一,前言
今天玩一下US100超聲波傳感器。5年前玩尋路小車的時候用過,已經忘記了。先看了下它的原理,除了支持gpio還支持uart的。給它輸入0x55命令可以獲取2個字節的距離mm信息。那麼我就用下串口子系統。基於console的其實一直在用,但是我都沒了解過tty的框架。正好網上了解下,資料比較多,我就不多說。配置完設置樹,使用8250底層uart驅動及tty驅動,所以驅動不用自己寫,配置完設備樹,寫了read/write APP就能用了。工程已上傳我的gitee工程13。
二,設備樹修改
a.先用PC串口調試助手使用了下US100。驗證器件正常。GND我就連接了一根。
b.看了下datasheet及原理圖,決定使用UART1。
am335x-bone-common.dtsi修改下
uart1_pins: pinmux_uart1_pins {
pinctrl-single,pins = <
AM33XX_PADCONF(AM335X_PIN_UART1_RXD, PIN_INPUT_PULLUP, MUX_MODE0)
AM33XX_PADCONF(AM335X_PIN_UART1_TXD, PIN_OUTPUT_PULLDOWN, MUX_MODE0)
>;
};
&uart1 {
pinctrl-names = "default";
pinctrl-0 = <&uart1_pins>;
status = "okay";
};
三,遇到的問題
1. 到底註冊到哪個設備了,那麼多tty。
log信息可以看出註冊到了ttyS1
[ 1.013776] Serial: 8250/16550 driver, 6 ports, IRQ sharing enabled
[ 1.019091] 44e09000.serial: ttyS0 at MMIO 0x44e09000 (irq = 29, base_baud = 3000000) is a 8250
[ 1.814064] printk: console [ttyS0] enabled
[ 1.820211] 48022000.serial: ttyS1 at MMIO 0x48022000 (irq = 35, base_baud = 3000000) is a 8250
設備描述中也可以看到更詳細的內容。
# pwd
/sys/bus/platform/drivers/omap8250/48022000.serial
# ls -al
total 0
drwxr-xr-x 5 root root 0 Jan 1 00:02 .
drwxr-xr-x 4 root root 0 Jan 1 00:02 ..
lrwxrwxrwx 1 root root 0 Jan 1 00:02 driver -> ../../../../../../../bus/platform/drivers/omap8250
-rw-r--r-- 1 root root 4096 Jan 1 00:02 driver_override
-r--r--r-- 1 root root 4096 Jan 1 00:02 modalias
lrwxrwxrwx 1 root root 0 Jan 1 00:02 of_node -> ../../../../../../../firmware/devicetree/base/ocp/interconnect@48000000/segment@0/target-module@22000/serial@0
drwxr-xr-x 2 root root 0 Jan 1 00:02 power
lrwxrwxrwx 1 root root 0 Jan 1 00:02 subsystem -> ../../../../../../../bus/platform
drwxr-xr-x 3 root root 0 Jan 1 00:02 tty
-rw-r--r-- 1 root root 4096 Jan 1 00:02 uevent
drwxr-xr-x 3 root root 0 Jan 1 00:02 wakeup
# cd tty
# ls
ttyS1
2. write一直阻塞。
我的app是先write 0x55,然後read 2字節,結果write就阻塞了。懷疑線反了,反接後依然write 阻塞。於是用示波器,看了下波形幅度值不到5。所以將usb上電改成了電源上電。問題解決。示波器發送0x55截圖如下,
另外,我用echo -e -n "\x55" > /dev/ttyS1截圖也是一樣的。並且由於發送成功,所以我截取rx腳,接收也成功。接收2字節如下圖
3. read一直阻塞
示波器都已經顯示read有正常的波形,但是read一直被阻塞。我懷疑杜邦線斷了,用萬用表測量線正常。難道是沒有進入中斷。我之前看框架的時候ftrace也跟蹤過,但是ftrace內容太多了,因爲uart0也是用8250,所以我區分不了。那麼從/proc/interrupts來查看中斷。如下可以看出35號中斷一開始是沒有的,運行了us程序後,35號中斷出現。最後我只能看源碼,當然最快的速度是網上找下框架資料,比如接收中斷是哪個函數,然後又會調用哪裏。接着找到了線索,他描述的接收中斷居然是從console輸入作爲接收中斷的,然後echo回顯到console。那麼我立即想到一個問題,我不用console的,是否就不能喚醒read中。所以是否有些設置bypass console。本來想看了document的幫助,因爲我覺得linux的串口驅動不會有bug的,先網上搜索下,立即得到答案。原來需要設置raw模塊的串口通信。在raw模式下最後運行app,獲取結果正確。
# cat /proc/interrupts
CPU0
16: 618 INTC 68 Level gp_timer
18: 0 INTC 3 Level arm-pmu
19: 8 INTC 12 Level 49000000.edma_ccint
21: 0 INTC 14 Level 49000000.edma_ccerrint
28: 0 INTC 96 Level 44e07000.gpio
29: 108 INTC 72 Level 44e09000.serial
30: 146 INTC 70 Level 44e0b000.i2c
43: 0 INTC 98 Level 4804c000.gpio
44: 37 INTC 64 Level mmc0
46: 0 INTC 30 Level 4819c000.i2c
47: 0 INTC 32 Level 481ac000.gpio
48: 0 INTC 62 Level 481ae000.gpio
49: 47 INTC 28 Level mmc1
53: 1191 INTC 41 Level 4a100000.ethernet
54: 689 INTC 42 Level 4a100000.ethernet
57: 0 44e07000.gpio 6 Edge 48060000.mmc cd
58: 0 INTC 7 Level tps65217-irq
IPI0: 0 CPU wakeup interrupts
IPI1: 0 Timer broadcast interrupts
IPI2: 0 Rescheduling interrupts
IPI3: 0 Function call interrupts
IPI4: 0 CPU stop interrupts
IPI5: 0 IRQ work interrupts
IPI6: 0 completion interrupts
Err: 0
# cd /usr/study/
#
# ./us &
# ok
# cat /proc/interrupts
CPU0
16: 1012 INTC 68 Level gp_timer
18: 0 INTC 3 Level arm-pmu
19: 8 INTC 12 Level 49000000.edma_ccint
21: 0 INTC 14 Level 49000000.edma_ccerrint
28: 0 INTC 96 Level 44e07000.gpio
29: 247 INTC 72 Level 44e09000.serial
30: 146 INTC 70 Level 44e0b000.i2c
35: 0 INTC 73 Level 48022000.serial
43: 0 INTC 98 Level 4804c000.gpio
44: 37 INTC 64 Level mmc0
46: 0 INTC 30 Level 4819c000.i2c
47: 0 INTC 32 Level 481ac000.gpio
48: 0 INTC 62 Level 481ae000.gpio
49: 47 INTC 28 Level mmc1
53: 1373 INTC 41 Level 4a100000.ethernet
54: 764 INTC 42 Level 4a100000.ethernet
57: 0 44e07000.gpio 6 Edge 48060000.mmc cd
58: 0 INTC 7 Level tps65217-irq
IPI0: 0 CPU wakeup interrupts
IPI1: 0 Timer broadcast interrupts
IPI2: 0 Rescheduling interrupts
IPI3: 0 Function call interrupts
IPI4: 0 CPU stop interrupts
IPI5: 0 IRQ work interrupts
IPI6: 0 completion interrupts
Err: 0
四 測試結果正確
不同的障礙物距離,顯示的結果不同。
# stty -F /dev/ttyS1 9600 raw
# ./us
ok
write 0x55
distance is 91
write 0x55
distance is 45
write 0x55
distance is 198
write 0x55
distance is 120
write 0x55
distance is 1579
五,參考網址
a.http://blog.chinaunix.net/uid-27717694-id-3493611.html
b.https://blog.csdn.net/shipinsky/article/details/82177143
c.https://blog.csdn.net/lhl_blog/article/details/82254056