Hello,

 

I have a 4x20 LCD display (with an HD44780 compatible adaptor) connected to my Banana Pi. It is running (freshly installed, switched from Bananian) on the mainline kernel:

Linux bpi 4.9.7-sunxi #1 SMP Thu Feb 2 01:52:06 CET 2017 armv7l GNU/Linux

However, the display is not recognized. I checked the wire connections multiple times, they're okay and the backlight is on.

 

So I assume this is a software issue. The output of "i2cdetect -y 1" is:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --                         

which leads me to the consideration that it is not even recognized by the system.

 

I did the following things - without success:

• run "apt-get dist-upgrade" (where some 404 errors occured, see this topic for details)
• installed "i2c-tools" and "python-smbus"
• loaded "i2c-dev" kernel module

 

According to the documentation https://docs.armbian.com/Hardware_Allwinner/#connect-your-lcd-display, the I2C stuff should work out of the box in the mainline kernel.

 

Any help would be appreciated.

 

Best regards and thanks in advance,

Norbert Kahl

Which BananaPi are you using ?

Because maybe you are not looking at the right I2C bus, did you look at other buses ?

On A20_BananaPi, the I2C on the header is /dev/i2c-3 (i2c-1 is the camera).

 

I am using a "normal" Banana Pi, not a Pro or M2 model.

 

There are two I2C-busses here:

root@bpi:/dev# ls /dev/i2c-*
/dev/i2c-0  /dev/i2c-1

On the 0-bus, there is "something" detected but I guess it belongs to the system or internal hardware, not to the display:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- UU -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- -- 

The 1-bus is just blank.

Yes, I2C-0 has the PMIC attached to it.

Since you don't see the i2c-3, it is probably not enabled in the DT, you will have to tweak it by decompile the DTB, edit it, and recompile it. (Of course, after having done a backup of the previous one)

 

Sorry for all the rush. It was the length of the cable (> 2 metres) which caused this error, since pull-up resistors and terminators are required at that length. Just another I2C-Newbie...

 

When using jumper wire (~ 20cm), it works, the LCD display appears as 0x27 on I2C-1.

 

Thanks for all the help!

 

Best regards,

Norbert Kahl

Ah ! Of course, PullUps are required. Some boards have them on board, some others don't.

 

Yep, and with the pull-up resistors, everything works fine now.