[Python知识库]Python Smbus库简介

背景

手头有个树莓派，又有个I2C通信的模块，因此想要用树莓派调一下这个模块，于是找了下树莓派控制模块的文章，发现都是从smbus的read byte封装的，可是按照I2C协议一次肯定可以读多个数据，于是想找库函数文档看下，发现Py官网文档上smbus库没有函数描述，但找到了语法与其相同的smbus2库, 于是记录下库函数用法。不过找到了smbus的源码， 源码中有函数接口。

结果

smbus支持的函数列表：

static PyMethodDef SMBus_methods[] = {
	{"open", (PyCFunction)SMBus_open, METH_VARARGS | METH_KEYWORDS,
		SMBus_open_doc},
	{"close", (PyCFunction)SMBus_close, METH_NOARGS,
		SMBus_close_doc},
	{"write_quick", (PyCFunction)SMBus_write_quick, METH_VARARGS,
		SMBus_write_quick_doc},
	{"read_byte", (PyCFunction)SMBus_read_byte, METH_VARARGS,
		SMBus_read_byte_doc},
	{"write_byte", (PyCFunction)SMBus_write_byte, METH_VARARGS,
		SMBus_write_byte_doc},
	{"read_byte_data", (PyCFunction)SMBus_read_byte_data, METH_VARARGS,
		SMBus_read_byte_data_doc},
	{"write_byte_data", (PyCFunction)SMBus_write_byte_data, METH_VARARGS,
		SMBus_write_byte_data_doc},
	{"read_word_data", (PyCFunction)SMBus_read_word_data, METH_VARARGS,
		SMBus_read_word_data_doc},
	{"write_word_data", (PyCFunction)SMBus_write_word_data, METH_VARARGS,
		SMBus_write_word_data_doc},
	{"process_call", (PyCFunction)SMBus_process_call, METH_VARARGS,
		SMBus_process_call_doc},
	{"read_block_data", (PyCFunction)SMBus_read_block_data, METH_VARARGS,
		SMBus_read_block_data_doc},
	{"write_block_data", (PyCFunction)SMBus_write_block_data, METH_VARARGS,
		SMBus_write_block_data_doc},
	{"block_process_call", (PyCFunction)SMBus_block_process_call,
		METH_VARARGS, SMBus_block_process_call_doc},
	{"read_i2c_block_data", (PyCFunction)SMBus_read_i2c_block_data,
		METH_VARARGS, SMBus_read_i2c_block_data_doc},
	{"write_i2c_block_data", (PyCFunction)SMBus_write_i2c_block_data,
		METH_VARARGS, SMBus_write_i2c_block_data_doc},
	{NULL},
};

该函数库是C库，smbus2是纯python库；

用法

常用函数用法介绍及示例：

1. 读单字节；

   from smbus import SMBus
   
   # Open i2c bus 1 and read one byte from address 80, offset 0
   bus = SMBus(1)
   b = bus.read_byte_data(80, 0)
   print(b)
   bus.close()
   

   上面的代码如果句柄忘记了关闭，存在安全性风险， 可以使用with语句进行自动释放资源：

   from smbus import SMBus
   
   with SMBus(1) as bus:
       b = bus.read_byte_data(80, 0)
       print(b)
   

   更进一步可以打开包错误校验（Packet Error Checking， PEC）：

   from smbus import SMBus
   
   with SMBus(1) as bus:
       bus.pec = 1  # Enable PEC
       b = bus.read_byte_data(80, 0)
       print(b)
   

2. 读取一块数据

   from smbus import SMBus
   
   with SMBus(1) as bus:
       # Read a block of 16 bytes from address 80, offset 0
       block = bus.read_i2c_block_data(80, 0, 16)
       # Returned value is a list of 16 bytes
       print(block)
   

   一次最多可以读取32字节；
3. 写入一个字节

   from smbus import SMBus
   
   with SMBus(1) as bus:
       # Write a byte to address 80, offset 0
       data = 45
       bus.write_byte_data(80, 0, data)
   

4. 写入一块数据

   from smbus import SMBus
   
   with SMBus(1) as bus:
       # Write a block of 8 bytes to address 80 from offset 0
       data = [1, 2, 3, 4, 5, 6, 7, 8]
       bus.write_i2c_block_data(80, 0, data)
   

   一次最多写入32字节；

参考文档

1. smbus2-project description
2. smbus源码；
3. 树莓派（Raspberry Pi）python smbus 函数说明