通过wiringPi等library, 在user space 通过/dev/i2c来读写i2c设备的方案不在本文讨论了。
编译SENSORS_PCF8591 模块
在Default raspberryPi的内核中，pcf591模块是没有编译的。
查看drivershwmonMakefile
obj-$(CONFIG_HWMON) += hwmon.o
...
obj-$(CONFIG_SENSORS_PCF8591) += pcf8591.o
...
修改archarmconfigscm2709_defconfig, 增加一行 CONFIG_SENSORS_PCF8591=m
CONFIG_HWMON=m
...
CONFIG_SENSORS_PCF8591=m
执行
make mrproper
make modules将pcf8591.ko copy到raspberryPi板子
如果单独编译hwmon下的模块，
make modules SUBDIRS=drivers/hwmon/install module
pi@raspberrypi:/lib/modules/4.14.48-v7+/kernel/drivers/hwmon $ sudo insmod pcf8591.ko查看module是否install
pi@raspberrypi:/lib/modules/4.14.48-v7+/kernel/drivers/hwmon $ lsmod
Module Size Used by
pcf8591 16384 0
insmode 参数
The PCF8591 has 4 analog inputs programmable as single-ended or
differential inputs :
- mode 0 : four single ended inputs
Pins AIN0 to AIN3 are single ended inputs for channels 0 to 3
mode 1 : three differential inputs
Pins AIN3 is the common negative differential input
Pins AIN0 to AIN2 are positive differential inputs for channels 0 to 2mode 2 : single ended and differential mixed
Pins AIN0 and AIN1 are single ended inputs for channels 0 and 1
Pins AIN2 is the positive differential input for channel 3
Pins AIN3 is the negative differential input for channel 3mode 3 : two differential inputs
Pins AIN0 is the positive differential input for channel 0
Pins AIN1 is the negative differential input for channel 0
Pins AIN2 is the positive differential input for channel 1
Pins AIN3 is the negative differential input for channel 1
/* Insmod parameters */
I2C_CLIENT_INSMOD_1(pcf8591);
static int input_mode;
module_param(input_mode, int, 0);
MODULE_PARM_DESC(input_mode,
"Analog input mode:
"
" 0 = four single ended inputs
"
" 1 = three differential inputs
"
" 2 = single ended and differential mixed
"
" 3 = two differential inputs
");创建i2c device
查看i2c总线上的设备。 在使用中的0x68为RTC. 0x48为PCF8591
pi@raspberrypi:~ $ i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
70: -- -- -- -- -- -- 76 -- 创建设备
pi@raspberrypi:/sys/class/i2c-adapter/i2c-1 $ echo pcf8591 0x48 | sudo tee new_device
pcf8591 0x48
pi@raspberrypi:/sys/class/i2c-adapter/i2c-1 $ ls
1-0048 delete_device i2c-dev new_device power uevent
1-0068 device name of_node subsystem再次查看总线，可以看到0x48设置为UU， 表示在使用中
pi@raspberrypi:/sys/class/i2c-adapter/i2c-1 $ i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- UU -- -- -- -- -- -- --
70: -- -- -- -- -- -- 76 -- 查看
pi@raspberrypi:/sys/class/i2c-adapter/i2c-1/1-0048 $ ls
driver in0_input in2_input modalias out0_enable power uevent
hwmon in1_input in3_input name out0_output subsystem/sys Interface
The PCF8591 is plainly impossible to detect! Thus the driver won’t
even try. You have to explicitly instantiate the device at the
relevant address (in the interval [0x48..0x4f]) either through
platform data, or using the sysfs interface. See
Documentation/i2c/instantiating-devices for details.Directories are being created for each instantiated PCF8591:
/sys/bus/i2c/devices/<0>-<1>/ where <0> is the bus the chip is
connected to (e. g. i2c-0) and <1> the chip address ([48..4f])Inside these directories, there are such files: in0_input, in1_input,
in2_input, in3_input, out0_enable, out0_output, nameName contains chip name.
The in0_input, in1_input, in2_input and in3_input files are RO.
Reading gives the value of the corresponding channel. Depending on the
current analog inputs configuration, files in2_input and in3_input may
not exist. Values range from 0 to 255 for single ended inputs and -128
to +127 for differential inputs (8-bit ADC).The out0_enable file is RW. Reading gives “1” for analog output
enabled and “0” for analog output disabled. Writing accepts “0” and
“1” accordingly.The out0_output file is RW. Writing a number between 0 and 255 (8-bit
DAC), send the value to the digital-to-analog converter. Note that a
voltage will only appears on AOUT pin if aout0_enable equals 1.
Reading returns the last value written.