GPIO and sysfs Post: 303030530

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Top Forums UNIX for Advanced & Expert Users GPIO and sysfs Post 303030530 by Circuits on Tuesday 12th of February 2019 11:37:23 AM

02-12-2019

Registered User

GPIO and sysfs

I was recently working on a project where some gpio pins were being toggled from within the user space:

Code:

const char *const amplifierGPIO = "/sys/class/gpio/gpio107/value";

    void amplifierUnmute()
    {
      std::ofstream amp(amplifierGPIO);
      if (amp.is_open())
      {
        amp << "1";
        amp.close();
      }
    }

Now I am wondering how this works. For instance, is there some file where every pin which has been instantiated as a gpio pin is listed s/t the a user can access it like in the example above. Or does one have to go beyond instantiating the pin as gpio? For instance, lets say I build a pin as a gpio:

Code:

MX51_PIN_EIM_A24 = _MXC_BUILD_GPIO_PIN_MX51(1, 18, 1, 0xBC, 0x450),

Now how to access that pin inside the user space... it doesn't seem obvious to me how to go from instantiating a pin as a gpio pin to accessing it from the user space. It also seems foolish to believe that it is hard. I am going to start with this kernels Documentation/gpio.txt

Last edited by RudiC; 02-12-2019 at 01:07 PM..

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LEARN ABOUT CENTOS

struct_i2c_bus_recovery_info

STRUCT 
I2C_BUS_RECOV(9) 				      I2C and SMBus Subsystem					   STRUCT I2C_BUS_RECOV(9)

NAME

       struct_i2c_bus_recovery_info - I2C bus recovery information

SYNOPSIS

       struct i2c_bus_recovery_info {
	 int (* recover_bus) (struct i2c_adapter *);
	 int (* get_scl) (struct i2c_adapter *);
	 void (* set_scl) (struct i2c_adapter *, int val);
	 int (* get_sda) (struct i2c_adapter *);
	 void (* prepare_recovery) (struct i2c_bus_recovery_info *bri);
	 void (* unprepare_recovery) (struct i2c_bus_recovery_info *bri);
	 int scl_gpio;
	 int sda_gpio;
       };

MEMBERS

       recover_bus
	   Recover routine. Either pass driver's recover_bus routine, or i2c_generic_scl_recovery or i2c_generic_gpio_recovery.

       get_scl
	   This gets current value of SCL line. Mandatory for generic SCL recovery. Used internally for generic GPIO recovery.

       set_scl
	   This sets/clears SCL line. Mandatory for generic SCL recovery. Used internally for generic GPIO recovery.

       get_sda
	   This gets current value of SDA line. Optional for generic SCL recovery. Used internally, if sda_gpio is a valid GPIO, for generic GPIO
	   recovery.

       prepare_recovery
	   This will be called before starting recovery. Platform may configure padmux here for SDA/SCL line or something else they want.

       unprepare_recovery
	   This will be called after completing recovery. Platform may configure padmux here for SDA/SCL line or something else they want.

       scl_gpio
	   gpio number of the SCL line. Only required for GPIO recovery.

       sda_gpio
	   gpio number of the SDA line. Only required for GPIO recovery.

COPYRIGHT

Kernel Hackers Manual 3.10					     June 2014						   STRUCT I2C_BUS_RECOV(9)