源碼，或正是『寫程式』之基本功乎！？

pi@raspberrypi ~ $ python3
Python 3.2.3 (default, Mar  1 2013, 11:53:50) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from evdev import InputDevice, list_devices, categorize, ecodes
>>> devices = [InputDevice(fn) for fn in list_devices()]
>>> for dev in devices:
...     print(dev.fn, dev.name, dev.phys)
... 
/dev/input/event2 Gwell HicHan RF-Dongle usb-3f980000.usb-1.2/input1
/dev/input/event1 Gwell HicHan RF-Dongle usb-3f980000.usb-1.2/input0
/dev/input/event0 stmpe-ts stmpe-ts/input0
>>> 
>>> dev = InputDevice('/dev/input/event0')
>>> print(dev)
device /dev/input/event0, name "stmpe-ts", phys "stmpe-ts/input0"
>>> 
>>> dev.capabilities()
{0: [0, 1, 3], 1: [330], 3: [(0, AbsInfo(value=2212, min=0, max=4095, fuzz=0, flat=0, resolution=0)), (1, AbsInfo(value=2904, min=0, max=4095, fuzz=0, flat=0, resolution=0)), (24, AbsInfo(value=0, min=0, max=255, fuzz=0, flat=0, resolution=0))]}
>>> 
>>> dev.capabilities(verbose=True)
{('EV_KEY', 1): [('BTN_TOUCH', 330)], ('EV_ABS', 3): [(('ABS_X', 0), AbsInfo(value=2212, min=0, max=4095, fuzz=0, flat=0, resolution=0)), (('ABS_Y', 1), AbsInfo(value=2904, min=0, max=4095, fuzz=0, flat=0, resolution=0)), (('ABS_PRESSURE', 24), AbsInfo(value=0, min=0, max=255, fuzz=0, flat=0, resolution=0))], ('EV_SYN', 0): [('SYN_REPORT', 0), ('SYN_CONFIG', 1), ('SYN_DROPPED', 3)]}
>>> 
>>> for event in dev.read_loop():
...     if event.type == ecodes.EV_ABS:
...         print(categorize(event))
... 
absolute axis event at 1439627454.210421, ABS_X 
absolute axis event at 1439627454.210421, ABS_Y 
absolute axis event at 1439627454.210421, ABS_PRESSURE 
absolute axis event at 1439627454.241907, ABS_X 
absolute axis event at 1439627454.241907, ABS_Y 
absolute axis event at 1439627454.241907, ABS_PRESSURE 
absolute axis event at 1439627454.257593, ABS_X 
absolute axis event at 1439627454.257593, ABS_Y 
absolute axis event at 1439627454.257593, ABS_PRESSURE 
absolute axis event at 1439627454.264023, ABS_X 
absolute axis event at 1439627454.264023, ABS_Y 
absolute axis event at 1439627454.264023, ABS_PRESSURE 
absolute axis event at 1439627454.270441, ABS_X 
absolute axis event at 1439627454.270441, ABS_Y 
absolute axis event at 1439627454.270441, ABS_PRESSURE 
absolute axis event at 1439627454.276901, ABS_X 
absolute axis event at 1439627454.276901, ABS_Y 
absolute axis event at 1439627454.276901, ABS_PRESSURE 
absolute axis event at 1439627454.380102, ABS_PRESSURE