本文來源電子發燒友社區，作者：華仔stm32， 帖子地址：https://bbs.elecfans.com/jishu_2299452_1_1.html


在前面驅動OLED的前提下，驅動AHT20并顯示到顯示屏，是監測溫濕度常用的手法。
1、在app目錄下新建i2caht20文件夾，把oled_ssd1306.c以及oled_ssd1306.h拷貝到該目錄下。
2、新建aht20.c、aht20.h，以及aht20.test.c,以及BUILD.gn三個文件。
3、aht20.c內容如下：

/*
 * Copyright (C) 2021 HiHope Open Source Organization .
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 *
 * limitations under the License.
 */

#include "aht20.h"

#include 
#include 
#include 

#include "hi_i2c.h"
#include "hi_errno.h"

#define AHT20_I2C_IDX HI_I2C_IDX_0

#define AHT20_STARTUP_TIME     20*1000 // 上電啟動時間
#define AHT20_CALIBRATION_TIME 40*1000 // 初始化（校準）時間
#define AHT20_MEASURE_TIME     75*1000 // 測量時間

#define AHT20_DEVICE_ADDR   0x38
#define AHT20_READ_ADDR     ((0x38<<1)|0x1)
#define AHT20_WRITE_ADDR    ((0x38<<1)|0x0)

#define AHT20_CMD_CALIBRATION       0xBE // 初始化（校準）命令
#define AHT20_CMD_CALIBRATION_ARG0  0x08
#define AHT20_CMD_CALIBRATION_ARG1  0x00

/**
 * 傳感器在采集時需要時間,主機發出測量指令（0xAC）后，延時75毫秒以上再讀取轉換后的數據并判斷返回的狀態位是否正常。
 * 若狀態比特位[Bit7]為0代表數據可正常讀取，為1時傳感器為忙狀態，主機需要等待數據處理完成。
 **/
#define AHT20_CMD_TRIGGER       0xAC // 觸發測量命令
#define AHT20_CMD_TRIGGER_ARG0  0x33
#define AHT20_CMD_TRIGGER_ARG1  0x00

// 用于在無需關閉和再次打開電源的情況下，重新啟動傳感器系統，軟復位所需時間不超過20 毫秒
#define AHT20_CMD_RESET      0xBA // 軟復位命令

#define AHT20_CMD_STATUS     0x71 // 獲取狀態命令

/**
 * STATUS 命令回復：
 * 1. 初始化后觸發測量之前，STATUS 只回復 1B 狀態值；
 * 2. 觸發測量之后，STATUS 回復6B： 1B 狀態值 + 2B 濕度 + 4b濕度 + 4b溫度 + 2B 溫度
 *      RH = Srh / 2^20 * 100%
 *      T  = St  / 2^20 * 200 - 50
 **/
#define AHT20_STATUS_BUSY_SHIFT 7       // bit[7] Busy indication
#define AHT20_STATUS_BUSY_MASK  (0x1<#define AHT20_STATUS_BUSY(status) ((status & AHT20_STATUS_BUSY_MASK) >> AHT20_STATUS_BUSY_SHIFT)

#define AHT20_STATUS_MODE_SHIFT 5       // bit[6:5] Mode Status
#define AHT20_STATUS_MODE_MASK  (0x3<#define AHT20_STATUS_MODE(status) ((status & AHT20_STATUS_MODE_MASK) >> AHT20_STATUS_MODE_SHIFT)

                                        // bit[4] Reserved
#define AHT20_STATUS_CALI_SHIFT 3       // bit[3] CAL Enable
#define AHT20_STATUS_CALI_MASK  (0x1<#define AHT20_STATUS_CALI(status) ((status & AHT20_STATUS_CALI_MASK) >> AHT20_STATUS_CALI_SHIFT)
                                        // bit[2:0] Reserved

#define AHT20_STATUS_RESPONSE_MAX 6

#define AHT20_RESOLUTION            (1<<20)  // 2^20

#define AHT20_MAX_RETRY 10

static uint32_t AHT20_Read(uint8_t* buffer, uint32_t buffLen)
{
    hi_i2c_data data = { 0 };
    data.receive_buf = buffer;
    data.receive_len = buffLen;
    uint32_t retval = hi_i2c_read(AHT20_I2C_IDX, AHT20_READ_ADDR, &data);
    if (retval != HI_ERR_SUCCESS) {
        printf("I2cRead() failed, %0X!n", retval);
        return retval;
    }
    return HI_ERR_SUCCESS;
}

static uint32_t AHT20_Write(uint8_t* buffer, uint32_t buffLen)
{
    hi_i2c_data data = { 0 };
    data.send_buf = buffer;
    data.send_len = buffLen;
    uint32_t retval = hi_i2c_write(AHT20_I2C_IDX, AHT20_WRITE_ADDR, &data);
    if (retval != HI_ERR_SUCCESS) {
        printf("I2cWrite(%02X) failed, %0X!n", buffer[0], retval);
        return retval;
    }
    return HI_ERR_SUCCESS;
}

// 發送獲取狀態命令
static uint32_t AHT20_StatusCommand(void)
{
    uint8_t statusCmd[] = { AHT20_CMD_STATUS };
    return AHT20_Write(statusCmd, sizeof(statusCmd));
}

// 發送軟復位命令
static uint32_t AHT20_ResetCommand(void)
{
    uint8_t resetCmd[] = {AHT20_CMD_RESET};
    return AHT20_Write(resetCmd, sizeof(resetCmd));
}

// 發送初始化校準命令
static uint32_t AHT20_CalibrateCommand(void)
{
    uint8_t clibrateCmd[] = {AHT20_CMD_CALIBRATION, AHT20_CMD_CALIBRATION_ARG0, AHT20_CMD_CALIBRATION_ARG1};
    return AHT20_Write(clibrateCmd, sizeof(clibrateCmd));
}

// 讀取溫濕度值之前， 首先要看狀態字的校準使能位Bit[3]是否為 1(通過發送0x71可以獲取一個字節的狀態字)，
// 如果不為1，要發送0xBE命令(初始化)，此命令參數有兩個字節， 第一個字節為0x08，第二個字節為0x00。
uint32_t AHT20_Calibrate(void)
{
    uint32_t retval = 0;
    uint8_t buffer[AHT20_STATUS_RESPONSE_MAX];
    memset(&buffer, 0x0, sizeof(buffer));

    retval = AHT20_StatusCommand();
    if (retval != HI_ERR_SUCCESS) {
        return retval;
    }

    retval = AHT20_Read(buffer, sizeof(buffer));
    if (retval != HI_ERR_SUCCESS) {
        return retval;
    }

    if (AHT20_STATUS_BUSY(buffer[0]) || !AHT20_STATUS_CALI(buffer[0])) {
        retval = AHT20_ResetCommand();
        if (retval != HI_ERR_SUCCESS) {
            return retval;
        }
        usleep(AHT20_STARTUP_TIME);
        retval = AHT20_CalibrateCommand();
        usleep(AHT20_CALIBRATION_TIME);
        return retval;
    }

    return HI_ERR_SUCCESS;
}

// 發送 觸發測量 命令，開始測量
uint32_t AHT20_StartMeasure(void)
{
    uint8_t triggerCmd[] = {AHT20_CMD_TRIGGER, AHT20_CMD_TRIGGER_ARG0, AHT20_CMD_TRIGGER_ARG1};
    return AHT20_Write(triggerCmd, sizeof(triggerCmd));
}

// 接收測量結果，拼接轉換為標準值
uint32_t AHT20_GetMeasureResult(float* temp, float* humi)
{
    uint32_t retval = 0, i = 0;
    if (temp == NULL || humi == NULL) {
        return HI_ERR_FAILURE;
    }

    uint8_t buffer[AHT20_STATUS_RESPONSE_MAX];
    memset(&buffer, 0x0, sizeof(buffer));
    retval = AHT20_Read(buffer, sizeof(buffer));  // recv status command result
    if (retval != HI_ERR_SUCCESS) {
        return retval;
    }

    for (i = 0; AHT20_STATUS_BUSY(buffer[0]) && i < AHT20_MAX_RETRY; i++) {
        // printf("AHT20 device busy, retry %d/%d!rn", i, AHT20_MAX_RETRY);
        usleep(AHT20_MEASURE_TIME);
        retval = AHT20_Read(buffer, sizeof(buffer));  // recv status command result
        if (retval != HI_ERR_SUCCESS) {
            return retval;
        }
    }
    if (i >= AHT20_MAX_RETRY) {
        printf("AHT20 device always busy!rn");
        return HI_ERR_SUCCESS;
    }

    uint32_t humiRaw = buffer[1];
    humiRaw = (humiRaw << 8) | buffer[2];
    humiRaw = (humiRaw << 4) | ((buffer[3] & 0xF0) >> 4);
    *humi = humiRaw / (float)AHT20_RESOLUTION * 100;

    uint32_t tempRaw = buffer[3] & 0x0F;
    tempRaw = (tempRaw << 8) | buffer[4];
    tempRaw = (tempRaw << 8) | buffer[5];
    *temp = tempRaw / (float)AHT20_RESOLUTION * 200 - 50;
    // printf("humi = %05X, %f, temp= %05X, %frn", humiRaw, *humi, tempRaw, *temp);
    return HI_ERR_SUCCESS;
}
)<>)<>)<>

4、aht20.h內容如下：

/*
 * Copyright (C) 2021 HiHope Open Source Organization .
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 *
 * limitations under the License.
 */

#ifndef AHT20_H
#define AHT20_H

#include 

uint32_t AHT20_Calibrate(void);

uint32_t AHT20_StartMeasure(void);

uint32_t AHT20_GetMeasureResult(float* temp, float* humi);

#endif  // AHT20_H

5、aht20_test.c內容如下：

/*
 * Copyright (C) 2021 HiHope Open Source Organization .
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 *
 * limitations under the License.
 */

#include "aht20.h"

#include 
#include 

#include "ohos_init.h"
#include "cmsis_os2.h"
#include "hi_gpio.h"
#include "hi_io.h"
#include "hi_i2c.h"
#include "oled_ssd1306.h"

void Aht20TestTask(void* arg)
{
    (void) arg;
    uint32_t retval = 0;
    char str_temp[12];
    char str_Humi[12];
    hi_io_set_func(HI_IO_NAME_GPIO_13, HI_IO_FUNC_GPIO_13_I2C0_SDA);
    hi_io_set_func(HI_IO_NAME_GPIO_14, HI_IO_FUNC_GPIO_14_I2C0_SCL);

    hi_i2c_init(HI_I2C_IDX_0, 400*1000);
    OledInit();

    OledFillScreen(0x00);  
    OledShowString(26, 0, "AHT20-TEST!", FONT8x16);
    retval = AHT20_Calibrate();
    printf("AHT20_Calibrate: %drn", retval);

    while (1) {
        float temp = 0.0, humi = 0.0;
        
        retval = AHT20_StartMeasure();
        printf("AHT20_StartMeasure: %drn", retval);

        retval = AHT20_GetMeasureResult(&temp, &humi);
        sprintf(str_temp,"TEMP:%.2f",temp);
        sprintf(str_Humi,"HUMI:%.2f",humi);
        printf("AHT20_GetMeasureResult: %d, temp = %.2f, humi = %.2frn", retval, temp, humi);
        OledShowString(26,2,str_temp,FONT8x16);
        OledShowString(26,4,str_Humi,FONT8x16);
        sleep(1);
    }
}

void Aht20Test(void)
{
    osThreadAttr_t attr;

    attr.name = "Aht20Task";
    attr.attr_bits = 0U;
    attr.cb_mem = NULL;
    attr.cb_size = 0U;
    attr.stack_mem = NULL;
    attr.stack_size = 4096;
    attr.priority = osPriorityNormal;

    if (osThreadNew(Aht20TestTask, NULL, &attr) == NULL) {
        printf("[Aht20Test] Failed to create Aht20TestTask!n");
    }
}

APP_FEATURE_INIT(Aht20Test);

7、BUILD.gn:

#Copyright (C) 2021 HiHope Open Source Organization .
#Licensed under the Apache License, Version 2.0 (the "License");
#you may not use this file except in compliance with the License.
#You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
#Unless required by applicable law or agreed to in writing, software
#distributed under the License is distributed on an "AS IS" BASIS,
#WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#See the License for the specific language governing permissions and
#
#limitations under the License.

static_library("i2cd_emo") {
    sources = [
        "aht20_test.c",
        "aht20.c",
        "oled_ssd1306.c"
    ]

    include_dirs = [
        "http://utils/native/lite/include",
        "http://kernel/liteos_m/components/cmsis/2.0",
        "http://base/iot_hardware/peripheral/interfaces/kits",
        "http://device/hisilicon/hispark_pegasus/sdk_liteos/include"
    ]
}

8、修改app/BUILD.gn如下：

import("http://build/lite/config/component/lite_component.gni")

lite_component("app") {
    features = [
        "i2caht20:i2cd_emo",
    ]
}

然后就可以編譯下載了。
運行效果如下圖：