4. I2C 使用¶
4.1. 简介¶
ITX-3568Q开发板上有 6 个片上 I2C 控制器,各个 I2C 的使用情况如下表:
Port | Pin name | Device |
---|---|---|
I2C0 | GPIO0_B1/I2C0_SCL GPIO0_B2/I2C0_SDA |
RK809 |
I2C1 | GPIO0_B3/I2C1_SCL GPIO0_B4/I2C1_SDA |
TP/HYM8563 |
I2C2_M0 | GPIO0_B5/I2C2_SCL_M0 GPIO0_B6/I2C2_SDA_M0 |
复用为其他功能 |
I2C2_M1 | GPIO4_B5/I2C2_SCL_M1 GPIO4_B4/I2C2_SDA_M1 |
VGA |
I2C3_M0 | GPIO1_A1/I2C3_SCL_M0 GPIO1_A0/I2C3_SDA_M0 |
复用为其他功能 |
I2C3_M1 | GPIO3_B5/I2C3_SCL_M1 GPIO3_B6/I2C3_SDA_M1 |
复用为其他功能 |
I2C4_M0 | GPIO4_B3/I2C4_SCL_M0 GPIO4_B2/I2C4_SDA_M0 |
camera |
I2C4_M1 | GPIO2_B2/I2C4_SCL_M1 GPIO2_B1/I2C4_SDA_M1 |
复用为其他功能 |
I2C5_M0 | GPIO3_B3/I2C5_SCL_M0 GPIO3_B4/I2C5_SDA_M0 |
复用为其他功能 |
I2C5_M1 | GPIO4_C7/I2C5_SCL_M1 GPIO4_D0/I2C5_SDA_M1 |
复用为其他功能 |
本文主要描述如何在该开发板上配置 I2C。
配置 I2C 可分为两大步骤:
定义和注册 I2C 设备
定义和注册 I2C 驱动
下面以配置 GSL3680 为例。
4.2. 定义和注册 I2C 设备¶
在注册 I2C 设备时,需要结构体 i2c_client
来描述 I2C 设备。然而在标准 Linux 中,用户只需要提供相应的 I2C 设备信息,Linux 就会根据所提供的信息构造 i2c_client
结构体。
用户所提供的 I2C 设备信息以节点的形式写到 DTS 文件中,如下所示:
kernel/arch/arm64/boot/dts/rockchip/rk3568-firefly-itx-3568q-lvds101_HSX101H40C.dts
&i2c1 {
status = "okay";
clock-frequency = <100000>;
//i2c-scl-rising-time-ns = <800>;
//i2c-scl-falling-time-ns = <100>;
gslx680: gslx680@41 {
status = "okay";
compatible = "gslX680";
reg = <0x41>;
screen_max_x = <800>;
screen_max_y = <1280>;
touch-gpio = <&gpio0 RK_PC7 IRQ_TYPE_LEVEL_LOW>;
reset-gpio = <&pca9555 PCA_IO1_0 GPIO_ACTIVE_HIGH>;
flip-x = <1>;
flip-y = <0>;
swap-xy = <0>;
gsl,fw = <1>;
};
};
...
4.3. 定义和注册 I2C 驱动¶
4.3.1. 定义 I2C 驱动¶
在定义 I2C 驱动之前,用户首先要定义变量 of_device_id
和 i2c_device_id
。
of_device_id
用于在驱动中调用 DTS 文件中定义的设备信息,其定义如下所示:
static struct of_device_id gsl_ts_ids[] = {
{.compatible = "gslX680"},
{}
};
定义变量 i2c_device_id
:
static const struct i2c_device_id gsl_ts_id[] = {
{GSLX680_I2C_NAME, 0},
{}
};
MODULE_DEVICE_TABLE(i2c, gsl_ts_id);
i2c_driver
如下所示:
static struct i2c_driver gsl_ts_driver = {
.driver = { .name = GSLX680_I2C_NAME,
.owner = THIS_MODULE,
.of_match_table = of_match_ptr(gsl_ts_ids),
},
#ifndef CONFIG_HAS_EARLYSUSPEND
//.suspend = gsl_ts_suspend,
//.resume = gsl_ts_resume,
#endif
.probe = gsl_ts_probe,
.remove = gsl_ts_remove,
.id_table = gsl_ts_id,
};
注:变量 id_table
指示该驱动所支持的设备。
4.3.2. 注册 I2C 驱动¶
使用 i2c_add_driver
函数注册 I2C 驱动。
i2c_add_driver(&gsl_ts_driver);
在调用 i2c_add_driver
注册 I2C 驱动时,会遍历 I2C 设备,如果该驱动支持所遍历到的设备,则会调用该驱动的 probe
函数。
4.3.3. 通过 I2C 收发数据¶
在注册好 I2C 驱动后,即可进行 I2C 通讯。
向从机发送信息:
int i2c_master_send(const struct i2c_client *client, const char *buf, int count)
{
int ret;
struct i2c_adapter *adap = client->adapter;
struct i2c_msg msg;
msg.addr = client->addr;
msg.flags = client->flags & I2C_M_TEN;
msg.len = count;
msg.buf = (char *)buf;
ret = i2c_transfer(adap, &msg, 1);
/*
* If everything went ok (i.e. 1 msg transmitted), return #bytes
* transmitted, else error code.
*/
return (ret == 1) ? count : ret;
}
向从机读取信息:
int i2c_master_recv(const struct i2c_client *client, char *buf, int count)
{
struct i2c_adapter *adap = client->adapter;
struct i2c_msg msg;
int ret;
msg.addr = client->addr;
msg.flags = client->flags & I2C_M_TEN;
msg.flags |= I2C_M_RD;
msg.len = count;
msg.buf = buf;
ret = i2c_transfer(adap, &msg, 1);
/*
* If everything went ok (i.e. 1 msg received), return #bytes received,
* else error code.
*/
return (ret == 1) ? count : ret;
}
EXPORT_SYMBOL(i2c_master_recv);
4.4. FAQs¶
4.4.1. Q1: 通信失败,出现这种 log: “timeout, ipd: 0x00, state: 1” 该如何调试?¶
A1: 请检查硬件上拉是否给电。
4.4.2. Q2: 调用 i2c_transfer 返回值为 -6?¶
A2: 返回值为 -6 表示为 NACK 错误,即对方设备无应答响应,这种情况一般为外设的问题,常见的有以下几种情况:
I2C 地址错误,解决方法是测量 I2C 波形,确认是否 I2C 设备地址错误;
I2C slave 设备不处于正常工作状态,比如未给电,错误的上电时序等;
时序不符合 I2C slave 设备所要求也会产生 Nack 信号。
4.4.3. Q3: 当外设对于读时序要求中间是 stop 信号不是 repeat start 信号的时候,该如何处理?¶
A3: 这时需要调用两次 i2c_transfer, I2C read 拆分成两次,修改如下:
static int i2c_read_bytes(struct i2c_client *client, u8 cmd, u8 *data, u8 data_len) {
struct i2c_msg msgs[2];
int ret;
u8 *buffer;
buffer = kzalloc(data_len, GFP_KERNEL);
if (!buffer)
return -ENOMEM;;
msgs[0].addr = client->addr;
msgs[0].flags = client->flags;
msgs[0].len = 1;
msgs[0].buf = &cmd;
ret = i2c_transfer(client->adapter, msgs, 1);
if (ret < 0) {
dev_err(&client->adapter->dev, "i2c read failed\n");
kfree(buffer);
return ret;
}
msgs[1].addr = client->addr;
msgs[1].flags = client->flags | I2C_M_RD;
msgs[1].len = data_len;
msgs[1].buf = buffer;
ret = i2c_transfer(client->adapter, &msgs[1], 1);
if (ret < 0)
dev_err(&client->adapter->dev, "i2c read failed\n");
else
memcpy(data, buffer, data_len);
kfree(buffer);
return ret;
}