如何在Linux应用层中使用i2c接口驱动外围芯片
目录
前言
1 detect内核中i2c模块
1.1 查看内核中I2C驱动
1.2 查看单个i2总线下设备地址
2 硬件电路
2.1 SHT-20模块电路
2.2 板卡上的i2c接口
3 开发环境
3.1 硬件系统参数
3.2 编译环境：Ubuntu
4 驱动程序实现
4.1 sht-20驱动代码
4.2 编写应用程序
4.3 编写Makefile
5 验证
6 逻辑分析仪查看波形
前言
本文主要介绍如何在应用层，调用内核中的I2C模块来驱动外围芯片，并且能正确的从这些芯片读取数据。文章以sht-20温湿度传感器为例，详细介绍I2C驱动接口的使用方法。
1 detect内核中i2c模块
1.1 查看内核中I2C驱动
进入/dev/目录下，可以看见，有两个驱动接口，i2c-0和i2c-1
可以使用i2c-tools工具，来查看每个i2c总线下设备的情况
1.2 查看单个i2总线下设备地址
1 ）查看i2c-0下设备情况
使用命令： i2cdetect -a 0
该i2c总线下有两个设备，其地址分别为：0x1a和0x1e
2 ) 查看i2c-1下设备情况
使用命令： i2cdetect -a 1
该i2c总线下有两个设备，其地址分别为：0x40和0x50
地址0x40: 对应的设备是sht-20温湿度传感器
地址0x50：是AT24C02芯片
2 硬件电路
2.1 SHT-20模块电路
1）SHT20硬件接口图
2) sensor模块电路
2.2 板卡上的i2c接口
本文做测试时，使用的i2c接口位置
电路实物图如下：
SHT-20实物图：
3 开发环境
3.1 硬件系统参数
硬件: ATK-DL6Y2C开发板(芯片型号： IMX6ULL）
内核启动位置： eMMC
3.2 编译环境：Ubuntu
版本信息: 20.04.2
Linux version 5.15.0-84-generic (buildd@lcy02-amd64-005) (gcc (Ubuntu 9.4.0-1ubuntu1~20.04.2) 9.4.0, GNU ld (GNU Binutils for Ubuntu) 2.34) #93~20.04.1-Ubuntu SMP Wed Sep 6 16:15:40 UTC 2023
linux kernel 版本信息： 4.1.15
Linux内核: linux-imx-4.1.15-2.1.0-g3dc0a4b-v2.7.tar.bz2
交叉编译器版本信息： gcc version 4.9.4
4 驱动程序实现
4.1 sht-20驱动代码
由于sht-20挂载在i2c-1上，所以，在驱动程序中直接调用i2c-1可操作sht-20的寄存器，其具体驱动代码如下：
/***************************************************************
Copyright 2024-2029. All rights reserved.
文件名 : drv_sht20.c
作者 : [email protected]
版本 : V1.0
描述 : sht-20 驱动程序
其他 : 无
日志 : 初版V1.0 2024/02/01
***************************************************************/
#include "drv-sht20.h"
/******************************************************************************
* LOCAL MACROS AND DEFINITIONS
******************************************************************************/
#define SHT2X_ADDR 0x40
#define POLY 0x131 //P(x)=x^8+x^5+x^4+1 = 100110001
#define DELAY_CNT 4500 //for N32G45, sleep time is 6.4 ms
#define DEV_FILE "/dev/i2c-1"
#define QUERY_TEMP_CMD TRIG_T_MEASUREMENT_POLL
#define QUERY_HUMIDY_CMD TRIG_RH_MEASUREMENT_POLL
static int public_fd;
static void msleep(unsigned int time)
{
struct timespec sleeper, temp;
sleeper.tv_sec = (time_t)(time/1000);
sleeper.tv_nsec = (long)(time%1000)*1000000;
nanosleep(&sleeper, &temp);
}
static int sht2xdrv_CheckCrc(unsigned char data[], unsigned char nbrOfBytes, unsigned char checksum)
{
int set = 0;
unsigned char crc = 0;
unsigned char byteCtr;
unsigned char bit;
//calculates 8-Bit checksum with given polynomial
for (byteCtr = 0; byteCtr < nbrOfBytes; ++byteCtr)
{
crc ^= (data[byteCtr]);
for ( bit = 8; bit > 0; --bit)
{
if (crc & 0x80)
{
crc = (crc << 1) ^ POLY;
}
else
{
crc = (crc << 1);
}
}
}
if (crc != checksum)
{
set = -1;
}
return set;
}
static int sht2xdrv_CalcTemperatureC(unsigned short u16sT)
{
int temperatureC; // variable for result
u16sT &= ~0x0003; // clear bits [1..0] (status bits)
/*
* Formula T = -46.85 + 175.72 * ST / 2^16 from data sheet 6.2,
* optimized for integer fixed point (3 digits) arithmetic
*/
temperatureC = ((17572 * u16sT) >> 16) - 4685;
return temperatureC;
}
static int sht2xdrv_CalcRH(unsigned short u16sRH)
{
int humidityRH; // variable for result
u16sRH &= ~0x0003; // clear bits [1..0] (status bits)
/*
* Formula RH = -6 + 125 * SRH / 2^16 from data sheet 6.1,
* optimized for integer fixed point (3 digits) arithmetic
*/
humidityRH = ((12500 * u16sRH) >> 16) - 600;
return humidityRH;
}
static int sht2x_send_cmd_wr( unsigned cmd)
{
int ret = -1;
unsigned char buf[2] = {0};
switch (cmd)
{
case QUERY_TEMP_CMD:
buf[0] = QUERY_TEMP_CMD;
ret = write(public_fd, buf, 1);
if( ret < 0 )
{
printf("write temper cmd to sht2x failure.\n");
return -1;
}
msleep(85); //datasheet typ=66, max=85
break;
case QUERY_HUMIDY_CMD:
buf[0] = QUERY_HUMIDY_CMD;
ret = write(public_fd, buf, 1);
if( ret < 0 )
{
printf("write humidity cmd to sht2x failure.\n");
return -1;
}
msleep(29); //datasheet typ=22, max=29
break;
default:
return -1;
}
return 0;
}
int sht2x_init(void)
{
int fd = -1;
fd = open(DEV_FILE, O_RDWR);
if( fd < 0 )
{
close( fd );
printf("%s %s i2c device open failure: %s\n", __FILE__, __FUNCTION__, strerror(errno));
return -1;
}
ioctl(fd, I2C_TENBIT, 0);
ioctl(fd, I2C_SLAVE, SHT2X_ADDR);
public_fd = fd;
return fd;
}
int sht2x_softreset( void )
{
int ret = -1;
unsigned char buf[2] = {0};
unsigned char cmd = SOFT_RESET;
buf[0] = cmd;
ret = write(public_fd, buf, 1);
if( ret < 0 )
{
printf("%s %s write softrest cmd to sht2x failure \n", __FILE__, __FUNCTION__);
return -1;
}
msleep(50);
return 0;
}
int sht2x_get_tempeture( float *temper)
{
unsigned char buf[4] = {0}, checksum;
int ret = -1;
int tempval;
ret = sht2x_send_cmd_wr( QUERY_TEMP_CMD);
if( ret < 0 )
{
return -1;
}
ret = read(public_fd, buf, 3);
if( ret < 0 )
{
printf("get the temper failure.\n");
return -1;
}
// match crc here
checksum = buf[2];
ret = sht2xdrv_CheckCrc(buf, 2, checksum);
if( ret < 0 )
{
printf("match check sum error.\n");
return -1;
}
tempval = (buf[0] << 8) | buf[1];
*temper = sht2xdrv_CalcTemperatureC( tempval );
return 0;
}
int sht2x_get_humidy( float *humidy )
{
unsigned char buf[4] = {0}, checksum;
int ret = -1;
int tempval;
ret = sht2x_send_cmd_wr( QUERY_HUMIDY_CMD );
if( ret < 0 )
{
return -1;
}
ret = read(public_fd, buf, 3);
if( ret < 0 )
{
printf("get the humidy failure.\n");
return -1;
}
// match crc here
checksum = buf[2];
ret = sht2xdrv_CheckCrc(buf, 2, checksum);
if( ret < 0 )
{
printf("match check sum error.\n");
return -1;
}
tempval = (buf[0] << 8) | buf[1];
*humidy = sht2xdrv_CalcRH( tempval );
return 0;
}
int sht2x_open( void )
{
int set;
set = sht2x_init();
if( set < 0 ){
return -1;
}
set = sht2x_softreset();
if( set < 0 ){
return -1;
}
return 0;
}
int sht2x_release( void )
{
close( public_fd );
return 0;
}
/** End of this file */
头文件部分代码：
#ifndef __DRV_SHT20_H
#define __DRV_SHT20_H
#ifdef __cplusplus
extern "C" {
#endif
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
typedef enum sht2xOptErrorCode
{
SHT2x_RES_I2C_ERR = 0X01,
}sht2xOptErrorCode;
/******************************************************************************
* EXPORTED MACROS AND DEFINITIONS
******************************************************************************/
typedef enum sht2xResolution_t
{
SHT2x_RES_12_14BIT = 0x00, // RH=12bit, T=14bit
SHT2x_RES_8_12BIT = 0x01, // RH= 8bit, T=12bit
SHT2x_RES_10_13BIT = 0x80, // RH=10bit, T=13bit
SHT2x_RES_11_11BIT = 0x81, // RH=11bit, T=11bit
SHT2x_RES_MASK = 0x81 // Mask for res. bits (7,0) in user reg.
} sht2xResolution_t;
typedef enum sht2xStatusCode {
SHT2x_STATUS_OK = 0x00,
SHT2x_STATUS_VALID_DATA = 0x01,
SHT2x_STATUS_NO_CHANGE = 0x02,
SHT2x_STATUS_ABORTED = 0x03,
SHT2x_STATUS_BUSY = 0x04,
SHT2x_STATUS_SUSPEND = 0x05,
SHT2x_STATUS_ERR_IO = 0x06,
SHT2x_STATUS_ERR_BAD_DATA = 0x07,
SHT2x_STATUS_ERR_TIMEOUT = 0x08
}sht2xStatusCode;
// sensor command
typedef enum{
TRIG_T_MEASUREMENT_HM = 0xE3, // command trig. temp meas. hold master
TRIG_RH_MEASUREMENT_HM = 0xE5, // command trig. humidity meas. hold master
TRIG_T_MEASUREMENT_POLL = 0xF3, // command trig. temp meas. no hold master
TRIG_RH_MEASUREMENT_POLL = 0xF5, // command trig. humidity meas. no hold master
USER_REG_W = 0xE6, // command writing user register
USER_REG_R = 0xE7, // command reading user register
SOFT_RESET = 0xFE // command soft reset
}sht2xCommand_t;
typedef enum {
SHT2x_EOB_ON = 0x40, // end of battery
SHT2x_EOB_MASK = 0x40, // Mask for EOB bit(6) in user reg.
} sht2xEob_t;
typedef enum {
SHT2x_HEATER_ON = 0x04, // heater on
SHT2x_HEATER_OFF = 0x00, // heater off
SHT2x_HEATER_MASK = 0x04, // Mask for Heater bit(2) in user reg.
} etSHT2xHeater;
// measurement signal selection
typedef enum{
HUMIDITY,
TEMP
}etSHT2xMeasureType;
typedef enum{
I2C_ADR_W = 128, // sensor I2C address + write bit
I2C_ADR_R = 129 // sensor I2C address + read bit
}etI2cHeader;
typedef struct {
unsigned char _step;
unsigned char ret;
unsigned char finish; //1: finished, 0: idle
unsigned char dataValid; //1: valid, 0: invalid
int _tryCnt;
int _binValue; // primordial value from sht20 register
int outValue; // true temperature or humidity
} shtdrv;
typedef struct {
shtdrv st_Temp;
shtdrv st_RH;
int errorCode;
}shtOpt;
int sht2x_open( void );
int sht2x_get_humidy( float *humidy );
int sht2x_get_tempeture( float *temper);
int sht2x_release( void );
#ifdef __cplusplus
}
#endif
#endif /* __DRV_SHT20_H */ 4.2 编写应用程序
该程序主要调用sht-20驱动程序中的接口，读取温湿度值。
/***************************************************************
Copyright 2024-2029. All rights reserved.
文件名 : test_sht20.c
作者 : [email protected]
版本 : V1.0
描述 : 验证dev_sht20.c
其他 : 无
日志 : 初版V1.0 2024/02/01
***************************************************************/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "drv-sht20.h"
int main(void)
{
float temper, rh;
int count_run = 100;
int set;
set = sht2x_open();
if( set < 0){
printf("initial sht20 failure.\n");
return -1;
}
while( count_run > 0){
set = sht2x_get_tempeture( &temper );
if(set > -1)
{
printf( "TM(C): %.2f ", temper*0.01);
}
set = sht2x_get_humidy( &rh );
if(set > -1)
{
printf("HM(\%): %.2f \r\n", rh*0.01);
}
count_run--;
}
sht2x_release();
return 0;
}
4.3 编写Makefile
CFLAGS= -Wall -O2
CC=/home/ctools/gcc-linaro-4.9.4-arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc
STRIP=/home/ctools/gcc-linaro-4.9.4-arm-linux-gnueabihf/bin/arm-linux-gnueabihf-strip
test-sht20: test-sht20.o drv-sht20.o
$(CC) $(CFLAGS) -o test-sht20 test-sht20.o drv-sht20.o
$(STRIP) -s test-sht20
clean:
rm -f test-sht20 test-sht20.o drv-sht20.o5 验证
1）编译测试代码，然后将其copy值NFS的挂载目录下，方便在板卡中运行该程序
2）在板卡中运行测试程序。在测试过程中，为了保证数据能有变化，可以对着sensor哈气，可以看见温度和湿度的值有明显的变化。说明驱动程序能够正常的工作。
6 逻辑分析仪查看波形
1）抓取一段i2c运行的波形图：
2） 详细波形图：
3）逻辑分析仪捕捉到的数据
