在龙芯1c上使用RT-Thread统一标准的i2c接口

本文首先介绍几个常用的RTT统一的标准的I2C接口，然后以I2C接口的EEPROM芯片AT24C02为例，演示如何在龙芯1C上用RTT统一的I2C接口读取EEPROM芯片AT24C02。
在本文之前，已经写过几篇关于龙芯1C上，模拟I2C和硬件I2C，在裸机程序中和RTT中使用的文章，如下
【龙芯1c库】封装硬件I2C接口和使用示例
http://blog.csdn.net/caogos/article/details/77891546
在RT-Thread上使用龙芯1c库中的硬件I2C接口
http://blog.csdn.net/caogos/article/details/77892951
【龙芯1c库】封装模拟I2C接口和使用示例
http://blog.csdn.net/caogos/article/details/73089406
这几篇文章都是以“龙芯1C库”为背景的，而本文的不同之处在于重点讨论RTT统一标准的I2C接口，在龙芯1C上的移植和使用。

RTT统一的标准的I2C接口简介

初始化I2C

函数原型

int ls1c_i2c_init(void);

本函数的作用是，向RTT添加注册一个I2C总线。本函数为龙芯1C定制的函数，具体的实现细节放到后面移植部分再讨论。

使用示例

ls1c_i2c_init();

直接调用一下就行。
有的BSP里面是使用
INIT_DEVICE_EXPORT(ls1c_i2c_init);
的形式调用的，但在龙芯1C上没有这样采用。原因是每个人使用I2C时，可能使用不同的引脚。

Find设备

函数原型

/** * This function finds a device driver by specified name. * * @param name the device driver's name * * @return the registered device driver on successful, or RT_NULL on failure. */rt_device_t rt_device_find(const char *name)

函数rt_device_find()为RTT中通用的，find设备的函数。其它一些地方也可能会见到。入参为I2C总线的名字。I2C总线的名字在函数ls1c_i2c_init()中，调用函数rt_i2c_bit_add_bus()时注册的I2C总线名字。

使用示例

#define AT24C02_I2C_BUS_NAME                ("i2c2")struct rt_i2c_bus_device *at24c02_i2c_bus = RT_NULL;// find设备at24c02_i2c_bus = (struct rt_i2c_bus_device *)rt_device_find(AT24C02_I2C_BUS_NAME);if (RT_NULL == at24c02_i2c_bus){    rt_kprintf("[%s] no i2c device -- am2320!\n", __FUNCTION__);    return ;}

收发I2C信息

函数原型

rt_size_t rt_i2c_transfer(struct rt_i2c_bus_device *bus,                          struct rt_i2c_msg         msgs[],                          rt_uint32_t               num)

本函数是I2C收发的核心函数。收发都是调用本函数。具体是收，还是发，第二个入参中有个flags来控制。第一个入参为I2C总线（前面已经使用函数rt_device_find()得到的I2C总线），第三个入参为msg的个数，注意要与第二个参数中的len区别。
下面来详细看看第二个参数的结构体定义

struct rt_i2c_msg{    rt_uint16_t addr;    rt_uint16_t flags;    rt_uint16_t len;    rt_uint8_t  *buf;};

addr为I2C从机的地址，flags为此msg的一些标志，比如用来标记该msg是向从机读数据，还是写数据。len为此msg中收发数据的长度，buf为此msg收发的具体数据。
rt_i2c_msg为RTT为I2C封装的抽象概念。一次发送或接收，单独用一个msg来表示。
比如要读取AT24C02上某个地址的数据，先要把该数据的地址“写入”（发送）给AT24C02，然后再读取数据。这里面包含了两个msg，首先是一个写的msg，然后是一个读的msg。

使用示例

向AT24C02指定地址写入指定数据

/* * 在指定地址写入一个字节的数据 * @write_addr 地址 * @data 待写入的数据 */void at24c02_write_byte(unsigned char write_addr, unsigned char data){    struct rt_i2c_msg msg[1] = {0};    unsigned char buf[2] = {0};    buf[0] = write_addr;    buf[1] = data;        msg[0].addr    = at24c02_addr;    msg[0].flags   = RT_I2C_WR;    msg[0].buf     = buf;    msg[0].len     = 2;    rt_i2c_transfer(at24c02_i2c_bus, msg, 1);    return ;}

从AT24C02指定地址读出数据

/* * 从指定地址读出一个字节 * @read_addr 地址 */unsigned char at24c02_read_byte(unsigned char read_addr){    struct rt_i2c_msg msgs[2];    unsigned char data = 0;    msgs[0].addr    = at24c02_addr;    msgs[0].flags   = RT_I2C_WR;    msgs[0].buf     = &read_addr;    msgs[0].len     = 1;    msgs[1].addr    = at24c02_addr;    msgs[1].flags   = RT_I2C_RD;    msgs[1].buf     = &data;    msgs[1].len     = 1;    rt_i2c_transfer(at24c02_i2c_bus, msgs, 2);    return data;}

综合应用示例——在龙芯1C上接I2C接口的EEPROM芯片AT24C02

测试的思路是，在at24c02内，地址为1的地方保存复位次数。每次上电后，先读取当前次数，并打印，然后加一，并保存到at24c02中。为了验证保存正确，在读取一次，并将读取的结果打印出来。

实物图

电路连接为
AT24C02                     龙芯1c
VCC   ------------------- 3.3V
GND  ------------------- GND
SCL   ------------------- GPIO57
SDA   ------------------ GPIO56

串口打印

测试源码清单

在前面介绍函数rt_i2c_transfer（）时，已经把读写eeprom的函数介绍了，读写eeprom是本测试用例中的核心代码，这里就直接把完整的测试代码贴出来（I2C移植的部分代码稍后再讨论）。

application.c

bsp\ls1cdev\applications\application.c

/* * File      : application.c * This file is part of RT-Thread RTOS * COPYRIGHT (C) 2006-2012, RT-Thread Develop Team * * The license and distribution terms for this file may be * found in the file LICENSE in this distribution or at * http://www.rt-thread.org/license/LICENSE * * Change Logs: * Date                Author         Notes * 2010-06-25          Bernard        first version * 2011-08-08          lgnq           modified for Loongson LS1B * 2015-07-06          chinesebear    modified for Loongson LS1C */#include <rtthread.h>#include "net/synopGMAC.h"#include <lwip/api.h>#include <drivers/i2c.h>#include "../drivers/drv_i2c.h"// 测试用的线程  #define THREAD_TEST_PRIORITY                    (25)  #define THREAD_TEST_STACK_SIZE                  (4*1024)        // 4k  #define THREAD_TEST_TIMESLICE                   (10)  #define AT24C02_I2C_BUS_NAME                ("i2c2")        // 注意与i2c bus初始化函数中的bus name保持一致struct rt_i2c_bus_device *at24c02_i2c_bus = RT_NULL;int at24c02_addr = 0xA0 >> 1;               // 地址前7位  struct rt_thread thread_test;  ALIGN(8) rt_uint8_t thread_test_stack[THREAD_TEST_STACK_SIZE];  /* * 从指定地址读出一个字节 * @read_addr 地址 */unsigned char at24c02_read_byte(unsigned char read_addr){    struct rt_i2c_msg msgs[2];    unsigned char data = 0;    msgs[0].addr    = at24c02_addr;    msgs[0].flags   = RT_I2C_WR;    msgs[0].buf     = &read_addr;    msgs[0].len     = 1;    msgs[1].addr    = at24c02_addr;    msgs[1].flags   = RT_I2C_RD;    msgs[1].buf     = &data;    msgs[1].len     = 1;    rt_i2c_transfer(at24c02_i2c_bus, msgs, 2);    return data;}/* * 在指定地址写入一个字节的数据 * @write_addr 地址 * @data 待写入的数据 */void at24c02_write_byte(unsigned char write_addr, unsigned char data){    struct rt_i2c_msg msg[1] = {0};    unsigned char buf[2] = {0};    buf[0] = write_addr;    buf[1] = data;        msg[0].addr    = at24c02_addr;    msg[0].flags   = RT_I2C_WR;    msg[0].buf     = buf;    msg[0].len     = 2;    rt_i2c_transfer(at24c02_i2c_bus, msg, 1);    return ;}// 测试用的线程的入口  void thread_test_entry(void *parameter)  {    unsigned char read_addr = 1;    // 地址    unsigned char count = 0;        // 用于计数的变量    // 初始化(添加i2c总线--i2c2)    ls1c_i2c_init();    // find设备    at24c02_i2c_bus = (struct rt_i2c_bus_device *)rt_device_find(AT24C02_I2C_BUS_NAME);    if (RT_NULL == at24c02_i2c_bus)    {        rt_kprintf("[%s] no i2c device -- am2320!\n", __FUNCTION__);        return ;    }    // 读    count = at24c02_read_byte(read_addr);    rt_kprintf("[%s] last's count=%u\n", __FUNCTION__, count);    // 加一，然后写    count++;    at24c02_write_byte(read_addr, count);    rt_thread_delay(6);     // 一定要延时5ms以上    // 读    count = at24c02_read_byte(read_addr);    rt_kprintf("[%s] current count=%d\n", __FUNCTION__, count);        while (1)      {        // 间隔3s        rt_thread_delay(3 * RT_TICK_PER_SECOND);      }  }  void rt_init_thread_entry(void *parameter){/* initialization RT-Thread Components */rt_components_init();    // 网口EMAC初始化rt_hw_eth_init();}int rt_application_init(void){rt_thread_t tid;    rt_err_t result;/* create initialization thread */tid = rt_thread_create("init",rt_init_thread_entry, RT_NULL,4096, RT_THREAD_PRIORITY_MAX/3, 20);if (tid != RT_NULL)rt_thread_startup(tid);      // 初始化测试用的线程      result = rt_thread_init(&thread_test,                               "thread_test",                              thread_test_entry,                              RT_NULL,                              &thread_test_stack[0],                              sizeof(thread_test_stack),                              THREAD_TEST_PRIORITY,                              THREAD_TEST_TIMESLICE);      if (RT_EOK == result)      {          rt_thread_startup(&thread_test);      }      else      {          return -1;      }  return 0;}

把RTT统一的标准的I2C接口移植到龙芯1C上

移植要点

RTT支持硬件I2C和模拟I2C，这里使用的是模拟I2C。大家都知道，其实模拟I2C本身就不难，而RTT又把其中一些非硬件相关的，通用的部分提出来了，那么留给我们移植的工作量就更少了。简单来说就只需要实现读取和设置scl和sda的函数就可以了。对应代码为

static const struct rt_i2c_bit_ops bit_ops = {    .data       = RT_NULL,    .set_sda    = ls1c_set_sda,    .set_scl    = ls1c_set_scl,    .get_sda    = ls1c_get_sda,    .get_scl    = ls1c_get_scl,    .udelay     = ls1c_udelay,    .delay_us   = 20,       // 此值为周期(us)    .timeout    = 10,       // 单位为tick};

这个结构体中的函数都实现好后，然后调用函数rt_i2c_bit_add_bus（）把bit_ops注册一下就可以了。具体代码为

int ls1c_i2c_init(void){    static struct rt_i2c_bus_device bus = {0};    bus.priv = (void *)&bit_ops;    ls1c_i2c_gpio_init();    rt_i2c_bit_add_bus(&bus, "i2c2");    return RT_EOK;}

这是一个I2C的驱动，假设想再增加一个呢？道理类似，依葫芦画瓢，把scl和sda的引脚改一下，把I2C总线的名字改一下，基本就可以了。
最后在特别说明一下，目前龙芯的gpio没有开漏输出模式，所以在读取sda值的时候需要先设为输入模式。如下

static rt_int32_t ls1c_get_sda(void *data){#ifdef LS1C_SET_GPIO_MODE    gpio_init(LS1C_I2C_SDA, gpio_mode_input);    ls1c_udelay(5);#endif    return gpio_get(LS1C_I2C_SDA);}static void ls1c_set_sda(void *data, rt_int32_t state){#ifdef LS1C_SET_GPIO_MODE    gpio_init(LS1C_I2C_SDA, gpio_mode_output);    ls1c_udelay(5);#endif    gpio_set(LS1C_I2C_SDA, state);    return ;}

其中，对GPIO的操作还是使用的龙芯1C库中的gpio函数（bsp\ls1cdev\libraries\ls1c_gpio.h中）。

源码清单

drv_i2c.c

bsp\ls1cdev\drivers\drv_i2c.c

/* * File      : drv_i2c.c * This file is part of RT-Thread RTOS * COPYRIGHT (C) 2006 - 2012, RT-Thread Development Team * *  This program is free software; you can redistribute it and/or modify *  it under the terms of the GNU General Public License as published by *  the Free Software Foundation; either version 2 of the License, or *  (at your option) any later version. * *  This program is distributed in the hope that it will be useful, *  but WITHOUT ANY WARRANTY; without even the implied warranty of *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the *  GNU General Public License for more details. * *  You should have received a copy of the GNU General Public License along *  with this program; if not, write to the Free Software Foundation, Inc., *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. * * Change Logs: * Date           Author       Notes * 2017-11-14     勤为本       first version */#include <rtthread.h>#include <drivers/i2c.h>#include <drivers/i2c-bit-ops.h>#include "drv_i2c.h"#include "../libraries/ls1c_gpio.h"#include "../libraries/ls1c_delay.h"#define LS1C_I2C_SCL                (57)    // gpio57#define LS1C_I2C_SDA                (56)    // gpio56#define LS1C_SET_GPIO_MODEstatic void ls1c_i2c_gpio_init(void){    gpio_init(LS1C_I2C_SCL, gpio_mode_output);    gpio_set(LS1C_I2C_SCL, gpio_level_high);    gpio_init(LS1C_I2C_SDA, gpio_mode_output);    gpio_set(LS1C_I2C_SDA, gpio_level_high);    return ;}static void ls1c_udelay(rt_uint32_t us){    delay_us((int)us);}static void ls1c_set_sda(void *data, rt_int32_t state){#ifdef LS1C_SET_GPIO_MODE    gpio_init(LS1C_I2C_SDA, gpio_mode_output);    ls1c_udelay(5);#endif    gpio_set(LS1C_I2C_SDA, state);    return ;}static void ls1c_set_scl(void *data, rt_int32_t state){#ifdef LS1C_SET_GPIO_MODE    gpio_init(LS1C_I2C_SCL, gpio_mode_output);    ls1c_udelay(5);#endif    gpio_set(LS1C_I2C_SCL, state);    return ;}static rt_int32_t ls1c_get_sda(void *data){#ifdef LS1C_SET_GPIO_MODE    gpio_init(LS1C_I2C_SDA, gpio_mode_input);    ls1c_udelay(5);#endif    return gpio_get(LS1C_I2C_SDA);}static rt_int32_t ls1c_get_scl(void *data){#ifdef LS1C_SET_GPIO_MODE    gpio_init(LS1C_I2C_SCL, gpio_mode_input);    ls1c_udelay(5);#endif    return gpio_get(LS1C_I2C_SCL);}static const struct rt_i2c_bit_ops bit_ops = {    .data       = RT_NULL,    .set_sda    = ls1c_set_sda,    .set_scl    = ls1c_set_scl,    .get_sda    = ls1c_get_sda,    .get_scl    = ls1c_get_scl,    .udelay     = ls1c_udelay,    .delay_us   = 20,       // 此值为周期(us)    .timeout    = 10,       // 单位为tick};int ls1c_i2c_init(void){    static struct rt_i2c_bus_device bus = {0};    bus.priv = (void *)&bit_ops;    ls1c_i2c_gpio_init();    rt_i2c_bit_add_bus(&bus, "i2c2");    return RT_EOK;}

感谢阅读！