- 有了前面關於led的講解後,後續的相關裸奔就方便多了,當然,code就不會像led那樣簡單了~ 現在開始講解關於按鍵key的相關code
- 首先先看原理圖找到key相關的引腳,在我的tq2440板子中,有如下分佈:
key1 – INT1 – GPF1
key2 – INT4 – GPF4
key3 – INT2 – GPF2
key4 – INT0 – GPF0
從上面可以看出GPF0124除了正常的引腳輸入輸出IO功能外還有額外的作用 –> 中斷,這個我們後面會講到,到時再講解,從原理圖可以看出,引腳默認情況是高電平,當有按鍵按下時爲低電平。 接下來就是寫code了,可以將之前寫的C語言led直接copy過來改個名就可以滿足框架了,現先將code貼 出 來:
crt0.S key_loop.c Makefilecrt0.S
1 .text
2 .global _start
3 _start:
4 ldr r0, =0x53000000 @ close watch dog,or it will reboot again and again
5 ldr r1, =0x0
6 str r1, [r0]
7
8 ldr sp, =4096 @ set stack for call C function
9
10 bl main @ call C main,that's why the user code entry is main,and it will return
11 loop:
12 b loop @ call but not return
key_loop.c
1 #define GPBCON (*(volatile unsigned long *)0x56000010)
2 #define GPBDAT (*(volatile unsigned long *)0x56000014)
3 #define GPFCON (*(volatile unsigned long *)0x56000050)
4 #define GPFDAT (*(volatile unsigned long *)0x56000054)
5
6 void delay_ms(int ms)
7 {
8 int x,y;
9 for(x=ms; x>0; x--)
10 for(y=100; y>0; y--)
11 {
12 ; //do nothing
13 }
14 }
15 int main()
16 {
17 unsigned char key_value=0;
18 GPBCON |= ((1<<10) | (1<<12) | (1<<14) | (1<<16)); // set led1~4 output
19 GPFCON = 0x0; //set GPF input
20 GPBDAT = ~0x0; //set led off default
21
22 while(1)
23 {
24 key_value = GPFDAT;
25 if( 0 == (key_value & (1<<0))) //INT0 key4
26 {
27 GPBDAT = ~(1<<8); //led4 on
28 }
29
30 if( 0 == (key_value & (1<<1))) //INT1 key1
31 {
32 GPBDAT = ~(1<<5); //led1 on
33 }
34
35 if( 0 == (key_value & (1<<2))) //INT2 key3
36 {
37 GPBDAT = ~(1<<7); //led3 on
38 }
39
40 if( 0 == (key_value & (1<<4))) //INT4 key2
41 {
42 GPBDAT = ~(1<<6); //led2 on
43 }
44
45 delay_ms(20);
46 }
47
48 return 0;
49 }
Makefile
1 key.bin : crt0.S key_loop.c
2 arm-linux-gcc -c crt0.S -o crt0.o
3 arm-linux-gcc -c key_loop.c -o key_loop.o
4 arm-linux-ld -Ttext 0x0 crt0.o key_loop.o -o key.elf
5 arm-linux-objcopy -O binary -S key.elf key.bin
6 arm-linux-objdump -D -S key.elf > key.dis
7
8 clean:
9 rm -f *.o key.elf key.bin key.dis
crt0.S還是老樣子,關閉看門狗,設置好棧,最後跳轉到C的main函數,在key_loop.c中,設置key引腳爲input,我們採用的是效率很低的輪詢查詢方式,每隔一段時間就讀取值一次並做判斷哪個key按下了,然後點亮相應的led。到時將到中斷也會用這個例子,只不過不用輪詢這方式。