Analog IO with C/C++ code

[Justin Reina]

Hi guys,
 Alright I submit, I give in and come to you and now ask for help. I am amiss as to how this has been so magically elusive, but it has!

Question

How can you do Analog Input and Analog Output of discrete values from either a terminal or C/C++ code?

Specific Hardware

BeagleBone Black Rev. C, Debian Jessie 8.4

Research

I have found discussions claiming AIO support for the BBB, but these both were greater than 3 years old and referenced non-existant directories in the file system!

I have also found a plethora of Bonescript solutions

I am still amiss as to how this is not BBB-101 and the first example code you encounter! Please let me know where to look for reference and example, and get this in action!

Thanks :)
  Justin Reina

[evilwulfie]

analog in
http://www.embeddedhobbyist.com/2015/10/beaglebone-black-adc/

there is no analog out unless you hook up a DAC

--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/ac5a6fc8-042d-41d0-9380-31ad615a8109%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[John Syne]

Well, that example shows the incorrect way to use IIO if you want to continuously collect samples from the ADC. The correct way to use IIO is to read from

/dev/iio:device0

You start by selecting which channels you want to sample. For example, if you want to enable the first 2 channels

echo 1 > /sys/bus/iio/devices/iio:device0/scan_elements/in_voltage0_en
echo 1 > /sys/bus/iio/devices/iio:device0/scan_elements/in_voltage1_en

Then you enable the buffer capture

echo 1 > /sys/bus/iio/devices/iio:device0/buffer/enable

Here is an example app from the IIO framework. If you search Google for "generic_buffer iio” you will find this app, but I have included some fixes to make it work with the latest IIO.

/* Industrialio buffer test code.
*
* Copyright (c) 2008 Jonathan Cameron
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
*
* This program is primarily intended as an example application.
* Reads the current buffer setup from sysfs and starts a short capture
* from the specified device, pretty printing the result after appropriate
* conversion.
*
* Command line parameters
* generic_buffer -n <device_name> -t <trigger_name>
* If trigger name is not specified the program assumes you want a dataready
* trigger associated with the device and goes looking for it.
*
*/

#include <unistd.h>
#include <stdlib.h>
#include <dirent.h>
#include <fcntl.h>
#include <stdio.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/dir.h>
#include <linux/types.h>
#include <string.h>
#include <poll.h>
#include <endian.h>
#include <getopt.h>
#include <inttypes.h>
#include "iio_utils.h"

/**
* size_from_channelarray() - calculate the storage size of a scan
* @channels: the channel info array
* @num_channels: number of channels
*
* Has the side effect of filling the channels[i].location values used
* in processing the buffer output.
**/
int size_from_channelarray(struct iio_channel_info *channels, int num_channels)
{
int bytes = 0;
int i = 0;

while (i < num_channels) {
if (bytes % channels[i].bytes == 0)
channels[i].location = bytes;
else
channels[i].location = bytes - bytes % channels[i].bytes
+ channels[i].bytes;

bytes = channels[i].location + channels[i].bytes;
i++;
}

return bytes;
}

void print1byte(uint8_t input, struct iio_channel_info *info)
{
/*
* Shift before conversion to avoid sign extension
* of left aligned data
*/
input >>= info->shift;
input &= info->mask;
if (info->is_signed) {
int8_t val = (int8_t)(input << (8 - info->bits_used)) >>
(8 - info->bits_used);
printf("%05f ", ((float)val + info->offset) * info->scale);
} else {
printf("%05f ", ((float)input + info->offset) * info->scale);
}
}

void print2byte(uint16_t input, struct iio_channel_info *info)
{
/* First swap if incorrect endian */
if (info->be)
input = be16toh(input);
else
input = le16toh(input);

/*
* Shift before conversion to avoid sign extension
* of left aligned data
*/
input >>= info->shift;
input &= info->mask;
if (info->is_signed) {
int16_t val = (int16_t)(input << (16 - info->bits_used)) >>
(16 - info->bits_used);
printf("%05f ", ((float)val + info->offset) * info->scale);
} else {
printf("%05f ", ((float)input + info->offset) * info->scale);
}
}

void print4byte(uint32_t input, struct iio_channel_info *info)
{
/* First swap if incorrect endian */
if (info->be)
input = be32toh(input);
else
input = le32toh(input);

/*
* Shift before conversion to avoid sign extension
* of left aligned data
*/
input >>= info->shift;
input &= info->mask;
if (info->is_signed) {
int32_t val = (int32_t)(input << (32 - info->bits_used)) >>
(32 - info->bits_used);
printf("%05f ", ((float)val + info->offset) * info->scale);
} else {
printf("%05f ", ((float)input + info->offset) * info->scale);
}
}

void print8byte(uint64_t input, struct iio_channel_info *info)
{
/* First swap if incorrect endian */
if (info->be)
input = be64toh(input);
else
input = le64toh(input);

/*
* Shift before conversion to avoid sign extension
* of left aligned data
*/
input >>= info->shift;
input &= info->mask;
if (info->is_signed) {
int64_t val = (int64_t)(input << (64 - info->bits_used)) >>
(64 - info->bits_used);
/* special case for timestamp */
if (info->scale == 1.0f && info->offset == 0.0f)
printf("%" PRId64 " ", val);
else
printf("%05f ",
((float)val + info->offset) * info->scale);
} else {
printf("%05f ", ((float)input + info->offset) * info->scale);
}
}

/**
* process_scan() - print out the values in SI units
* @data: pointer to the start of the scan
* @channels: information about the channels.
* Note: size_from_channelarray must have been called first
* to fill the location offsets.
* @num_channels: number of channels
**/
void process_scan(char *data,
struct iio_channel_info *channels,
int num_channels)
{
int k;

for (k = 0; k < num_channels; k++)
switch (channels[k].bytes) {
/* only a few cases implemented so far */
case 1:
print1byte(*(uint8_t *)(data + channels[k].location),
&channels[k]);
break;
case 2:
print2byte(*(uint16_t *)(data + channels[k].location),
&channels[k]);
break;
case 4:
print4byte(*(uint32_t *)(data + channels[k].location),
&channels[k]);
break;
case 8:
print8byte(*(uint64_t *)(data + channels[k].location),
&channels[k]);
break;
default:
break;
}
printf("\n");
}

void print_usage(void)
{
fprintf(stderr, "Usage: generic_buffer [options]...\n"
"Capture, convert and output data from IIO device buffer\n"
" -c <n> Do n conversions\n"
" -e Disable wait for event (new data)\n"
" -g Use trigger-less mode\n"
" -l <n> Set buffer length to n samples\n"
" -n <name> Set device name (mandatory)\n"
" -t <name> Set trigger name\n"
" -w <n> Set delay between reads in us (event-less mode)\n");
}

int main(int argc, char **argv)
{
unsigned long num_loops = 2;
unsigned long timedelay = 1000000;
unsigned long buf_len = 128;

int ret, c, i, j, toread;
int fp;

int num_channels;
char *trigger_name = NULL, *device_name = NULL;
char *dev_dir_name, *buf_dir_name;

int datardytrigger = 1;
char *data;
ssize_t read_size;
int dev_num, trig_num;
char *buffer_access;
int scan_size;
int noevents = 0;
int notrigger = 0;
char *dummy;

struct iio_channel_info *channels;

while ((c = getopt(argc, argv, "c:egl:n:t:w:")) != -1) {
switch (c) {
case 'c':
errno = 0;
num_loops = strtoul(optarg, &dummy, 10);
if (errno)
return -errno;

break;
case 'e':
noevents = 1;
break;
case 'g':
notrigger = 1;
break;
case 'l':
errno = 0;
buf_len = strtoul(optarg, &dummy, 10);
if (errno)
return -errno;

break;
case 'n':
device_name = optarg;
break;
case 't':
trigger_name = optarg;
datardytrigger = 0;
break;
case 'w':
errno = 0;
timedelay = strtoul(optarg, &dummy, 10);
if (errno)
return -errno;
break;
case '?':
print_usage();
return -1;
}
}

if (!device_name) {
fprintf(stderr, "Device name not set\n");
print_usage();
return -1;
}

/* Find the device requested */
dev_num = find_type_by_name(device_name, "iio:device");
if (dev_num < 0) {
fprintf(stderr, "Failed to find the %s\n", device_name);
return dev_num;
}

printf("iio device number being used is %d\n", dev_num);

ret = asprintf(&dev_dir_name, "%siio:device%d", iio_dir, dev_num);
if (ret < 0)
return -ENOMEM;

if (!notrigger) {
if (!trigger_name) {
/*
* Build the trigger name. If it is device associated
* its name is <device_name>_dev[n] where n matches
* the device number found above.
*/
ret = asprintf(&trigger_name,
"%s-dev%d", device_name, dev_num);
if (ret < 0) {
ret = -ENOMEM;
goto error_free_dev_dir_name;
}
}

/* Verify the trigger exists */
trig_num = find_type_by_name(trigger_name, "trigger");
if (trig_num < 0) {
fprintf(stderr, "Failed to find the trigger %s\n",
trigger_name);
ret = trig_num;
goto error_free_triggername;
}

printf("iio trigger number being used is %d\n", trig_num);
} else {
printf("trigger-less mode selected\n");
}

/*
* Parse the files in scan_elements to identify what channels are
* present
*/
ret = build_channel_array(dev_dir_name, &channels, &num_channels);
if (ret) {
fprintf(stderr, "Problem reading scan element information\n"
"diag %s\n", dev_dir_name);
goto error_free_triggername;
}
if (!num_channels) {
fprintf(stderr,
"No channels are enabled, we have nothing to scan.\n");
fprintf(stderr, "Enable channels manually in "
FORMAT_SCAN_ELEMENTS_DIR
"/*_en and try again.\n", dev_dir_name);
ret = -ENOENT;
goto error_free_triggername;
}

/*
* Construct the directory name for the associated buffer.
* As we know that the lis3l02dq has only one buffer this may
* be built rather than found.
*/
ret = asprintf(&buf_dir_name,
"%siio:device%d/buffer", iio_dir, dev_num);
if (ret < 0) {
ret = -ENOMEM;
goto error_free_channels;
}

if (!notrigger) {
printf("%s %s\n", dev_dir_name, trigger_name);
/*
* Set the device trigger to be the data ready trigger found
* above
*/
ret = write_sysfs_string_and_verify("trigger/current_trigger",
dev_dir_name,
trigger_name);
if (ret < 0) {
fprintf(stderr,
"Failed to write current_trigger file\n");
goto error_free_buf_dir_name;
}
}

/* Setup ring buffer parameters */
ret = write_sysfs_int("length", buf_dir_name, buf_len);
if (ret < 0)
goto error_free_buf_dir_name;

/* Enable the buffer */
ret = write_sysfs_int("enable", buf_dir_name, 1);
if (ret < 0) {
fprintf(stderr,
"Failed to enable buffer: %s\n", strerror(-ret));
goto error_free_buf_dir_name;
}

scan_size = size_from_channelarray(channels, num_channels);
data = malloc(scan_size * buf_len);
if (!data) {
ret = -ENOMEM;
goto error_free_buf_dir_name;
}

ret = asprintf(&buffer_access, "/dev/iio:device%d", dev_num);
if (ret < 0) {
ret = -ENOMEM;
goto error_free_data;
}

/* Attempt to open non blocking the access dev */
fp = open(buffer_access, O_RDONLY | O_NONBLOCK);
if (fp == -1) { /* TODO: If it isn't there make the node */
ret = -errno;
fprintf(stderr, "Failed to open %s\n", buffer_access);
goto error_free_buffer_access;
}

for (j = 0; j < num_loops; j++) {
if (!noevents) {
struct pollfd pfd = {
.fd = fp,
.events = POLLIN,
};

ret = poll(&pfd, 1, -1);
if (ret < 0) {
ret = -errno;
goto error_close_buffer_access;
} else if (ret == 0) {
continue;
}

toread = buf_len;
} else {
usleep(timedelay);
toread = 64;
}

read_size = read(fp, data, toread * scan_size);
if (read_size < 0) {
if (errno == EAGAIN) {
fprintf(stderr, "nothing available\n");
continue;
} else {
break;
}
}
for (i = 0; i < read_size / scan_size; i++)
process_scan(data + scan_size * i, channels,
num_channels);
}

/* Stop the buffer */
ret = write_sysfs_int("enable", buf_dir_name, 0);
if (ret < 0)
goto error_close_buffer_access;

if (!notrigger)
/* Disconnect the trigger - just write a dummy name. */
ret = write_sysfs_string("trigger/current_trigger",
dev_dir_name, "NULL");
if (ret < 0)
fprintf(stderr, "Failed to write to %s\n",
dev_dir_name);

error_close_buffer_access:
if (close(fp) == -1)
perror("Failed to close buffer");

error_free_buffer_access:
free(buffer_access);
error_free_data:
free(data);
error_free_buf_dir_name:
free(buf_dir_name);
error_free_channels:
for (i = num_channels - 1; i >= 0; i--) {
free(channels[i].name);
free(channels[i].generic_name);
}
free(channels);
error_free_triggername:
if (datardytrigger)
free(trigger_name);

error_free_dev_dir_name:
free(dev_dir_name);

return ret;
}



Regards,
John

> To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/4a2ef8fc-e9a5-7239-b454-61fd164ef667%40gmail.com.

[justin...@gmail.com]

[John Syne]

See the answer to your posting from yesterday.

Regards,

John

--
For more options, visit http://beagleboard.org/discuss
---
You received this message because you are subscribed to the Google Groups "BeagleBoard" group.
To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/b9a4e067-de33-46d1-a3bc-cc9a5d556643%40googlegroups.com.

[Justin Reina]

Hi John,
 I hope you know how dang excited I was to brush into your code response earlier this week, whilst at work as I browsed my Gmail inbox - sheesh & wow!!!! I got home though and could not find these search paths!

Issue: I cannot find /iio or /device0 on my BBB

Useful Context:

root@beaglebone:/# pwd
/
root@beaglebone:/# find / -type d -name iio
/lib/modules/4.4.9-ti-r25/kernel/drivers/iio
/lib/modules/4.4.9-ti-r25/kernel/drivers/staging/iio
/usr/src/linux-headers-4.4.9-ti-r25/tools/iio
/usr/src/linux-headers-4.4.9-ti-r25/drivers/iio
/usr/src/linux-headers-4.4.9-ti-r25/drivers/staging/iio
/usr/src/linux-headers-4.4.9-ti-r25/include/config/iio
/usr/src/linux-headers-4.4.9-ti-r25/include/config/hid/sensor/iio
/usr/src/linux-headers-4.4.9-ti-r25/include/config/sensors/iio
/usr/src/linux-headers-4.4.9-ti-r25/include/linux/iio
/usr/src/linux-headers-4.4.9-ti-r25/include/dt-bindings/iio
/usr/src/linux-headers-4.4.9-ti-r25/include/uapi/linux/iio
/opt/source/dtb-4.4-ti/Bindings/iio
/opt/source/dtb-4.4-ti/Bindings/staging/iio
/opt/source/dtb-4.4-ti/include/dt-bindings/iio
root@beaglebone:/# find / -type d -name device0
root@beaglebone:/# find / -type d -name device0
root@beaglebone:/# find / -type d -name scan_elements

Question: What is the cause here of these paths not showing up? I am running Jessie 8.4, grabbed and flashed earlier this week!

Thanks again for your help here John :)

-Justin
  justin...@gmail.com

[Justin Reina]

Here is a case where iio was not installed by default -

• https://gist.github.com/matthewmcneely/bf44655c74096ff96475

thoughts?

-J

[Robert Nelson]

in /boot/uEnv.txt, add:

cape_enable=bone_capemgr.enable_partno=BB-ADC

and reboot..

Regards,

--

Robert Nelson
https://rcn-ee.com/

[Justin Reina]

Robert, thank you!!!! Here is my new report running the same find tests -

steps today

1. opened up /boot/uEnv.txt copy on local PC, inspected contents
2. Pulled a copy of uEnv.txt to PC, updated with recommendation, reloaded, rebooted
3. Did same terminal test

    root@beaglebone:~# cd ..

    root@beaglebone:/# pwd
    /
    root@beaglebone:/# find / -type d -name iio
    /lib/modules/4.4.9-ti-r25/kernel/drivers/iio
    /lib/modules/4.4.9-ti-r25/kernel/drivers/staging/iio
    /usr/src/linux-headers-4.4.9-ti-r25/tools/iio
    /usr/src/linux-headers-4.4.9-ti-r25/drivers/iio
    /usr/src/linux-headers-4.4.9-ti-r25/drivers/staging/iio
    /usr/src/linux-headers-4.4.9-ti-r25/include/config/iio
    /usr/src/linux-headers-4.4.9-ti-r25/include/config/hid/sensor/iio
    /usr/src/linux-headers-4.4.9-ti-r25/include/config/sensors/iio
    /usr/src/linux-headers-4.4.9-ti-r25/include/linux/iio
    /usr/src/linux-headers-4.4.9-ti-r25/include/dt-bindings/iio
    /usr/src/linux-headers-4.4.9-ti-r25/include/uapi/linux/iio

    /sys/bus/iio
    /sys/kernel/debug/iio

    root@beaglebone:/# find / -type d -name device0
    root@beaglebone:/# find / -type d -name scan_elements

    /sys/devices/platform/ocp/44e0d000.tscadc/TI-am335x-adc/iio:device0/scan_elements

This ROCKS!

I will post up my final results this weekend - but thank you for this fix Rob!!!!

-J :)!