I am looking at using the i2c functionality of the Onion 2+ to be able to "detect" connect i2c slaves. unfortunately my tests with both python i2c library and c library both show that the omega returns "success" when reading and writing to an i2c slave that is not even there.

Does anyone know how to use i2c to detect if a slave is valid or not? i.e. If I try to "address" i2c slave "0x21" which is definitely not connected, how can I get some sort of error?

Thanks,

Just some feedback if you happen to stumble across this topic in desperation. So my analysis is that there must be a bug with the Onion 2 I2C implementation. With that said @t-gabor had a thread that described how he managed to overcome some of the i2c limitations by moving to a "bit-banged" i2c approach.

For those interested the following method was used on a Omega Onion 2+ (firmware v0.1.10-b160):

1. Install the relevant kernal modules (Thanks @t-gabor for compiling):

• kmod-i2c-gpio-custom_4.4.46-2_mipsel_24kc.ipk
• kmod-i2c-gpio_4.4.46-1_mipsel_24kc.ipk
• kmod-i2c-algo-bit_4.4.46-1_mipsel_24kc.ipk

This is done by downloading the above packages locally and running them in:
opkg install --force-depends kmod-i2c-algo-bit_4.4.46-1_mipsel_24kc.ipk
opkg install --force-depends kmod-i2c-gpio_4.4.46-1_mipsel_24kc.ipk
opkg install --force-depends kmod-i2c-gpio-custom_4.4.46-2_mipsel_24kc.ipk

the --force-depends is required as the onion thinks the kernel is at a too low version. if you are interested you can run:

root@Omega-XXXX:~# opkg list-installed | grep kernel
kernel - 4.4.46-1-611bddde2031bc44b7d050f62495d772

In order to get the current kernel version, which you will find the last section of numbers are lower that the expected value for the compiled packages above.

Anyhow what confused me for a good few hours was that the opkg install will show errors at the end even though it was successful (i.e. notice the "Installing" and "Configuring" sections):

root@Omega-XXXX:~/ipk# opkg install --force-depends kmod-i2c-algo-bit_4.4.46-1_mipsel_24kc.ipk
Installing kmod-i2c-algo-bit (4.4.46-1) to root...
Configuring kmod-i2c-algo-bit.
Collected errors:
 * satisfy_dependencies_for: Cannot satisfy the following dependencies for kmod-i2c-algo-bit:
 *      kernel (= 4.4.46-1-d0a487fc7d1c9f083b7de0fb8c2a7c07) *

Once these modules are installed we need to load them using the following commands:

omega2-ctrl gpiomux set i2c gpio
insmod i2c-algo-bit
insmod i2c-gpio
insmod i2c-gpio-custom bus0=1,5,4

with that you can now try the newly created /dev/i2c-1 device:

i2cdetect -y 1

And vola:

root@Omega-XXXX:~# i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Anyhow to wrap things up you can do this setup automatically at bootup with the following init.d script. create using vi in /etc/init.d/I2Cbb

#!/bin/sh /etc/rc.common
# Creates bit-banged i2c-device /dev/i2c-1 on pins 5,4.
# NOTE: This hides /dev/i2c-0!

START=98
STOP=97

start() {
        omega2-ctrl gpiomux set i2c gpio
        insmod i2c-algo-bit
        insmod i2c-gpio
        insmod i2c-gpio-custom bus0=1,5,4
}

stop() {
        rmmod i2c-gpio-custom
        rmmod i2c-gpio
        rmmod i2c-algo-bit
        omega2-ctrl gpiomux set i2c i2c
}

restart()
{
    stop
    start
}

And another hour or so of frustration and rebooting reminded me again of missing the basics, do not forget to enable and make executable the script!

chmod 755 /etc/init.d/I2Cbb
/etc/init.d/I2Cbb enable

*** EDIT ***
On an final note, using bitbanged I2C allows you to set the Onion I2C bus clock speed (SCL). To do this add the extra parameter to the the init.d script

insmod i2c-gpio-custom bus0=1,5,4,x

where x is is number based on the following formula:

I2C speed (kHz) = 500 / x 

Cheers,
UFD

I'm still unable to fix my related problem with write a byte wait 8ms then read 5 bytes without specifying register.
http://community.onion.io/topic/2674/access-to-i2c-low-level-calls-through-python-onioni2c

there seems also to still be a open drain issue
https://community.onion.io/topic/2603/omega2-i2c-bus-is-not-open-drain

Why hasn't this been fixed in Omega2+? I have scanned several posts in the forum that probably has problems that are related to this. I2C is a vital bus doing smart IoT stuff for real. So if Onion would like to be part of commercial projects I2C needs to have top priority.
Could any of the staff comment?

If for example you wanted two I2C busses, you would do that like this.

Example: using GPIO 14 for the second SDA and GPIO 16 for the 2nd SCL

insmod i2c-gpio-custom bus0=1,5,4 bus1=2,14,16

and you can then verify them with

i2cdetect -y 1

and

i2cdetect -y 2

Im glad you guys found this useful!

@Jeff-Seese Thanks for the additional information on spinning up multiple I2C channels (useful when you have fixed I2C address based devices).

@Jan-Breuer I will certainly look into this. It would be amazing if "real" I2C worked on the Omega.

Kind Regards,
UFD

How I can use these kmod's with another version of kernel?
Now I have latest firmware and the kernel version is 4.4.74.

kmod-i2c-gpio-custom_4.4.46-2_mipsel_24kc.ipk
kmod-i2c-gpio_4.4.46-1_mipsel_24kc.ipk
kmod-i2c-algo-bit_4.4.46-1_mipsel_24kc.ipk

There is no longer a b160 image at: http://repo.onion.io/omega2/images/ for some mysterious reason.

I have tried b159, but it gives me an "unable to open mmap file" error when I run "omega2-ctrl gpiomux set i2c gpio".

b175 gives me a "failed to find i2c-algo-bit" error when I run "insmod i2c-algo-bit"

@Sergiy-Tarasov, I have had some success using what is most likely a hack and not recommended.

1. Uncomment line 1 "reboot_core" in the file /etc/opkg/distfeeds.conf
2. opkg update
3. opkg --force-depends install kmod-i2c-gpio-custom
   Now the hack, because it was for a higher kenel version the libraries are installed to /lib/module/<kenel-version> so we need to copy them across to the current version, in my case:
4. cp /lib/modules/4.4.131/* /lib/4.47/

Then proceed with the insmod as before.

Regards,
UFD

• The i2cdetect command is now supported
• clock stretching is supported
• support for unlimited message length
• support for repeated start sequences

Check out this blog post for more details

@Ammar-Assad wrote

it is still unclear for me how to controll clock speed, it is alway 100 kHz

Clock stretching is not clear; i.e how to change clock for i2c, in my case it is 100 kHz and I wan to chage it

As you know the original I2C communication speed (I2C Standard mode) was defined with a maximum of 100 kbit per second and the SCL clock is always determined / generated by the I2C master.
The clock stretching is a completely different thing.

• Omega2(+) default 100kHz
  40MHz / 400 = 100kHz
  400 = 0x190
  0x8190800F

devmem 0x10000940
0x8190800F

• set to 400kHz
  40MHz / 100 = 400kHz
  100 = 0x64
  0x8064800F

devmem 0x10000940 32 0x8064800F

devmem 0x10000940
0x8064800F

Good luck!

0x10000940

Ooops! devmem not found unfortunately !

# Omega2+
root@Omega-99A5:/# oupgrade -v
> Device Firmware Version: 0.2.2 b200

root@Omega-99A5:/# cd ~
root@Omega-99A5:~# wget https://www.busybox.net/downloads/binaries/1.28.1-defconfig-multiarch/busybox-mipsel
root@Omega-99A5:~# chmod +x busybox-mipsel

root@Omega-99A5:~# ./busybox-mipsel
BusyBox v1.28.1 (2018-02-15 14:34:02 CET) multi-call binary.
BusyBox is copyrighted by many authors between 1998-2015.
Licensed under GPLv2. See source distribution for detailed
copyright notices.

Usage: busybox [function [arguments]...]
   or: busybox --list[-full]
   or: busybox --install [-s] [DIR]
   or: function [arguments]...

	BusyBox is a multi-call binary that combines many common Unix
	utilities into a single executable.  Most people will create a
	link to busybox for each function they wish to use and BusyBox
	will act like whatever it was invoked as.

Currently defined functions:
	[, [[, acpid, add-shell, addgroup, adduser, adjtimex, arch, arp, arping, ash, awk, base64, basename, beep, blkdiscard, blkid,
	blockdev, bootchartd, brctl, bunzip2, bzcat, bzip2, cal, cat, chat, chattr, chgrp, chmod, chown, chpasswd, chpst, chroot,
	chrt, chvt, cksum, clear, cmp, comm, conspy, cp, cpio, crond, crontab, cryptpw, cttyhack, cut, date, dc, dd, deallocvt,
	delgroup, deluser, depmod, devmem, df, dhcprelay, diff, dirname, dmesg, dnsd, dnsdomainname, dos2unix, dpkg, dpkg-deb, du,
	dumpkmap, dumpleases, echo, ed, egrep, eject, env, envdir, envuidgid, ether-wake, expand, expr, factor, fakeidentd, fallocate,
	false, fatattr, fbset, fbsplash, fdflush, fdformat, fdisk, fgconsole, fgrep, find, findfs, flock, fold, free, freeramdisk,
	fsck, fsck.minix, fsfreeze, fstrim, fsync, ftpd, ftpget, ftpput, fuser, getopt, getty, grep, groups, gunzip, gzip, halt, hd,
	hdparm, head, hexdump, hexedit, hostid, hostname, httpd, hush, hwclock, i2cdetect, i2cdump, i2cget, i2cset, id, ifconfig,
	ifdown, ifenslave, ifplugd, ifup, inetd, init, insmod, install, ionice, iostat, ip, ipaddr, ipcalc, ipcrm, ipcs, iplink,
	ipneigh, iproute, iprule, iptunnel, kbd_mode, kill, killall, killall5, klogd, last, less, link, linux32, linux64, linuxrc, ln,
	loadfont, loadkmap, logger, login, logname, logread, losetup, lpd, lpq, lpr, ls, lsattr, lsmod, lsof, lspci, lsscsi, lsusb,
	lzcat, lzma, lzop, makedevs, makemime, man, md5sum, mdev, mesg, microcom, mkdir, mkdosfs, mke2fs, mkfifo, mkfs.ext2,
	mkfs.minix, mkfs.vfat, mknod, mkpasswd, mkswap, mktemp, modinfo, modprobe, more, mount, mountpoint, mpstat, mt, mv, nameif,
	nanddump, nandwrite, nbd-client, nc, netstat, nice, nl, nmeter, nohup, nproc, nsenter, nslookup, ntpd, nuke, od, openvt,
	partprobe, passwd, paste, patch, pgrep, pidof, ping, ping6, pipe_progress, pivot_root, pkill, pmap, popmaildir, poweroff,
	powertop, printenv, printf, ps, pscan, pstree, pwd, pwdx, raidautorun, rdate, rdev, readahead, readlink, readprofile,
	realpath, reboot, reformime, remove-shell, renice, reset, resize, resume, rev, rm, rmdir, rmmod, route, rpm, rpm2cpio,
	rtcwake, run-init, run-parts, runlevel, runsv, runsvdir, rx, script, scriptreplay, sed, sendmail, seq, setarch, setconsole,
	setfattr, setfont, setkeycodes, setlogcons, setpriv, setserial, setsid, setuidgid, sh, sha1sum, sha256sum, sha3sum, sha512sum,
	showkey, shred, shuf, slattach, sleep, smemcap, softlimit, sort, split, ssl_client, start-stop-daemon, stat, strings, stty,
	su, sulogin, sum, sv, svc, svlogd, swapoff, swapon, switch_root, sync, sysctl, syslogd, tac, tail, tar, taskset, tcpsvd, tee,
	telnet, telnetd, test, tftp, tftpd, time, timeout, top, touch, tr, traceroute, traceroute6, true, truncate, tty, ttysize,
	tunctl, ubiattach, ubidetach, ubimkvol, ubirename, ubirmvol, ubirsvol, ubiupdatevol, udhcpc, udhcpd, udpsvd, uevent, umount,
	uname, unexpand, uniq, unix2dos, unlink, unlzma, unshare, unxz, unzip, uptime, users, usleep, uudecode, uuencode, vconfig, vi,
	vlock, volname, w, wall, watch, watchdog, wc, wget, which, who, whoami, whois, xargs, xxd, xz, xzcat, yes, zcat, zcip

root@Omega-99A5:~# ./busybox-mipsel devmem 0x10000940
0x818F800F

root@Omega-99A5:~# ./busybox-mipsel devmem 0x10000940 32 0x8064800F
root@Omega-99A5:~# ./busybox-mipsel devmem 0x10000940
0x8064800F

FW 0.2.2 b200 - presently the divider is '0x18F = 399' instead of '0x190 = 400'.
Please ask one of Onion administrators ( @Zheng-Han @Lazar-Demin @Pavel-Metrokhin) why

./busybox-mipsel devmem 0x10000940 32 0x8064800F

I am very grateful to you, it worked fine ...