Staging: IIO: Initial documentation
This needs considerably more work, all comments / suggestions welcomed. Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Jonathan Cameron
Greg Kroah-Hartman
parent
930bae8667
commit
c57f1ba732
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IIO Device drivers
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This is not intended to provide a comprehensive guide to writing an
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IIO device driver. For further information see the drivers within the
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subsystem.
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The crucial structure for device drivers in iio is iio_dev.
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First allocate one using:
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struct iio_dev *indio_dev = iio_allocate_device();
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The fill in the following.
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indio_dev->dev.parent
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the struct device associated with the underlying hardware.
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indio_dev->num_interrupt_lines
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number of event triggering hardware lines the device has.
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indio_dev->event_attrs
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attributes used to enable / disable hardware events - note the
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attributes are embedded in iio_event_attr structures with an
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associated iio_event_handler which may or may note be shared.
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If num_interrupt_lines = 0, then no need to fill this in.
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indio_dev->attrs
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general attributes such as polled access to device channels.
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indio_dev->dev_data
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private device specific data.
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indio_dev->driver_module
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typically set to THIS_MODULE. Used to specify ownership of some
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iio created resources.
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indio_dev->modes
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whether direct access and / or ring buffer access is supported.
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Once these are set up, a call to iio_device_register(indio_dev),
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will register the device with the iio core.
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Worth noting here is that, if a ring buffer is to be used, it can be
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allocated prior to registering the device with the iio-core, but must
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be registered afterwards (otherwise the whole parentage of devices
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gets confused)
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On remove iio_device_unregister(indio_dev) will remove the device from
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the core, and iio_free_device will clean up.
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/* IIO - useful set of util functionality
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*
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* Copyright (c) 2008 Jonathan Cameron
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*/
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#define IIO_EVENT_CODE_RING_50_FULL 200
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#define IIO_EVENT_CODE_RING_75_FULL 201
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#define IIO_EVENT_CODE_RING_100_FULL 202
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struct iio_event_data {
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int id;
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__s64 timestamp;
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};
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inline char *find_ring_subelement(const char *directory, const char *subelement)
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{
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DIR *dp;
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const struct dirent *ent;
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int pos;
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char temp[100];
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char *returnstring;
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dp = opendir(directory);
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if (dp == NULL) {
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printf("could not directory: %s\n", directory);
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return NULL;
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}
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while (ent = readdir(dp), ent != NULL) {
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if (strcmp(ent->d_name, ".") != 0 &&
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strcmp(ent->d_name, "..") != 0) {
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if (strncmp(ent->d_name, subelement, strlen(subelement)) == 0) {
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int length = sprintf(temp, "%s%s%s", directory, ent->d_name, "/");
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returnstring = malloc(length+1);
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strncpy(returnstring, temp, length+1);
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return returnstring;
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}
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}
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}
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return 0;
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}
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char *find_type_by_name(const char *name, const char *type)
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{
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const char *iio_dir = "/sys/class/iio/";
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const struct dirent *ent;
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int cnt, pos, pos2;
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FILE *nameFile;
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DIR *dp;
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char thisname[100];
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char temp[100];
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char *returnstring = NULL;
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struct stat Stat;
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pos = sprintf(temp, "%s", iio_dir);
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dp = opendir(iio_dir);
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if (dp == NULL) {
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printf("No industrialio devices available");
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return NULL;
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}
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while (ent = readdir(dp), ent != NULL) {
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cnt++;
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/*reject . and .. */
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if (strcmp(ent->d_name, ".") != 0 &&
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strcmp(ent->d_name, "..") != 0) {
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/*make sure it isn't a trigger!*/
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if (strncmp(ent->d_name, type, strlen(type)) == 0) {
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/* build full path to new file */
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pos2 = pos + sprintf(temp + pos, "%s/", ent->d_name);
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sprintf(temp + pos2, "name");
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printf("search location %s\n", temp);
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nameFile = fopen(temp, "r");
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if (!nameFile) {
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sprintf(temp + pos2, "modalias", ent->d_name);
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nameFile = fopen(temp, "r");
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if (!nameFile) {
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printf("Failed to find a name for device\n");
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return NULL;
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}
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}
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fscanf(nameFile, "%s", thisname);
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if (strcmp(name, thisname) == 0) {
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returnstring = malloc(strlen(temp) + 1);
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sprintf(temp + pos2, "");
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strcpy(returnstring, temp);
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return returnstring;
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}
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fclose(nameFile);
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}
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}
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}
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}
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int write_sysfs_int(char *filename, char *basedir, int val)
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{
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int ret;
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FILE *sysfsfp;
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char temp[100];
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sprintf(temp, "%s%s", basedir, filename);
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sysfsfp = fopen(temp, "w");
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if (sysfsfp == NULL)
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return -1;
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fprintf(sysfsfp, "%d", val);
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fclose(sysfsfp);
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return 0;
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}
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/**
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* write_sysfs_string_and_verify() - string write, readback and verify
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* @filename: name of file to write to
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* @basedir: the sysfs directory in which the file is to be found
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* @val: the string to write
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**/
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int write_sysfs_string_and_verify(char *filename, char *basedir, char *val)
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{
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int ret;
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FILE *sysfsfp;
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char temp[100];
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sprintf(temp, "%s%s", basedir, filename);
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sysfsfp = fopen(temp, "w");
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if (sysfsfp == NULL)
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return -1;
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fprintf(sysfsfp, "%s", val);
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fclose(sysfsfp);
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sysfsfp = fopen(temp, "r");
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if (sysfsfp == NULL)
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return -1;
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fscanf(sysfsfp, "%s", temp);
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if (strcmp(temp, val) != 0) {
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printf("Possible failure in string write %s to %s%s \n",
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val,
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basedir,
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filename);
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return -1;
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}
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return 0;
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}
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int read_sysfs_posint(char *filename, char *basedir)
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{
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int ret;
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FILE *sysfsfp;
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char temp[100];
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sprintf(temp, "%s%s", basedir, filename);
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sysfsfp = fopen(temp, "r");
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if (sysfsfp == NULL)
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return -1;
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fscanf(sysfsfp, "%d\n", &ret);
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fclose(sysfsfp);
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return ret;
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}
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/* Industrialio test ring buffer with a lis3l02dq acceleromter
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*
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* Copyright (c) 2008 Jonathan Cameron
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*
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* Assumes suitable udev rules are used to create the dev nodes as named here.
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*/
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#include <dirent.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <errno.h>
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#include <stdint.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/dir.h>
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#include <linux/types.h>
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#include <dirent.h>
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#include "iio_util.h"
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static const char *ring_access = "/dev/iio/lis3l02dq_ring_access";
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static const char *ring_event = "/dev/iio/lis3l02dq_ring_event";
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static const char *device_name = "lis3l02dq";
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static const char *trigger_name = "lis3l02dq-dev0";
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static int NumVals = 3;
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static int scan_ts = 1;
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static int RingLength = 128;
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/*
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* Could get this from ring bps, but only after starting the ring
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* which is a bit late for it to be useful
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*/
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int size_from_scanmode(int numVals, int timestamp)
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{
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if (numVals && timestamp)
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return 16;
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else if (timestamp)
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return 8;
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else
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return numVals*2;
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}
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int main(int argc, char **argv)
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{
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int i, j, k, toread;
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FILE *fp_ev;
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int fp;
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char *data;
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size_t read_size;
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struct iio_event_data dat;
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char *BaseDirectoryName,
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*TriggerDirectoryName,
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*RingBufferDirectoryName;
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BaseDirectoryName = find_type_by_name(device_name, "device");
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if (BaseDirectoryName == NULL) {
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printf("Failed to find the %s \n", device_name);
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return -1;
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}
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TriggerDirectoryName = find_type_by_name(trigger_name, "trigger");
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if (TriggerDirectoryName == NULL) {
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printf("Failed to find the %s\n", trigger_name);
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return -1;
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}
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RingBufferDirectoryName = find_ring_subelement(BaseDirectoryName,
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"ring_buffer");
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if (RingBufferDirectoryName == NULL) {
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printf("Failed to find ring buffer\n");
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return -1;
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}
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if (write_sysfs_string_and_verify("trigger/current_trigger",
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BaseDirectoryName,
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(char *)trigger_name) < 0) {
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printf("Failed to write current_trigger file \n");
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return -1;
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}
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/* Setup ring buffer parameters */
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if (write_sysfs_int("length", RingBufferDirectoryName,
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RingLength) < 0) {
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printf("Failed to open the ring buffer length file \n");
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return -1;
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}
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/* Enable the ring buffer */
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if (write_sysfs_int("ring_enable", RingBufferDirectoryName, 1) < 0) {
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printf("Failed to open the ring buffer control file \n");
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return -1;
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};
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data = malloc(size_from_scanmode(NumVals, scan_ts)*RingLength);
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if (!data) {
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printf("Could not allocate space for usespace data store\n");
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return -1;
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}
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/* Attempt to open non blocking the access dev */
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fp = open(ring_access, O_RDONLY | O_NONBLOCK);
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if (fp == -1) { /*If it isn't there make the node */
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printf("Failed to open %s\n", ring_access);
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return -1;
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}
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/* Attempt to open the event access dev (blocking this time) */
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fp_ev = fopen(ring_event, "rb");
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if (fp_ev == NULL) {
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printf("Failed to open %s\n", ring_event);
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return -1;
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}
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/* Wait for events 10 times */
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for (j = 0; j < 10; j++) {
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read_size = fread(&dat, 1, sizeof(struct iio_event_data),
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fp_ev);
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switch (dat.id) {
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case IIO_EVENT_CODE_RING_100_FULL:
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toread = RingLength;
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break;
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case IIO_EVENT_CODE_RING_75_FULL:
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toread = RingLength*3/4;
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break;
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case IIO_EVENT_CODE_RING_50_FULL:
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toread = RingLength/2;
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break;
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default:
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printf("Unexpecteded event code\n");
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continue;
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}
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read_size = read(fp,
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data,
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toread*size_from_scanmode(NumVals, scan_ts));
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if (read_size == -EAGAIN) {
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printf("nothing available \n");
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continue;
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}
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for (i = 0;
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i < read_size/size_from_scanmode(NumVals, scan_ts);
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i++) {
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for (k = 0; k < NumVals; k++) {
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__s16 val = *(__s16 *)(&data[i*size_from_scanmode(NumVals, scan_ts)
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+ (k)*2]);
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printf("%05d ", val);
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}
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printf(" %lld\n",
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*(__s64 *)(&data[(i+1)*size_from_scanmode(NumVals, scan_ts)
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- sizeof(__s64)]));
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}
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}
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/* Stop the ring buffer */
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if (write_sysfs_int("ring_enable", RingBufferDirectoryName, 0) < 0) {
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printf("Failed to open the ring buffer control file \n");
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return -1;
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};
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/* Disconnect from the trigger - writing something that doesn't exist.*/
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write_sysfs_string_and_verify("trigger/current_trigger",
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BaseDirectoryName, "NULL");
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free(BaseDirectoryName);
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free(TriggerDirectoryName);
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free(RingBufferDirectoryName);
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free(data);
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return 0;
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}
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@ -0,0 +1,62 @@
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Overview of IIO
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The Industrial I/O subsytem is intended to provide support for devices
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that in some sense are analog to digital convertors (ADCs). As many
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actual devices combine some ADCs with digital to analog convertors
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(DACs) the intention is to add that functionality at a future date
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(hence the name).
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The aim is to fill the gap between the somewhat similar hwmon and
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input subsystems. Hwmon is very much directed at low sample rate
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sensors used in applications such as fan speed control and temperature
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measurement. Input is, as it's name suggests focused on input
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devices. In some cases there is considerable overlap between these and
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IIO.
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A typical device falling into this category would be connected via SPI
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or I2C.
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Functionality of IIO
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* Basic device registration and handling. This is very similar to
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hwmon with simple polled access to device channels via sysfs.
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* Event chrdevs. These are similar to input in that they provide a
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route to user space for hardware triggered events. Such events include
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threshold detectors, free-fall detectors and more complex action
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detection. They events themselves are currently very simple with
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merely an event code and a timestamp. Any data associated with the
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event must be accessed via polling. Note a given device may have one
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or more event channel. These events are turned on or off (if possible)
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via sysfs interfaces.
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* Hardware ring buffer support. Some recent sensors have included
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fifo / ring buffers on the sensor chip. These greatly reduce the load
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on the host CPU by buffering relatively large numbers of data samples
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based on an internal sampling clock. Examples include VTI SCA3000
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series and Analog Device ADXL345 accelerometers. Each ring buffer
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typically has an event chrdev (similar to the more general ones above)
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to pass on events such as buffer 50% full and an access chrdev via
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which the raw data it self may be read back.
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* Trigger and software ring buffer support. In many data analysis
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applications it it useful to be able to capture data based on some
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external signal (trigger). These triggers might be a data ready
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signal, a gpio line connected to some external system or an on
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processor periodic interrupt. A single trigger many initialize data
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capture or reading from a number of sensors. These triggers are
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used in iio to fill software ring buffers acting in a very similar
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fashion to the hardware buffers described above.
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Other documentation:
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userspace.txt - overview of ring buffer reading from userspace
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device.txt - elemennts of a typical device driver.
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trigger.txt - elements of a typical trigger driver.
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ring.txt - additional elements required for ring buffer support
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@ -0,0 +1,61 @@
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Ring buffer support within IIO
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This document is intended as a general overview of the functionality
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a ring buffer may supply and how it is specified within IIO. For more
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specific information on a given ring buffer implementation, see the
|
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comments in the source code. Note that the intention is to allow
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some drivers to specify ring buffers choice at probe or runtime, but
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for now the selection is hard coded within a given driver.
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A given ring buffer implementation typically embedded a struct
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iio_ring_buffer and it is a pointer to this that is provided to the
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IIO core. Access to the embedding structure is typically done via
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container_of functions.
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struct iio_ring_buffer contains 4 function pointers
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(preenable, postenable, predisable, postdisable).
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These are used to perform implementation specific steps on either side
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of the core changing it's current mode to indicate that the ring buffer
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is enabled or disabled (along with enabling triggering etc as appropriate).
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Also in struct iio_ring_buffer is a struct iio_ring_access_funcs.
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The function pointers within here are used to allow the core to handle
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as much ring buffer functionality as possible. Note almost all of these
|
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are optional.
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mark_in_use, unmark_in_use
|
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Basically indicate that not changes should be made to the ring
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buffer state that will effect the form of the data being captures
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(e.g. scan elements or length)
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store_to
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If possible, push data to ring buffer.
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read_last
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If possible get the most recent entry from the buffer (without removal).
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This provides polling like functionality whilst the ring buffering is in
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use without a separate read from the device.
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||||
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||||
rip_lots
|
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The primary ring buffer reading function. Note that it may well not return
|
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as much data as requested. The deadoffset is used to indicate that some
|
||||
initial data in the data array is not guaranteed to be valid.
|
||||
|
||||
mark_param_changed
|
||||
Used to indicate that something has changed. Used in conjunction with
|
||||
request_update
|
||||
If parameters have changed that require reinitialization or configuration of
|
||||
the ring buffer this will trigger it.
|
||||
|
||||
get_bpd, set_bpd
|
||||
Get/set the number of bytes for a given reading (single element, not sample set)
|
||||
The value of bps (bytes per set) is created from a combination of this and the
|
||||
enabled scan elements.
|
||||
|
||||
get_length / set_length
|
||||
Get/set the number of sample sets that may be held by the buffer.
|
||||
|
||||
is_enabled
|
||||
Query if ring buffer is in use
|
||||
enable
|
||||
Start the ring buffer.
|
||||
|
|
@ -0,0 +1,38 @@
|
|||
IIO trigger drivers.
|
||||
|
||||
Many triggers are provided by hardware that will also be registered as
|
||||
an IIO device. Whilst this can create device specific complexities
|
||||
such triggers are registered with the core in the same way as
|
||||
stand-alone triggers.
|
||||
|
||||
struct iio_trig *trig = iio_allocate_trigger();
|
||||
|
||||
allocates a trigger structure. The key elements to then fill in within
|
||||
a driver are:
|
||||
|
||||
trig->control_attrs
|
||||
Any sysfs attributes needed to control parameters of the trigger
|
||||
|
||||
trig->private_data
|
||||
Device specific private data.
|
||||
|
||||
trig->owner
|
||||
Typically set to THIS_MODULE. Used to ensure correct
|
||||
ownership of core allocated resources.
|
||||
|
||||
trig->name
|
||||
A unique name for the trigger.
|
||||
|
||||
When these have been set call:
|
||||
|
||||
iio_trigger_register(trig);
|
||||
|
||||
to register the trigger with the core, making it available to trigger
|
||||
consumers.
|
||||
|
||||
|
||||
Trigger Consumers
|
||||
|
||||
Currently triggers are only used for the filling of software ring
|
||||
buffers and as such any device supporting INDIO_RING_TRIGGERED has the
|
||||
consumer interface automatically created.
|
||||
|
|
@ -0,0 +1,60 @@
|
|||
Userspace access to IIO
|
||||
|
||||
Example, ST Microelectronics LIS3L02DQ accelerometer.
|
||||
|
||||
Typical sysfs entries (pruned for clarity)
|
||||
|
||||
/sys/class/iio
|
||||
device0 - iio_dev related elements
|
||||
name - driver specific identifier (here lis3l02dq)
|
||||
accel_x - polled (or from ring) raw readout of acceleration
|
||||
accel_x_gain - hardware gain (calibration)
|
||||
accel_x_offset - hardware offset (calibration)
|
||||
available_sampling_frequency
|
||||
|
||||
available_sampling_frequency - what options are there
|
||||
sampling_frequency - control of internal sampling frequency
|
||||
scan_elements - controls which channels will be stored in the ring buffer
|
||||
scan_en_accel_x
|
||||
scan_en_accel_y
|
||||
scan_en_timestamp
|
||||
device - link to underlying hardware device
|
||||
uevent - udev related element
|
||||
|
||||
thresh - unified threshold used for detection on all axis
|
||||
event_line0_sources - which events are enabled
|
||||
accel_x_high - enable x axis high threshold event
|
||||
accel_x_low - enable x axis low threshold event
|
||||
|
||||
event_line0 - event interface
|
||||
dev - major:minor for the chrdev (note major allocation dynamic)
|
||||
trigger - consumer attachement
|
||||
current_trigger - name based association with a trigger
|
||||
ring_buffer0 - ring buffer interface
|
||||
bps - byptes per sample (read only), dependant on scan element selection
|
||||
length - (rw) specificy length fo software ring buffer (typically ro in hw case)
|
||||
ring_enable - turn the ring on. If its the first to be enabled attached to this
|
||||
trigger will also enable the trigger.
|
||||
ring_access0
|
||||
dev - major:minor for ring buffer access chrdev
|
||||
ring_event_line0
|
||||
dev - major:minor for ring buffer event chrdev
|
||||
|
||||
trigger0 - data ready trigger elements
|
||||
name - unqiue name of trigger
|
||||
|
||||
Udev will create the following entries under /dev by default:
|
||||
|
||||
ring_access0 - ring access chrdev
|
||||
ring_event0 - ring event chrdev
|
||||
event_line0 - general event chrdev.
|
||||
|
||||
For the example code we assume the following rules have been used to ensure
|
||||
unique and consistent naming of these for the lis3l02dq in question:
|
||||
|
||||
KERNEL="ring_event_line*", ID="spi1.0", DRIVER="lis3l02dq", NAME="iio/lis3l02dq_ring_event"
|
||||
KERNEL="event_line*", ID="spi1.0", DRIVER="lis3l02dq", NAME="iio/lis3l02dq_event"
|
||||
KERNEL="ring_access*", ID="spi1.0", DRIVER="lis3l02dq", NAME="iio/lis3l02dq_ring_access"
|
||||
|
||||
The files, lis3l02dqbuffersimple.c and iio_util.h in this directory provide an example
|
||||
of how to use the ring buffer and event interfaces.
|
||||
Reference in New Issue