Advantech RSB-4210 Evaluation Kit Manual de usuario descargar pdf (Pagina 64)

RSB-4210 User Manual 56

"edge" reads as either "none", "rising", "falling", or "both". Write these strings

to select the signal edge(s) that will make poll(2) on the "value" file

return.

This file exists only if the pin can be configured as aninterrupt generat-

ing input pin.

"active_low" reads as either 0 (false) or 1 (true). Write any nonzero value to invert

the value attribute both for reading and writing. Existing and subse-

quent poll(2) support configuration via the edge attribute for "rising"

and "falling" edges will follow this setting.

GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the

controller implementing GPIOs starting at #42) and have the following

read-only attributes:

/sys/class/gpio/gpiochipN/

"base" ... same as N, the first GPIO managed by the chip

"label" ... provided for diagnostics (not always unique)

"ngpio" ... how many GPIOs this manges (N to N + ngpio - 1)

Board documentation should in most cases cover what GPIOs are used for what pur-

poses. However, those numbers are not always stable; GPIOs on a daughtercard

might be different depending on the base board being used, or other cards in the

stack. In such cases, you may need to use the gpiochip nodes (possibly in conjunc-

tion with schematics) to determine the correct GPIO number to use for a given signal.

Exporting from Kernel code

Kernel code can explicitly manage exports of GPIOs which have already been

requested using gpio_request():

/* export the GPIO to userspace */

int gpio_export(unsigned gpio, bool

direction_may_change);

/* reverse gpio_export() */

void gpio_unexport();

/* create a sysfs link to an exported GPIO node */

int gpio_export_link(struct device *dev, const char

*name, unsigned gpio)

/* change the polarity of a GPIO node in sysfs */

int gpio_sysfs_set_active_low(unsigned gpio, int value);

After a kernel driver requests a GPIO, it may only be made available in the sysfs

interface by gpio_export(). The driver can control whether the signal direction may

change. This helps drivers prevent userspace code from accidentally clobbering

important system state.

(More detail please reference "source/linux-2.6.35.3/Documentation/ gpio.txt")

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Advantech RSB-4210 Evaluation Kit Manual de usuario Pagina 64