--- title: General-purpose Input/Output (GPIO) categories: GPIO, STM32F4 ... Introduction ============ **General Purpose Input/Output (GPIO)** is a generic pin on a chip whose behavior (including whether it is an input or output pin) can be controlled (programmed) by the user at run time. 通常我們program使用的data都是放在memory比較多,而GPIO也提供類似的操作方法給programmer(讓我們去更改記憶體內容就可以去控制pin,並影響周遭設備的運行),但真正的設備的位置並非真正落在記憶體上(如:LED、Button、...等),故GPIO的核心是記憶體操作與設備之間的一些電路特性。 Main Feature ============ GPIO雖然建立起記憶體與設備之間的橋梁,但也並非我們就可以隨意使用,我們必須要經過設定之後才能讓我們想要的設備正常工作。 一個pin一次只能被設定成是input或output,而input會有三種狀態表現(floating, pull-up/down, analog),而output只有兩種狀態表現(push-pull or open drain + pull-up/down)。 - input/output方向解說 : input是指記憶體方接收來自設備的訊號源,output是指記憶體傳送訊號給設備。 當pin被設定成input時,非analog的設定下,我們可以利用GPIO的input data register(GPIOx_IDR) 或是memory中提供給目標設備的data register (當設成alternate function的時候)去接收data。 當pin被設定成output時,非analog的設定下,GPIO本身有提供output data register (GPIOx_ODR)來對目標設備做控制,但要是pin不是使用原本預先定義好的功能時(非預先定義的功能都算是alternate function的類別),此時要用memory中,另外規劃給目標設備用的register。 如果pin被設成analog的話,無論input or output都會由adc那邊做處理。 Functional Description ====================== input ------------------- - floating vs. pull-up/pull-down 當input pin被處在高阻抗的模式下,若沒有外部訊號源進來的話,此時是無法確定pin的狀態(不能確定現在處在高電位或低電位),除非有外部訊號來驅動電路。換句話說,input floating,這個input電位狀態完全是由外部訊號來決定,沒有訊號驅動的話,就會呈現高阻抗狀態。 剛剛提到floating在沒有外部訊號驅動的情況下是呈現高阻抗狀態(無法確定電位狀態=>不能明確表示現在值是0或1),如果我們需要這個pin有一個明確的預設狀態時,必須借助pull-up(pull-down)resistor來做調整,在pull-up resistor(pull-up外接高電壓,pull-down通常會接地)加入之下,讓pin的維持在明確的高電壓狀態(pull-down則是讓pin維持在低電壓狀態)。舉例來說,如果我們定電壓在3-4 V之間是1的狀態,0-1之間是0的狀態,高阻抗的時候,電壓是不明確的,有可能電壓值會落在1-3之間的不明確地帶,甚至是沒有在任何一個狀態維持一段時間,此時的狀態是未定的,但如果我們加入pull-up resistor的話,這個pin接受來自pull-up另一端的電壓供應,讓pin至少維持在3v以上時,我們就可以確定在沒有外部訊號驅動時,pin是維持在高電位狀態。 output ------------------- - push-pull vs. open-drain with pull-up/pull-down analog ------------------- 前面所述的input/output跟現在要談的類比模式是跟是不一樣的類型,前者的資料型態主要是高低電位的數位型態(0/1的分別),而類比訊號是普遍自然界的訊號型態,故當我們設定成類比輸入的模式時,進來GPIO pin的原始訊號源在還沒經過施密特觸發器(Schmitt trigger)會有另一個線路將訊號做導向(通常是要導到ADC去),另一方面,當我們用了類比輸出模式後,GPIO的內部將會有一條線路接收DAC處理完的類比訊號,在經過此pin傳遞到外部去。 - 施密特觸發器(Schmitt trigger) : 將類比訊號的波形整成數位電路所能處理的方波波形(處理完只能分辨出高低電位的差別)。 .. image:: /embedded/Schmitt_trigger.jpg (施密特觸發器具有整流效果) basic of structure (P.186, **Figure 17. Basic structure of a five-volt tolerant I/O port bit** in Reference manual) ------------------------------------------------------------------------------------------------------------------- .. image:: /embedded/GPIO_basic_src.PNG Vdd : 一個供電來源,電壓介在1.7 V - 3.6V之間 Vdd_ft : 5-volt tolerant用的供電來源。 Configuration ============= Input configuration (P.193, **7.3.9 Input configuration** in Reference manual) ------------------------------------------------------------------------------ When the I/O port is programmed as Input: - the output buffer is disabled - the Schmitt trigger input is activated - 這種模式處理的數位訊號只在意高低電位的差別(開關控制)。 - the pull-up and pull-down resistors are activated depending on the value in the GPIOx_PUPDR register - 想要讓pin的state變成一個確定的狀態,可以設定pull-up/pull-down的使用。 - The data present on the I/O pin are sampled into the input data register every AHB1 clock cycle - input data的更新主要就是以AHB1本身的更新週期做決定,每一個cycle抵達時,data register就會根據當時Schmitt trigger整流完的狀態做更新。 - A read access to the input data register provides the I/O State - 對data register的理解,我覺得用'狀態'比'數值'的敘述來的更好(大部分都是開關,就是外部訊號源是否有狀態改變,如 : button的按下與放開),而此處寫I/O state的意思是,即使我們現在是設成output(如 : LED控制),但我們仍然可用input data register來檢查LED現在的狀態。 Output configuration (P.194, **7.3.10 Output configuration** in Reference manual) --------------------------------------------------------------------------------- When the I/O port is programmed as output: - The output buffer is enabled: - Open drain mode: A “0” in the Output register activates the N-MOS whereas a “1” in the Output register leaves the port in Hi-Z (the P-MOS is never activated) - Push-pull mode: A “0” in the Output register activates the N-MOS whereas a “1” in the Output register activates the P-MOS - The Schmitt trigger input is activated - The weak pull-up and pull-down resistors are activated or not depending on the value in the GPIOx_PUPDR register - The data present on the I/O pin are sampled into the input data register every AHB1 clock cycle - A read access to the input data register gets the I/O state - A read access to the output data register gets the last written value Alternate function configuration (P.195, **7.3.11 Alternate function configuration** in Reference manual) --------------------------------------------------------------------------------------------------------- When the I/O port is programmed as alternate function: - The output buffer can be configured as open-drain or push-pull - The output buffer is driven by the signal coming from the peripheral (transmitter enable and data) - The Schmitt trigger input is activated - The weak pull-up and pull-down resistors are activated or not depending on the value in the GPIOx_PUPDR register - The data present on the I/O pin are sampled into the input data register every AHB1 clock cycle - A read access to the input data register gets the I/O state Remark: GPIOx_AFRL[31:0] and GPIOx_ARHL[31:0] provide ways to select alternation functions. However, different alternate functions maps to different bits of ports. Table below is part of alternate function mapping, which is mainly about USART2/3. For more information, please refer to **Table 8. Alternate function mapping** from P.58-62 in STM32F407xx Datasheet. .. image:: /embedded/af_mapping.png Analog configuration (P.196, **7.3.12 Analog configuration** in Reference manual) --------------------------------------------------------------------------------- When the I/O port is programmed as analog configuration: - The output buffer is disabled - The Schmitt trigger input is deactivated, providing zero consumption for every analog value of the I/O pin. The output of the Schmitt trigger is forced to a constant value (0). - The weak pull-up and pull-down resistors are disabled - Read access to the input data register gets the value “0” Note: In the analog configuration, the I/O pins cannot be 5 Volt tolerant. Demo ==== 工具介紹 ------- .. image:: /embedded/BNC line.JPG - BNC對鱷魚夾線 .. image:: /embedded/oscilloscope.JPG - 示波器(oscilloscope) 畫面很差... 示波器驗證 --------- .. image:: /embedded/stable.JPG - 示波器我們調整的scale是1 volt為單位。 - 我們接線是使用BNC對鱷魚夾線,黑接Groud,紅接要觀察的Pin。此圖為我們還沒做任何操作呈現的狀態。 .. image:: /embedded/button_pressed.JPG - 以button做為觀察GPIO input的部份 - USER button對應的腳位為PA0 - 按下button馬上放開後會產生一個小方波,由此可知,按下button是產生高電位訊號。(看'按下'多久高電位就維持多久) .. image:: /embedded/LEDOn_2.8v.JPG - 用LED4來觀察GPIO output的部份 - LED4對應的腳位是PD12,當LED4亮的時候,我們可以看到波形產生變化(從0v左右的位置升到高電位2.8v左右) .. image:: /embedded/PD12_PD14CNT.JPG - 我們在接Pin的過程的時候,發現有些燈會亮起來,圖中紅色鱷魚夾線把PD12跟PD14同時夾起來,LED5在LED4亮起來的時候也會亮,對照PD14的位置是LED5。 - 我們觀察示波器用的Code只有對button跟LED4做設定,我們推測原因是LED4亮起來的時候,PD12處於高電位狀態,而鱷魚夾線連通PD14讓此腳位也處於高電位使LED5也亮起來了。 Code Section ------------- sample code download : .. code-block:: c git clone git://gitcafe.com/akasha00/stm32_GPIO_demo.git cd stm32_GPIO_demo/ test for code : .. code-block:: c make make flash 測試方法 : - input使用button作為範例,output是LED控制。 stm32f4_discovery library的預先定義(in libstm/Utilities/STM32F4-Discovery/stm32f4_discovery.h) : .. code-block:: c #define LEDn 4 #define LED4_PIN GPIO_Pin_12 #define LED4_GPIO_PORT GPIOD #define LED4_GPIO_CLK RCC_AHB1Periph_GPIOD #define LED3_PIN GPIO_Pin_13 #define LED3_GPIO_PORT GPIOD #define LED3_GPIO_CLK RCC_AHB1Periph_GPIOD #define LED5_PIN GPIO_Pin_14 #define LED5_GPIO_PORT GPIOD #define LED5_GPIO_CLK RCC_AHB1Periph_GPIOD #define LED6_PIN GPIO_Pin_15 #define LED6_GPIO_PORT GPIOD #define LED6_GPIO_CLK RCC_AHB1Periph_GPIOD #define BUTTONn 1 #define USER_BUTTON_PIN GPIO_Pin_0 #define USER_BUTTON_GPIO_PORT GPIOA #define USER_BUTTON_GPIO_CLK RCC_AHB1Periph_GPIOA #define USER_BUTTON_EXTI_LINE EXTI_Line0 #define USER_BUTTON_EXTI_PORT_SOURCE EXTI_PortSourceGPIOA #define USER_BUTTON_EXTI_PIN_SOURCE EXTI_PinSource0 #define USER_BUTTON_EXTI_IRQn EXTI0_IRQn - LED是屬於GPIO port D,第12-15個pin分別是控制,LED4、LED3、LED5、LED6。 - Button是屬於GPIO port A,第0個pin是可以用來檢查button狀態的腳位。在文件中,有時會看到Wake-up button這一名稱,其實就是在說User button,兩者是指同一個東西。 input 設定 : - button initialization(in libstm/Utilities/STM32F4-Discovery/stm32f4_discovery.c) : .. code-block:: c void STM_EVAL_PBInit(Button_TypeDef Button, ButtonMode_TypeDef Button_Mode) { GPIO_InitTypeDef GPIO_InitStructure; EXTI_InitTypeDef EXTI_InitStructure; NVIC_InitTypeDef NVIC_InitStructure; /* 要設定好Clock才能正確更新Button的State,BUTTON_CLK[Button]是指RCC_AHB1Periph_GPIOA */ RCC_AHB1PeriphClockCmd(BUTTON_CLK[Button], ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_SYSCFG, ENABLE); /* 設定為input mode,我們不給pin任何預設狀態,所PuPd的部份設成NOPULL */ GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN; GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL; GPIO_InitStructure.GPIO_Pin = BUTTON_PIN[Button]; GPIO_Init(BUTTON_PORT[Button], &GPIO_InitStructure); if (Button_Mode == BUTTON_MODE_EXTI) { /* 啟用interrupt並建立好與button腳位的連結 */ SYSCFG_EXTILineConfig(BUTTON_PORT_SOURCE[Button], BUTTON_PIN_SOURCE[Button]); /* Configure Button EXTI line */ EXTI_InitStructure.EXTI_Line = BUTTON_EXTI_LINE[Button]; EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt; EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising; EXTI_InitStructure.EXTI_LineCmd = ENABLE; EXTI_Init(&EXTI_InitStructure); /* Enable and set Button EXTI Interrupt to the lowest priority */ NVIC_InitStructure.NVIC_IRQChannel = BUTTON_IRQn[Button]; NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0F; NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0F; NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; NVIC_Init(&NVIC_InitStructure); } } - Button interrupt handler(in main.c) .. code-block:: c void EXTI0_IRQHandler(void) { /* 當Button按下後觸發interrupt,用自定義變數紀錄Button state的改變。 */ UserButtonPressed = 0x01; /* Clear the EXTI line pending bit */ EXTI_ClearITPendingBit(USER_BUTTON_EXTI_LINE); } output 設定 : - LED initialization (in libstm/Utilities/STM32F4-Discovery/stm32f4_discovery.c) : .. code-block:: c void STM_EVAL_LEDInit(Led_TypeDef Led) { GPIO_InitTypeDef GPIO_InitStructure; /* LED是屬於Port D,要設定好Clk讓Port D可以正確被更新 */ RCC_AHB1PeriphClockCmd(GPIO_CLK[Led], ENABLE); /* 設定各LED對應的腳位,output type設成push-pull,並使用pull-up電阻,LED初始化完成時,會呈現高電位狀態(亮燈)。 */ GPIO_InitStructure.GPIO_Pin = GPIO_PIN[Led]; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT; GPIO_InitStructure.GPIO_OType = GPIO_OType_PP; GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(GPIO_PORT[Led], &GPIO_InitStructure); } main.c : - main function : .. code-block:: c int main(void) { RCC_ClocksTypeDef RCC_Clocks; /* button初始化,並使用interrupt。 */ STM_EVAL_PBInit(BUTTON_USER, BUTTON_MODE_EXTI); /* 初始化需要用到的LED。 */ STM_EVAL_LEDInit(LED4); STM_EVAL_LEDInit(LED3); STM_EVAL_LEDInit(LED5); STM_EVAL_LEDInit(LED6); /* 初始化有使用到pull-up電阻,預設會亮燈,在這邊把燈關掉。 */ STM_EVAL_LEDOff(LED4); STM_EVAL_LEDOff(LED3); STM_EVAL_LEDOff(LED5); STM_EVAL_LEDOff(LED6); /* 初始化自定義變數 */ UserButtonPressed = 0x00; /* Create a task to flash the LED. */ xTaskCreate(LED_task, (signed portCHAR *) "LED Flash", 512 /* stack size */, NULL, tskIDLE_PRIORITY + 5, NULL); /* Create a task to button check. */ xTaskCreate(button_task, (signed portCHAR *) "User Button", 512 /* stack size */, NULL, tskIDLE_PRIORITY + 5, NULL); /* Start running the tasks. */ vTaskStartScheduler(); return 0; } - LED control task .. code-block:: c static void LED_task(void *pvParameters) { RCC_ClocksTypeDef RCC_Clocks; uint8_t togglecounter = 0x00; while(1) { /* Toggle LED5 */ STM_EVAL_LEDToggle(LED5); vTaskDelay(100); /* Toggle LED6 */ STM_EVAL_LEDToggle(LED6); vTaskDelay(100); } } - Button check task : .. code-block:: c static void button_task(void *pvParameters) { while (1) { /* Waiting User Button is pressed */ if (UserButtonPressed == 0x01) { /* Toggle LED4 */ STM_EVAL_LEDToggle(LED4); vTaskDelay(100); /* Toggle LED3 */ STM_EVAL_LEDToggle(LED3); vTaskDelay(100); } /* Waiting User Button is Released */ while (STM_EVAL_PBGetState(BUTTON_USER) == Bit_SET); UserButtonPressed = 0x00; } } Supplement ========== - 一些有預設控制元件的腳位(詳見- STM32F4-Discovery 中文使用手冊P.16) - LD3:橙色,連接到STM32F407VGT6的PD13 - LD4:綠色,連接到STM32F407VGT6的PD12 - LD5:红色,連接到STM32F407VGT6的PD14 - LD6:藍色,連接到STM32F407VGT6的PD15 - B1(USER):連接到STM32F407VGT6的PA0 - B2(RESET):連接到NRST,用於重置STM32F407VGT6 Reference ========= - `General Purpose Input/Output - Wikipedia, the free encyclopedia `_ - `STM32F407xx Datasheet`_ - `STM32F407xx Reference Manual`_ - `STM32F4-Discovery 中文使用手冊`_ - `稀里糊塗學 STM32 第二講:源源不絕`_ - `GPIO PPT`_