How to test the i2c

Android or Linux ?  If Linux, 3.0.35 or 3.15-rc* ?

Which i2c interface on which expansion port ?  There are four i2c interfaces, some are available on multiple expansion interfaces, some expansion interfaces have multiple i2c interfaces available.

For example, if you're talking about J13 then there's both i2c3 & i2c4.  The physical i2c interfaces don't necessarily map directly to the /dev entries.. So you can have things like /dev/i2c-2 maps to the physical i2c4 pins..

However you look at it, you need more information to be able to work out what you need to do.

Under Linux, you should look for the i2c-tools package. You'll want i2c-detect or i2c-dump to do the i2c accesses.

I don't use android, so can't really help much if that's what you're trying to use.

Ah ok ok, What i want to do is to test the i2c interface but right now i don´t have any i2c device to interface with so i´m thinking just sending data over the i2c3 interface and check the signals with a logic analyzer.

I will do it on linux and yes, as you said is the J13 , i2c3 (pin 31 and 33) which is on /dev/i2c-2.

I already read something about i2c-tools but the thing is that i´m not connecting any device on the port therefore using i2c-detect doesn´t get me any address and i can´t use i2cdump because i don´t know in what address to write data.

For example when i tested the uart i send the data without the need of connecting anything and i just check the signals with the logic analyzer, i´m new at this and i don´t know how to do that with the i2c interface.

You may not be able to use the physical i2c3. The reason is that i2c3_sda is likely to be used for the ethernet interrupt workaround.  i2c4 might be a better choice, depending on which kernel you're using.

i2cdetect probes a range of addresses, so if you connect the scope, you'll see it trying every address with no response.

Similarly, with i2cdump you can ask it to dump a range of data from a particular address. If you don't have anything connected, it won't matter which address you pick, you won't get any data returned, but you will be able to see the attempts to read the data on the scope, something like this:

closer in it looks like this

As you can see the address is clocked out, but no ack from the non-existent device, so we just loop sending addresses.

The above was done with i2cdetect with nothing on the bus, the output from i2cdetect looks like this:

root@riotboard:~# i2cdetect 2
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-2.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                        

With my kernel, /dev/i2c-2 is i2c4 on pins 35 & 37 on J13

If you have a monitor connected to HDMI then you can read it's EDID with something like

root@riotboard:~# i2cdump 1 0x50
No size specified (using byte-data access)
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-1, address 0x50, mode byte
Continue? [Y/n] y
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
00: 00 ff ff ff ff ff ff 00 10 ac 21 a0 53 35 44 30    ........??!?S5D0
10: 16 10 01 03 80 29 1f 78 ee ee 91 a3 54 4c 99 26    ?????)?x????TL?&
20: 0f 50 54 a5 4b 00 81 80 a9 40 71 4f 01 01 01 01    ?PT?K.???@qO????

Thanks !!, it works and also you´re explanation was really helpful, .

Thanks !!, it works and also you´re explanation was really helpful, .