[RFC] Driver for Arduino-as-I2C-adapter

[RFC] Driver for Arduino-as-I2C-adapter

[Bernhard Kraft]

Hi,

For a project I needed to communicate with external hardware via the I2C 
protocol. I took a look at the existing drivers in the linux kernel 
source "drivers/i2c/busses".

Instead of buying yet another interface dongle (this time for I2C) I 
decided to use an Arduino with an apropriate sketch as I2C adapter.

Currently I access the I2C adapter (Arduino) via a custom program 
reading/writing to /dev/ttyACM0.


Do you think it would make sense to add an I2C driver to the Linux 
kernel for an "Arduino as I2C adapter" solution?

Or could you propose another solution? Maybe just an "external" module 
like the nvidia kernel module?



greetings,
Bernhard
-- 
Wer nicht gelegentlich auch einmal kausalwidrige Dinge zu denken vermag,
wird seine Wissenschaft nie um eine neue Idee bereichern können.
Max Planck (1858-1947)
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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Alex Beregszaszi]

Hi Bernhard,

There are many cheap I2C adapter projects (mostly USB though). One of 
the simple ones (i2c-tiny-usb) is included in the kernel, while LinkM 
(https://github.com/todbot/LinkM) stayed userspace.

As regarding to cheap serial line based adapters, there are two I have 
seen before 
(http://www.gedanken.org.uk/electronics/rs232-converters/i2c.html and 
http://www.robot-electronics.co.uk/acatalog/USB_I2C.html) and both 
define a different protocol.

Personally I would suggest to try follow one of those protocols to avoid 
creating a new one and would be happy to see an open sourced Arduino 
sketch as well.

I am afraid handling serial devices within a i2c kernel driver might be 
tricky and purists probably dislike the idea.

Best,
Alex

Bernhard Kraft wrote:
> Hi,
>
> For a project I needed to communicate with external hardware via the 
> I2C protocol. I took a look at the existing drivers in the linux 
> kernel source "drivers/i2c/busses".
>
> Instead of buying yet another interface dongle (this time for I2C) I 
> decided to use an Arduino with an apropriate sketch as I2C adapter.
>
> Currently I access the I2C adapter (Arduino) via a custom program 
> reading/writing to /dev/ttyACM0.
>
>
> Do you think it would make sense to add an I2C driver to the Linux 
> kernel for an "Arduino as I2C adapter" solution?
>
> Or could you propose another solution? Maybe just an "external" module 
> like the nvidia kernel module?
>
>
>
> greetings,
> Bernhard
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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Bernhard Kraft]

Hi,

On 2015-05-18 15:00, Alex Beregszaszi wrote:

> There are many cheap I2C adapter projects (mostly USB though). One of
> the simple ones (i2c-tiny-usb) is included in the kernel  [...]

I knew of the OpenSource project i2c-tiny-usb. But sadly the hardware 
ist not sold anywhere (At least I didn't find vendors).


> As regarding to cheap serial line based adapters, there are two I have
> seen before [...]

None of them seems to have kernel drivers available. So I could stick to 
my own homebrewn Arduino solution.


> I am afraid handling serial devices within a i2c kernel driver might be
> tricky and purists probably dislike the idea.

Currently there is at least one driver for such a case already in the 
kernel: drivers/i2c/busses/i2c-taos-evm.c

I found it by "grep serio.h" in i2c/busses/. But this driver rather only 
supports SMBus which is kind of subset of I2C. Or you could call it I2C 
with more strict requirements upon timing and protocol.

In fact this would have been the driver I would have based my work on if 
someone said: Go on, this is a good thing to include in the kernel.


But for now I think I will just publish the Arduino sketch and a sample 
implementation on how to access I2C devices with it.



greetings,
Bernhard
-- 
Wer nicht gelegentlich auch einmal kausalwidrige Dinge zu denken vermag,
wird seine Wissenschaft nie um eine neue Idee bereichern können.
Max Planck (1858-1947)
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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Angelo Compagnucci]

Dear Bernhard Kraft,

2015-05-18 18:53 GMT+02:00 Bernhard Kraft <kraftb@think-open.at>:
> Hi,
>
> On 2015-05-18 15:00, Alex Beregszaszi wrote:
>
>> There are many cheap I2C adapter projects (mostly USB though). One of
>> the simple ones (i2c-tiny-usb) is included in the kernel  [...]
>
>
> I knew of the OpenSource project i2c-tiny-usb. But sadly the hardware ist
> not sold anywhere (At least I didn't find vendors).
>
>
>> As regarding to cheap serial line based adapters, there are two I have
>> seen before [...]
>
>
> None of them seems to have kernel drivers available. So I could stick to my
> own homebrewn Arduino solution.
>
>
>> I am afraid handling serial devices within a i2c kernel driver might be
>> tricky and purists probably dislike the idea.
>
>
> Currently there is at least one driver for such a case already in the
> kernel: drivers/i2c/busses/i2c-taos-evm.c
>
> I found it by "grep serio.h" in i2c/busses/. But this driver rather only
> supports SMBus which is kind of subset of I2C. Or you could call it I2C with
> more strict requirements upon timing and protocol.
>
> In fact this would have been the driver I would have based my work on if
> someone said: Go on, this is a good thing to include in the kernel.

Personally, I find the idea very interesting, Arduino is so common
that using it a usb/i2c bridge could benefit really a lot of people.
Actually I'm think also to spi!

> But for now I think I will just publish the Arduino sketch and a sample
> implementation on how to access I2C devices with it.

Probably we should stick to other protocol driver implementation, but
from a rapid analisys, this will be the second in kernel serial to i2c
adapter, so I think there is not such a string standard protocol in
this field.

Please publish your sketch, I think making the driver is really not a
complex matter!
Count on me for any help, I really like the idea to have my name on
such an interesting project!

Sincerely, Angelo

>
> greetings,
> Bernhard
> --
> Wer nicht gelegentlich auch einmal kausalwidrige Dinge zu denken vermag,
> wird seine Wissenschaft nie um eine neue Idee bereichern können.
> Max Planck (1858-1947)
> _______________________________________________
> devel mailing list
> devel@linuxdriverproject.org
> http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel



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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Alex Beregszaszi]

Hi,

Angelo Compagnucci wrote:
> Dear Bernhard Kraft,
>
> 2015-05-18 18:53 GMT+02:00 Bernhard Kraft<kraftb@think-open.at>:
>
>> But for now I think I will just publish the Arduino sketch and a sample
>> implementation on how to access I2C devices with it.
>
> Probably we should stick to other protocol driver implementation, but
> from a rapid analisys, this will be the second in kernel serial to i2c
> adapter, so I think there is not such a string standard protocol in
> this field.
>
> Please publish your sketch, I think making the driver is really not a
> complex matter!
> Count on me for any help, I really like the idea to have my name on
> such an interesting project!
I have  worked on some I2C drivers for Linux, as well as Arduino and 
searched for cheaper options countless times.  Yesterday's email made me 
to search again and really liked the way one of products I've mentioned 
was structured.

So I sat down and wrote an Arduino implementation of that specification 
just to see what the performance would be. You can find it at: 
https://github.com/axic/dtiic

Best,
Alex
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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Angelo Compagnucci]

Hi Alex,

2015-05-19 13:59 GMT+02:00 Alex Beregszaszi <alex@rtfs.hu>:
> Hi,
>
> Angelo Compagnucci wrote:
>
> Dear Bernhard Kraft,
>
> 2015-05-18 18:53 GMT+02:00 Bernhard Kraft <kraftb@think-open.at>:
>
> But for now I think I will just publish the Arduino sketch and a sample
> implementation on how to access I2C devices with it.
>
> Probably we should stick to other protocol driver implementation, but
> from a rapid analisys, this will be the second in kernel serial to i2c
> adapter, so I think there is not such a string standard protocol in
> this field.
>
> Please publish your sketch, I think making the driver is really not a
> complex matter!
> Count on me for any help, I really like the idea to have my name on
> such an interesting project!
>
> I have  worked on some I2C drivers for Linux, as well as Arduino and
> searched for cheaper options countless times.  Yesterday's email made me to
> search again and really liked the way one of products I've mentioned was
> structured.

Great! Looking at the kernel, the USB-ISS doesn't have a ready made
driver. This could be a counter argument cause we will use another I2C
over UART protocol.

> So I sat down and wrote an Arduino implementation of that specification just
> to see what the performance would be. You can find it at:
> https://github.com/axic/dtiic

I had a quick look at code and it seems simple, readable and fastest
at least to sustain the 400khz mode of i2c.

BTW, I'm thinking on making an arduino code compatible with some of
the already in kernel driver and i2c-tiny-usb could be a really valid
candidate. This way we could only ask for a .ino inclusion in mainline
with some sort of documentation on how to cook a homemade I2C over
UART bridge.

Sincerely, Angelo

>
> Best,
> Alex
>



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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Angelo Compagnucci]

Hi Alex,

2015-05-19 15:34 GMT+02:00 Angelo Compagnucci <angelo.compagnucci@gmail.com>:
> Hi Alex,
>
> 2015-05-19 13:59 GMT+02:00 Alex Beregszaszi <alex@rtfs.hu>:
>> Hi,
>>
>> Angelo Compagnucci wrote:
>>
>> Dear Bernhard Kraft,
>>
>> 2015-05-18 18:53 GMT+02:00 Bernhard Kraft <kraftb@think-open.at>:
>>
>> But for now I think I will just publish the Arduino sketch and a sample
>> implementation on how to access I2C devices with it.
>>
>> Probably we should stick to other protocol driver implementation, but
>> from a rapid analisys, this will be the second in kernel serial to i2c
>> adapter, so I think there is not such a string standard protocol in
>> this field.
>>
>> Please publish your sketch, I think making the driver is really not a
>> complex matter!
>> Count on me for any help, I really like the idea to have my name on
>> such an interesting project!
>>
>> I have  worked on some I2C drivers for Linux, as well as Arduino and
>> searched for cheaper options countless times.  Yesterday's email made me to
>> search again and really liked the way one of products I've mentioned was
>> structured.
>
> Great! Looking at the kernel, the USB-ISS doesn't have a ready made
> driver. This could be a counter argument cause we will use another I2C
> over UART protocol.
>
>> So I sat down and wrote an Arduino implementation of that specification just
>> to see what the performance would be. You can find it at:
>> https://github.com/axic/dtiic
>
> I had a quick look at code and it seems simple, readable and fastest
> at least to sustain the 400khz mode of i2c.
>
> BTW, I'm thinking on making an arduino code compatible with some of
> the already in kernel driver and i2c-tiny-usb could be a really valid
> candidate. This way we could only ask for a .ino inclusion in mainline
> with some sort of documentation on how to cook a homemade I2C over
> UART bridge.

The only downside of this approach is that we should write something
USB based, not UART, so it will limit the choice of usable Arduino
board to only the Leonardo.
I think we should stick for an serio based driver to be compatible
with all the boards.

I have no problem in writing such a driver, probably I will look into
this in the next few days.

Sincerely, Angelo

>
> Sincerely, Angelo
>
>>
>> Best,
>> Alex
>>
>
>
>
> --
> Profile: http://it.linkedin.com/in/compagnucciangelo



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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Alex Beregszaszi]

Hi Angelo,

Angelo Compagnucci wrote:
> Hi Alex,
>
> 2015-05-19 15:34 GMT+02:00 Angelo Compagnucci<angelo.compagnucci@gmail.com>:
>> Hi Alex,
>>
>> 2015-05-19 13:59 GMT+02:00 Alex Beregszaszi<alex@rtfs.hu>:
>>> Hi,
>>>
>>> Angelo Compagnucci wrote:
>>>
>>> Dear Bernhard Kraft,
>>>
>>> 2015-05-18 18:53 GMT+02:00 Bernhard Kraft<kraftb@think-open.at>:
>>>
>>> But for now I think I will just publish the Arduino sketch and a sample
>>> implementation on how to access I2C devices with it.
>>>
>>> Probably we should stick to other protocol driver implementation, but
>>> from a rapid analisys, this will be the second in kernel serial to i2c
>>> adapter, so I think there is not such a string standard protocol in
>>> this field.
>>>
>>> Please publish your sketch, I think making the driver is really not a
>>> complex matter!
>>> Count on me for any help, I really like the idea to have my name on
>>> such an interesting project!
>>>
>>> I have  worked on some I2C drivers for Linux, as well as Arduino and
>>> searched for cheaper options countless times.  Yesterday's email made me to
>>> search again and really liked the way one of products I've mentioned was
>>> structured.
>> Great! Looking at the kernel, the USB-ISS doesn't have a ready made
>> driver. This could be a counter argument cause we will use another I2C
>> over UART protocol.

I do plan to write a serio driver.  Might not happen.  The reason I 
liked this protocol is because one can buy an actual manufactured 
device, while others can resort to the Arduino sketch.

>>> So I sat down and wrote an Arduino implementation of that specification just
>>> to see what the performance would be. You can find it at:
>>> https://github.com/axic/dtiic
>> I had a quick look at code and it seems simple, readable and fastest
>> at least to sustain the 400khz mode of i2c.
>>
>> BTW, I'm thinking on making an arduino code compatible with some of
>> the already in kernel driver and i2c-tiny-usb could be a really valid
>> candidate. This way we could only ask for a .ino inclusion in mainline
>> with some sort of documentation on how to cook a homemade I2C over
>> UART bridge.
>
> The only downside of this approach is that we should write something
> USB based, not UART, so it will limit the choice of usable Arduino
> board to only the Leonardo.
> I think we should stick for an serio based driver to be compatible
> with all the boards.
>
> I have no problem in writing such a driver, probably I will look into
> this in the next few days.

Yes, if one can implement any USB device on the Leonardo and not just 
HID that makes it really simple to support i2c-tiny-usb. Or 
i2c-robotfuzz-osif for that matter.

The only current serio-based I2C bus is i2c-taos-evm which isn't even 
full I2C, but smbus. Writing an Arduino sketch for that seems simple 
enough too.

Best,
Alex

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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Bernhard Kraft]

Hi Alex,

On 2015-05-19 14:20, Alex Beregszaszi wrote:

> So I sat down and wrote an Arduino implementation of that specification
> just to see what the performance would be. You can find it at:
> https://github.com/axic/dtiic

I already took a look at the robot-electronics.co.uk link yesterday. I 
wasn't very fond of the serial protocol. It seems they implemented some 
kind of timeout which determines the start and end of a message.

Quote:
http://www.robot-electronics.co.uk/htm/usb_iss_i2c_tech.htm
"A gap will result in the USB-ISS re-starting its internal command 
synchronization loop and ignoring the message."


Hence my implementation uses <ESC> as ERROR character. Whenever one of 
the devices PC/Arduino looses sync or notices another problem it sends 
an <ESC> on to the serial line (0x1B). The <ESC> character is even valid 
through data transfers. This requires a literal <ESC> character to get 
escaped somehow. For this reason I introduced a quoting character 
(indeed it is an escape character - maybe I should use another character 
than <ESC> for signaling an error). The quoting character (currently 
'\') can quote itself and the <ESC> character. Every other combination 
of '\' and another character is invalid and causes the other end to send 
<ESC>
(error).

I don't know if this protocol is clever but it can get implemented using 
a layered approach and synchronization can get achieved without the need 
of other lines. Using the escaped mechanism also software flow control 
like XON/XOFF could get implemented:
http://en.wikipedia.org/wiki/Software_flow_control
(I didn't knew Xon was a Star Trek character :)

Here a link to my current Arduino sketch:
https://gist.github.com/kraftb/8c0bbcc35a9778608d74

I think to create a nice and useful sketch the communication would have 
to get a layer for supporting different client side (Arduino) features 
(I2C, SPI, GPIO).



Is it a problem that we discuss this issue here? I see mostly patches 
going around. If someone feels annoyed please post and we move to some 
other list.


greetings,
Bernhard
-- 
Wer nicht gelegentlich auch einmal kausalwidrige Dinge zu denken vermag,
wird seine Wissenschaft nie um eine neue Idee bereichern können.
Max Planck (1858-1947)
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Re: [RFC] Driver for Arduino-as-I2C-adapter

[Alex Beregszaszi]

Hi,

Bernhard Kraft wrote:
> Hi Alex,
>
> On 2015-05-19 14:20, Alex Beregszaszi wrote:
>
>> So I sat down and wrote an Arduino implementation of that specification
>> just to see what the performance would be. You can find it at:
>> https://github.com/axic/dtiic
>
> I already took a look at the robot-electronics.co.uk link yesterday. I 
> wasn't very fond of the serial protocol. It seems they implemented 
> some kind of timeout which determines the start and end of a message.
>
> Quote:
> http://www.robot-electronics.co.uk/htm/usb_iss_i2c_tech.htm
> "A gap will result in the USB-ISS re-starting its internal command 
> synchronization loop and ignoring the message."
>
>
> Hence my implementation uses <ESC> as ERROR character. Whenever one of 
> the devices PC/Arduino looses sync or notices another problem it sends 
> an <ESC> on to the serial line (0x1B). The <ESC> character is even 
> valid through data transfers. This requires a literal <ESC> character 
> to get escaped somehow. For this reason I introduced a quoting 
> character (indeed it is an escape character - maybe I should use 
> another character than <ESC> for signaling an error). The quoting 
> character (currently '\') can quote itself and the <ESC> character. 
> Every other combination of '\' and another character is invalid and 
> causes the other end to send <ESC>
> (error).

Common way for escaping is to choose the least frequent character as an 
escape character and if it needs to be represented as a vanilla value, 
use double escaping for that. E.g. in your example <ESC> is escaping and 
<ESC><ESC> represents data.

> I think to create a nice and useful sketch the communication would 
> have to get a layer for supporting different client side (Arduino) 
> features (I2C, SPI, GPIO).

I know you don't like the USB-ISS (and I am not 100% happy with it 
either), but that does support I2C, SPI, GPIO and UART.

Best,
Alex

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