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// SPDX-License-Identifier: GPL-2.0-or-later
// SPDX-FileCopyrightText: 2023 Kent Gibson <warthog618@gmail.com>
/*
* Example of a bi-directional line requested as input and then switched
* to output.
*/
#include <errno.h>
#include <gpiod.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Request a line as input. */
static struct gpiod_line_request *request_input_line(const char *chip_path,
unsigned int offset,
const char *consumer)
{
struct gpiod_request_config *req_cfg = NULL;
struct gpiod_line_request *request = NULL;
struct gpiod_line_settings *settings;
struct gpiod_line_config *line_cfg;
struct gpiod_chip *chip;
int ret;
chip = gpiod_chip_open(chip_path);
if (!chip)
return NULL;
settings = gpiod_line_settings_new();
if (!settings)
goto close_chip;
gpiod_line_settings_set_direction(settings, GPIOD_LINE_DIRECTION_INPUT);
line_cfg = gpiod_line_config_new();
if (!line_cfg)
goto free_settings;
ret = gpiod_line_config_add_line_settings(line_cfg, &offset, 1,
settings);
if (ret)
goto free_line_config;
if (consumer) {
req_cfg = gpiod_request_config_new();
if (!req_cfg)
goto free_line_config;
gpiod_request_config_set_consumer(req_cfg, consumer);
}
request = gpiod_chip_request_lines(chip, req_cfg, line_cfg);
gpiod_request_config_free(req_cfg);
free_line_config:
gpiod_line_config_free(line_cfg);
free_settings:
gpiod_line_settings_free(settings);
close_chip:
gpiod_chip_close(chip);
return request;
}
static int reconfigure_as_output_line(struct gpiod_line_request *request,
unsigned int offset,
enum gpiod_line_value value)
{
struct gpiod_line_settings *settings;
struct gpiod_line_config *line_cfg;
int ret = -1;
settings = gpiod_line_settings_new();
if (!settings)
return -1;
gpiod_line_settings_set_direction(settings,
GPIOD_LINE_DIRECTION_OUTPUT);
gpiod_line_settings_set_output_value(settings, value);
line_cfg = gpiod_line_config_new();
if (!line_cfg)
goto free_settings;
ret = gpiod_line_config_add_line_settings(line_cfg, &offset, 1,
settings);
if (ret)
goto free_line_config;
ret = gpiod_line_request_reconfigure_lines(request, line_cfg);
free_line_config:
gpiod_line_config_free(line_cfg);
free_settings:
gpiod_line_settings_free(settings);
return ret;
}
static const char * value_str(enum gpiod_line_value value)
{
if (value == GPIOD_LINE_VALUE_ACTIVE)
return "Active";
else if (value == GPIOD_LINE_VALUE_INACTIVE) {
return "Inactive";
} else {
return "Unknown";
}
}
int main(void)
{
/* Example configuration - customize to suit your situation. */
static const char *const chip_path = "/dev/gpiochip0";
static const unsigned int line_offset = 5;
struct gpiod_line_request *request;
enum gpiod_line_value value;
int ret;
/* request the line initially as an input */
request = request_input_line(chip_path, line_offset,
"reconfigure-input-to-output");
if (!request) {
fprintf(stderr, "failed to request line: %s\n",
strerror(errno));
return EXIT_FAILURE;
}
/* read the current line value */
value = gpiod_line_request_get_value(request, line_offset);
printf("%d=%s (input)\n", line_offset, value_str(value));
/* switch the line to an output and drive it low */
ret = reconfigure_as_output_line(request, line_offset,
GPIOD_LINE_VALUE_INACTIVE);
/* report the current driven value */
value = gpiod_line_request_get_value(request, line_offset);
printf("%d=%s (output)\n", line_offset, value_str(value));
/* not strictly required here, but if the app wasn't exiting... */
gpiod_line_request_release(request);
return ret;
}
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