I2C from 8 pin connector

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I2C from 8 pin connector

Unread post by taylorjtt » Tue Feb 04, 2014 3:06 am

I have looked at the schematics and I can't figure out which I2C module (0,1 or 2) is connected to the 8-pin header. It looks like 0 is connected to the USB/PWR block, 1 is connected to the Audio Codec and 2 is connected to HDMI. Which one is connected to the 8-pin header and which pins are SDA and SCL?

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Re: I2C from 8 pin connector

Unread post by odroid » Tue Feb 04, 2014 3:11 pm

Software I2C bit-bang with GPIO.

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Re: I2C from 8 pin connector

Unread post by bennyber » Sun Feb 09, 2014 5:44 pm

odroid wrote:Software I2C bit-bang with GPIO.
Can you be more specific?
Please, tell me exactly what pins are used for I2C communication.

It will be nice if you also can add some code that demonstrates how
to enable and use I2C protocol.

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Re: I2C from 8 pin connector

Unread post by odroid » Sun Feb 09, 2014 7:50 pm

Did you check the schematics and example in this link?
http://www.hardkernel.com/main/products ... &tab_idx=2

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Re: I2C from 8 pin connector

Unread post by bennyber » Tue Feb 11, 2014 1:37 am

Hello

I checked the schematics but I'm not an engineer and I don't
understand it. Is there a simpler manual that explains where each pin goes
and how to enable/use I2C?

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Re: I2C from 8 pin connector

Unread post by homedroid » Tue Feb 11, 2014 10:30 am

odroid wrote:Did you check the schematics and example in this link?
http://www.hardkernel.com/main/products ... &tab_idx=2
Hello,

I'm trying to figure out how I could control the gpio on the U3 IO shield, but I can't quite make the /sys/class/gpiochipXX to actual pins...

The code given below the schematic on the page - well I don't have anything for the 289-304 range in /sys/class/

What am I missing?

*EDIT*

sudo echo tca6416 0x20 > /sys/devices/platform/i2c-gpio.4/i2c-4/new_device doesn't work.. it seems that one has to do a sudo -s and then the echo..

Now I've got a gpio290 where I can change direction and set value.. cool. and it actually works!

gpio290 is P01 on the board

echo out > /sys/class/gpio/gpio290/direction
echo 0 > /sys/class/gpio/gpio290/value
echo 1 > /sys/class/gpio/gpio290/value

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Re: I2C from 8 pin connector

Unread post by odroid » Tue Feb 11, 2014 11:44 am

Please also refer the ODROID Magazine - February Issue.
http://forum.odroid.com/viewtopic.php?f=74&t=3027

There is a C/C++ example code to use the IO shield pins.

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Re: I2C from 8 pin connector

Unread post by homedroid » Wed Feb 12, 2014 8:15 am

Yes, I want through it quickly, I'll spend more time on this shortly.

And I do have some (easy) questions .. :D

What is the reset button supposed to do on the U3 IO shield?

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Re: I2C from 8 pin connector

Unread post by mdrjr » Wed Feb 12, 2014 9:14 am

homedroid wrote:Yes, I want through it quickly, I'll spend more time on this shortly.

And I do have some (easy) questions .. :D

What is the reset button supposed to do on the U3 IO shield?
The same as it does on a Arduino :P

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Re: I2C from 8 pin connector

Unread post by odroid » Wed Feb 12, 2014 10:07 am

To upload your Sketch file to Atmega328 MCU, the MCU should enter into boot loader mode to receive the compiled sketch file.
It is a DTR emulation in the UART interface.

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Re: I2C from 8 pin connector

Unread post by JuanJ » Wed Feb 12, 2014 2:11 pm

Hello,

I have 1.8V compliant ICs that I wanted to connect directly to the I2C port on the 8 pin connector. But from what I see in previous answers, none of the 8 I2C modules available in the Exinos 4412 is redirected to the 8pin port, and I have to do software simulation to GPIO. I just wanted to confirm that, because the technical review of ODROID U3 explicitly states that an I2C port is available in the 8pin connector... (http://dn.odroid.com/homebackup/201312201108358947.jpg)

Also I'm having a hard time trying to correlate the pin-names from the U3 schematic with the port names in the Exynos 4412 users guide (locking for information on the I2C of course). Actually I couldn't find any pin out description or something like it in the Users Guide. So I think I'm missing out something here... if you could explain that to me i would be great, or there are other tech refs I can consult?.

Because from what I see here, i'm obligated to use the arduino expansion board or build my own usb/uart expansion system. And I don't want to do neither, because it would cost me time, money and add complexity to the overall system. I just want to connect my ICs to the odroid directly.

Thanks!

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Re: I2C from 8 pin connector

Unread post by odroid » Wed Feb 12, 2014 4:07 pm

If you see the schematics of the IO shield, you can find which pins on the 8-Pin connector are used for I2C.
http://www.hardkernel.com/main/products ... &tab_idx=2
2 GPIOs are connected to the I2C IO Expander IC as SCL/SDA.

If you refer the source code of gpio-pca953x device driver, you can learn how to use the software driven I2C.

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Re: I2C from 8 pin connector

Unread post by Digimaster » Thu Feb 13, 2014 2:59 am

Very Interesting.

If I understood right, there should be some /sys/class/gpio*** virtual devices which are mapped directly to SCL, SDA io pins on 8-pin connector.
Then, if I going to use only 2 IO signals I don't need expansion board. Just connect directly to U3 pins, right?
If it so, which ones?

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Re: I2C from 8 pin connector

Unread post by mdrjr » Thu Feb 13, 2014 3:04 am

On the shield datasheet..


GPX1.0 is SDA and GPX1.1 is SDL.

On the IO Shield those are on the JP3 header.

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Re: I2C from 8 pin connector

Unread post by Digimaster » Thu Feb 13, 2014 4:15 am

Anyone succeeded finding /sys/class/gpio??? correspondence to SCL, SDA?

EDIT

cat /sys/class/gpio/gpiochip199/label

gives
GPX1

but I cannot allocate resource: write error: Device or resource busy.
dmesg shows that i2c-gpio.4 allocated 199 and 200.
i2c-gpio is a kernel module, so I need somehow blacklisted it.
Looking further... I don't think it is possible without kernel rebuild.

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Re: I2C from 8 pin connector

Unread post by JuanJ » Fri Feb 14, 2014 2:11 pm

Suppose the gpio-i2c is working ok (thats not true for me yet :s)... How is the performance impact of using software driven I2C. If I want to read a 3 axis gyroscope+acelerometer for example at 1000hz data rate, I would be using almost all the bandwidth of the bus (supposing 400KHz clock rate), that means the processor will hang doing gpio bit bang? Or the kernel will do just fine?
If the first it's true, i guess I'll just have to use another interface, like uart. What do you recommend, for achieving the better performance?
Thanks in advance!

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Re: I2C from 8 pin connector

Unread post by odroid » Fri Feb 14, 2014 2:36 pm

We coudl use an accelerometer with a software driven I2C in other projects and there was no problem.
I think the software bitbang driver in the modern kernel is very well implemented to minimize the system overhead.

But, if your sensor can supports the UART interface too, it will be more safe.

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Re: I2C from 8 pin connector

Unread post by Digimaster » Sun Feb 23, 2014 12:47 am

There is a possibility to use 2 gpio signals on U3 without extra hardware.
Only two pins can be accessed!
gpio_u3.jpg
U3 gpio without extra hardware
First of all it is required to disable i2c bit-bang driver plus kernel rebuild.

After that use common method:

Code: Select all

echo 199 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio199/direction
echo 1 > /sys/class/gpio/gpio199/value
echo 0 > /sys/class/gpio/gpio199/value
echo 199 > /sys/class/gpio/unexport

...Same for gpio200

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Re: I2C from 8 pin connector

Unread post by odroid » Sun Feb 23, 2014 3:17 pm

Thank you for the sharing. :o

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Re: I2C from 8 pin connector

Unread post by mbonamusa » Wed Mar 12, 2014 3:32 am

If I use Digimaster instruccions, when I execute (as root):
echo 199 > /sys/class/gpio/export
I get next message:
echo: write error: Device or resource busy

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Re: I2C from 8 pin connector

Unread post by mdrjr » Wed Mar 12, 2014 4:23 am

mbonamusa wrote:If I use Digimaster instruccions, when I execute (as root):
echo 199 > /sys/class/gpio/export
I get next message:
echo: write error: Device or resource busy
Have you disabled the i2c bitbang on the kernel sources? As he mentioned?

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Re: I2C from 8 pin connector

Unread post by Digimaster » Wed Mar 12, 2014 3:29 pm

In addition to my previous post.
This is a powerful external device control. I made a simple gpio amplifier for two devices on/off.
Just choose appropriate optical relay in order to the required electric current.
Circuits:
Amplifier.png
Circuits
Amplifier.png (33.95 KiB) Viewed 16586 times
Debugging :)
20140228_175258.jpg
Final amplifier without relay attached.
20140228_183404.jpg
Last edited by Digimaster on Sun Mar 30, 2014 2:34 pm, edited 1 time in total.

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Re: I2C from 8 pin connector

Unread post by mbonamusa » Wed Mar 12, 2014 6:00 pm

mdrjr wrote:
mbonamusa wrote:If I use Digimaster instruccions, when I execute (as root):
echo 199 > /sys/class/gpio/export
I get next message:
echo: write error: Device or resource busy
Have you disabled the i2c bitbang on the kernel sources? As he mentioned?
Sorry, I didn't pay attention on this.
Must I recompile kernel disabling i2c bitbang? In this way I'm not much linux expert to deal with kernel recompilation.

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Re: I2C from 8 pin connector

Unread post by Digimaster » Wed Mar 12, 2014 8:42 pm

Yes, you should disable i2c bitbang driver first to release gpio199, gpio200 direct access.

Actually, it's not so complicate. See http://forum.odroid.com/viewtopic.php?f=52&t=81
tutorial how to recompile kernel. Just replace to odroid-3.8.y for actual version.

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Re: I2C from 8 pin connector

Unread post by mbonamusa » Thu Mar 13, 2014 7:34 pm

If I use odroid-3.8.13, automatically I get the latest mdrjr update (3.8.13.18)?

Is there any possibility to recompile the kernel and then we can switch between i2c and gpio mode with the same kernel?

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Re: I2C from 8 pin connector

Unread post by Digimaster » Thu Mar 13, 2014 10:01 pm

If I understand right, the compiled kernel is zImage file + modules.
Bitbang driver is kernelmode, so you can precompile two versions (with and without) bitbang.
After that just copy required version zImage to /boot.

Someone please correct me if I wrong.

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Re: I2C from 8 pin connector

Unread post by msidd » Thu Mar 27, 2014 9:29 pm

As an addition to Digimasters post:

GPIO pins:
1: gpio199 -- GPX1.0 -- SDA
3: gpio200 -- GPX1.1 -- SCL
5: grio204 -- GPX1.5 -- no I²C binding
7: ground

This should work out-of-the-box:

Code: Select all

echo 204 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio204/direction
echo 1 > /sys/class/gpio/gpio204/value
echo 0 > /sys/class/gpio/gpio204/value
echo 204 > /sys/class/gpio/unexport

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Re: I2C from 8 pin connector

Unread post by memeka » Wed Apr 02, 2014 9:11 pm

Is it possible to use pins 4 & 6 (currently used for UART rx/tx) as GPIO?
Or similar?

Is it possible to mmap them and toggle them from a C program?
What are their addresses?
How about the addresses of other pins?
Thanks!

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Re: I2C from 8 pin connector

Unread post by mdrjr » Wed Apr 02, 2014 11:18 pm

memeka wrote:Is it possible to use pins 4 & 6 (currently used for UART rx/tx) as GPIO?
Or similar?

Is it possible to mmap them and toggle them from a C program?
What are their addresses?
How about the addresses of other pins?
Thanks!
It may be possible, you'll need to undo all the kernel + bootloader configs binding the uart port

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Re: I2C from 8 pin connector

Unread post by memeka » Thu Apr 03, 2014 5:58 am

Why boot loader?
Isn't that only for the UART connector?
Given that I mostly want gpio out, can't i do that with tx?

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Re: I2C from 8 pin connector

Unread post by mdrjr » Thu Apr 03, 2014 7:40 am

memeka wrote:Why boot loader?
Isn't that only for the UART connector?
Given that I mostly want gpio out, can't i do that with tx?
I think *needs to check* that there is partial initialization on the bootloader. If not, you have to disable that uart on the kernel.

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Re: I2C from 8 pin connector

Unread post by memeka » Thu Apr 03, 2014 9:31 am

So, I need to edit boot.scr to remove the UART console, then remove the tty uart console from inittab.
Then I have access to the serial port. But, this would be for the serial port on the UART connector, is it not?

I want to use the TX and RX on the expansion port, since I will NOT be using IO Shield and I need 4 GPIO pins for a stepper motor.
I got 3 pins already (gpx1.0, gpx1.1 and gpx1.5), so I need the last one.
Even a serial TX would be fine, since I just need to send a short logical "1" on the pin, with something like

Code: Select all

echo X > /dev/ttySAC1
So my question is, both the UART connector AND the UART tx rx from expansion port are ttySAC1 ?
And if possible, after freeing the UART from console, can I actually toggle e.g. TX pin 1 / 0 basically acting like digital output pin (e.g. keep TX continuously high)?
And also, what are the addresses of gpx1.0 and the tx/rx pins, because I want to use a C program with mmap and not the /sys filesystem.

Thanks!

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Re: I2C from 8 pin connector

Unread post by memeka » Thu Apr 03, 2014 9:59 am

Decided to use a shift register.
With 1 shift register + 3 GPIO you can extend to 8 GPIO, and more can be added if you cascade shift registers.

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Re: I2C from 8 pin connector

Unread post by Panzerknacker » Fri Apr 04, 2014 4:44 pm

What about using an I2C Port expander like PCF8574 (8 bits) on the two i2c pins?

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Re: I2C from 8 pin connector

Unread post by memeka » Fri Apr 04, 2014 8:18 pm

Panzerknacker wrote:What about using an I2C Port expander like PCF8574 (8 bits) on the two i2c pins?
sure, but i wanted something fast, and the shift registers were in stock in the electronics store, port expanders were not.

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Re: I2C from 8 pin connector

Unread post by bennyber » Mon Jun 02, 2014 3:56 am

Hello,

Can you, please, show what I must do and where
in order to disable i2c bitbang driver.
So it will be possible to release gpio199, gpio200 direct access.

Thanks.

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Re: I2C from 8 pin connector

Unread post by mdrjr » Mon Jun 02, 2014 4:01 am

bennyber wrote:Hello,

Can you, please, show what I must do and where
in order to disable i2c bitbang driver.
So it will be possible to release gpio199, gpio200 direct access.

Thanks.
Update your kernel.. its fixed..

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Re: I2C from 8 pin connector

Unread post by homedroid » Tue Jul 29, 2014 11:15 am

odroid wrote:Please also refer the ODROID Magazine - February Issue.
http://forum.odroid.com/viewtopic.php?f=74&t=3027

There is a C/C++ example code to use the IO shield pins.
Hi - just went through them (actually the ones dealing with the command lines on page 32-33 of the february issue of the magazine)...

and it does not seem to work for me... I am on Whisper 13.10;


modprobe gpio_pca953x

echo tca6416 0x20 > /sys/devices/platform/i2c-gpio.4/i2c-4/new_device
-bash: /sys/devices/platform/i2c-gpio.4/i2c-4/new_device: No such file or directory

Again, but now with .2 instead of .4

echo tca6416 0x20 > /sys/devices/platform/i2c-gpio.4/i2c-4/new_device
-bash: /sys/devices/platform/i2c-gpio.4/i2c-4/new_device: No such file or directory

dmesg
[ 822.826126] pca953x 2-0020: failed reading register
[ 822.826204] i2c i2c-2: new_device: Instantiated device tca6416 at 0x20

where any exports fail with

odroid@odroid:~$ echo 289 > /sys/class/gpio/export
-bash: echo: write error: No such device

any clues? thanx!

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Re: I2C from 8 pin connector

Unread post by odroid » Tue Jul 29, 2014 12:14 pm


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Re: I2C from 8 pin connector

Unread post by KC7NOA » Fri Jan 09, 2015 3:41 pm

Digimaster ...

What opticoupler did you use ?

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Re: I2C from 8 pin connector

Unread post by Digimaster » Thu Jan 15, 2015 5:12 pm

KC7NOA wrote:Digimaster ...

What opticoupler did you use ?
Sorry, I lost my papers... But you can use a wide range of them. The transistor I used is powerful enough to drive most of couplers.

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Re: I2C from 8 pin connector

Unread post by KC7NOA » Fri Jan 16, 2015 4:14 am

Digimaster wrote:
KC7NOA wrote:Digimaster ...

What opticoupler did you use ?
Sorry, I lost my papers... But you can use a wide range of them. The transistor I used is powerful enough to drive most of couplers.
ok .. thanks .. im going to try to use some level converters off of Ebay ( 231364797910 ) and see if they can drive an optocupler ....

I think these level converters can supply 50ma ....

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