# 實驗: GPIO 的存取 ## GPIO 的硬體需求 GPIO 和硬體相關，因此，若是要能夠在 OpenWRT 上存取 GPIO，就需要硬體與韌體的支援。對於我們所使用的平台 (GL-AR300M 和 GL-AR750S) 來說，都支援 GPIO ，因此我們在這兩個平台上進行測試。以下是 GL-AR300M 和 GL-AR750S 的對應表。 | | GL-AR300M | GL-AR750S | | ---- | --------- | --------- | | I2C | GPIO16 | GPIO5 | | I2C | GPIO17 | GPIO21 | | UART | GPIO9 | GPIO18 | | UART | GPIO10 | GPIO22 | ## GPIO 的操作指令 以下指令以操作 GL-AR300M 的 GPIO16 為例。 初始化 GPIO16: `$ echo 16 > /sys/class/gpio/export` 設定 GPIO16 為輸出: `$ echo out > /sys/class/gpio/gpio16/direction` 設定 GPIO16 為輸入: `$ echo in > /sys/class/gpio/gpio16/direction` 設定 GPIO16 為高電位: `$ echo 1 > /sys/class/gpio/gpio16/value` 設定 GPIO16 為低電位: `$ echo 0 > /sys/class/gpio/gpio16/value` 查看 GPIO16 的數值: ``` $ cat /sys/class/gpio/gpio16/value $ cat /sys/kernel/debug/gpio ``` 解除 GPIO16 : `$ echo 16 > /sys/class/gpio/unexport` {% hint style="info" %} 當 GPIO16 初始化之後，`/sys/class/gpio/gpio16/`資料夾才建立，同時，只有在 GPIO16 設定為輸出後，才可以設定 GPIO 的數值，GPIO為輸入或是輸出會保留之前設定。在解除 GPIO 之後，資料夾也會移除。 {% endhint %} 可以參考以下資訊: * * 若是我們需要查看 GPIO 的目前設置，可以使用指令: `$ cat /sys/kernel/debug/gpio` ![GL-AR750S 的 GPIO 設置](/files/-LNsaq-hECKJm9Di65Ti) ## GPIO 輸出電壓值量測 當我們改變了 GPIO 輸出，在物理上就會改變其電壓數值，我們用電壓計來查詢改變後的電壓值，以下是我們的實驗內容，量測電位的的腳位可以參考"測試硬體與功能列表"的章節。 ![GPIO9 的低電位](/files/-LNsh12tUr-seGTZYk0q) ![GPIO9 的高電位](/files/-LNsh5mQxlwwKpJwMV-O) 以下是我們對 GL-AR300M 的測試結果。 | GL-AR300M | LOW | HIGH | | --------- | --- | ----- | | GPIO16 | 0V | 2.56V | | GPIO17 | 0V | 3.30V | | GPIO9 | 0V | 2.53V | | GPIO10 | 0V | 2.56V | ## 將分配給 I2C 的腳位改回 GPIO 在 GL-AR750S 這塊板子上，我們可以看到 I2C 已經預設開啟。因此，原本能夠使用的 GPIO，也只剩下 18、22，而5, 21被指定為 I2C 的通訊介面 (SDA、SCL)。 因此，若是要使用 GPIO 5 和21，則必須先把 I2C 的功能關閉，否則就無法 export。若我們需要將原本分配給 I2C 的腳位 (GPIO 5) 改回 GPIO，則可以使用以下指令: ``` root@GL-AR750S:~# echo "i2c-gpio.0" > /sys/bus/platform/drivers/i2c-gpio/unbind root@GL-AR750S:~# echo 5 > /sys/class/gpio/export root@GL-AR750S:~# cat /sys/class/gpio/gpio5/direction in root@GL-AR750S:~# echo out > /sys/class/gpio/gpio5/direction root@GL-AR750S:~# cat /sys/class/gpio/gpio5/value 0 root@GL-AR750S:~# echo 1 > /sys/class/gpio/gpio5/value root@GL-AR750S:~# cat /sys/class/gpio/gpio5/value 1 ``` 相同的，對 pin 21 也可以進行一樣的操作。 ``` root@GL-AR750S:~# echo 21 > /sys/class/gpio/export root@GL-AR750S:~# cat /sys/kernel/debug/gpio gpiochip0: GPIOs 0-31, parent: platform/ath79-gpio, ath79-gpio: gpio-1 ( |gl-ar750s:white:powe) out lo gpio-2 ( |reset ) in hi gpio-5 ( |sysfs ) out hi gpio-7 ( |gl-ar750s:white:usbp) out hi gpio-8 ( |right ) in hi gpio-19 ( |gl-ar750s:white:wlan) out hi gpio-20 ( |gl-ar750s:white:wlan) out hi gpio-21 ( |sysfs ) in hi gpio-22 ( |sysfs ) out hi gpiochip1: GPIOs 489-511, parent: platform/qca956x_wmac, ath9k-phy1: gpio-490 ( |ath9k-phy1 ) in lo ``` 重開機之後，就重新回到分配給 I2C 的設定: ``` root@GL-AR750S:~# cat /sys/kernel/debug/gpio gpiochip0: GPIOs 0-31, parent: platform/ath79-gpio, ath79-gpio: gpio-1 ( |gl-ar750s:white:powe) out lo gpio-2 ( |reset ) in hi gpio-5 ( |sda ) in hi gpio-7 ( |gl-ar750s:white:usbp) out hi gpio-8 ( |right ) in hi gpio-19 ( |gl-ar750s:white:wlan) out lo gpio-20 ( |gl-ar750s:white:wlan) out hi gpio-21 ( |scl ) in hi gpiochip1: GPIOs 489-511, parent: platform/qca956x_wmac, ath9k-phy1: gpio-490 ( |ath9k-phy1 ) in lo ``` 我們可以寫一隻簡單的 script 來進行設定 unbind I2C 的設定，並測試 GPIO 的寫入結果。 ``` echo "i2c-gpio.0" > /sys/bus/platform/drivers/i2c-gpio/unbind echo 5 > /sys/class/gpio/export echo 18 > /sys/class/gpio/export echo 21 > /sys/class/gpio/export echo 22 > /sys/class/gpio/export echo out > /sys/class/gpio/gpio5/direction echo out > /sys/class/gpio/gpio18/direction echo out > /sys/class/gpio/gpio21/direction echo out > /sys/class/gpio/gpio22/direction echo "===== all gpio {5,18,21,22} set to LOW =====" echo 0 > /sys/class/gpio/gpio5/value echo 0 > /sys/class/gpio/gpio18/value echo 0 > /sys/class/gpio/gpio21/value echo 0 > /sys/class/gpio/gpio22/value cat /sys/kernel/debug/gpio echo "===== all gpio {5,18,21,22} set to HIGH =====" echo 1 > /sys/class/gpio/gpio5/value echo 1 > /sys/class/gpio/gpio18/value echo 1 > /sys/class/gpio/gpio21/value echo 1 > /sys/class/gpio/gpio22/value cat /sys/kernel/debug/gpio ``` 結果顯示， AR750S 的 GPIO {5、18、21} 腳位沒有問題，但是， GPIO 22 腳位無法寫入為 LOW 的數值。 ``` # sh unbindi2c.sh ===== all gpio {5,18,21,22} set to LOW ===== gpiochip0: GPIOs 0-31, parent: platform/ath79-gpio, ath79-gpio: gpio-1 ( |gl-ar750s:white:powe) out lo gpio-2 ( |reset ) in hi gpio-5 ( |sysfs ) out lo gpio-7 ( |gl-ar750s:white:usbp) out hi gpio-8 ( |right ) in hi gpio-18 ( |sysfs ) out lo gpio-19 ( |gl-ar750s:white:wlan) out lo gpio-20 ( |gl-ar750s:white:wlan) out hi gpio-21 ( |sysfs ) out lo gpio-22 ( |sysfs ) out hi gpiochip1: GPIOs 489-511, parent: platform/qca956x_wmac, ath9k-phy1: gpio-490 ( |ath9k-phy1 ) in lo ===== all gpio {5,18,21,22} set to HIGH ===== gpiochip0: GPIOs 0-31, parent: platform/ath79-gpio, ath79-gpio: gpio-1 ( |gl-ar750s:white:powe) out lo gpio-2 ( |reset ) in hi gpio-5 ( |sysfs ) out hi gpio-7 ( |gl-ar750s:white:usbp) out hi gpio-8 ( |right ) in hi gpio-18 ( |sysfs ) out hi gpio-19 ( |gl-ar750s:white:wlan) out lo gpio-20 ( |gl-ar750s:white:wlan) out hi gpio-21 ( |sysfs ) out hi gpio-22 ( |sysfs ) out hi gpiochip1: GPIOs 489-511, parent: platform/qca956x_wmac, ath9k-phy1: gpio-490 ( |ath9k-phy1 ) in lo ``` 以下是我們對 GL-AR750S 的電壓測試結果。 | GL-AR750S | LOW | HIGH | | ------------ | --- | ----- | | GPIO5 (SDA) | 0V | 2.56V | | GPIO18 | 0V | 2.56V | | GPIO21 (SCL) | 0V | 2.34V | | GPIO22 | -- | 2.56V | --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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