python smbus python smbus.SMBus

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mob6454cc79cd11 2021-12-16 11:19:45

文章标签 python 开发语言后端树莓派数据 文章分类 Python 后端开发

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：

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)

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)

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)

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)