HowTo: GPIO access, I2C, Kernel Building

Developers
1

Hi, it’s Paul again :wink:

Intro

I found some time over the last days to play with the GPIOs and I2C. And got all of them to work, as well as I2C support:

00-i2c-setup
00-i2c-setup4032×3024 3.32 MB 

    WARNING! This program can confuse your I2C bus, cause data loss and worse!
    I will probe file /dev/i2c-0.
    I will probe address range 0x03-0x77.
    Continue? [Y/n] 
        0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
    00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
    10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- -- 
    40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
    70: -- -- -- -- -- -- 76 --

The GPIOs worked out of the box. I2C was a bit tricky (especially if you know nothing about linux kernel development, kind of like me)

GPIOs

This section describes how to use the pins via the sysfs interface.

Create the pin’s interface:

echo 32 > /sys/class/gpio/export # PB0, green cable

which creates the interface’s pin directory:

cd /sys/class/gpio/gpio32/

Which contains the following files

active_low  device  direction  edge  power  subsystem  uevent  value

To use this pin as an output pint you can configure it

echo out > /sys/class/gpio/gpio32/direction

And enable it

echo 1 > /sys/class/gpio/gpio32/value

Or disable it

echo 0 > /sys/class/gpio/gpio32/value

Short version for I2C (Setup)

If you mount /dev/mmcblk0p1 /mnt/boot/ you will find a file sun8i-r16-clockworkpi-cpi3.dtb which is missing the entry (in it’s original source form)

&i2c1 {
	status = "okay";
};

Which I rebuilt using the kernel sources version 5.2-rc4.
I replaced the file (and the Kernel with my rebuilt kernel). And then got the device /dev/i2c-0 after a reboot.

Details for I2C

I wrote the long version down while figuring things out on my blog (it’s a bit much for a forum post):

p3dt.net/post/2019/12/26/gameshell-gpios.html

Let me know if this helps or if you have any questions :slight_smile:

Resulting Kernel/DeviceTree files for I2C

If you don’t want to build everything yourself you can download my kernel and the accompanying files here:

https://p3dt.net/assets/downloads/cpi-0.4-kernel-5.2-rc4-i2c.tar.gz
Using these files is at your own risk, if you run into issues, I will do my best to answer your questions in this thread.

You need to replace these (make backups first!) on the boot partition.
Note: It might be the case that replacing the .dtb file is sufficient if you have a different kernel, but I haven’t tested this. If you are up for some tests, try this first and let us know, thank you.

Have fun,
Paul

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2

The GPIO Table is as follows:

Type Pin # (ext.) Pin # (Package) Function 1 Function 2 Pin # (sysfs) Color
3V0 1 blue
GPIO 2 PB0 UART0/2_TX PB-EINT0 32 green
GPIO 3 PB1 UART0/2_RX PB-EINT1 33 yellow
GND 4 white
GPIO 5 PH5 I2C1-SDA 229 red
GPIO 6 PH4 I2C1-SCL 228 brown
GND 7 black
GPIO 8 PH6 UART3-TX SPI0-CS 230 blue
GPIO 9 PH7 UART3-RX SPI0-CLK 231 green
GPIO 10 PH9 UART3-CTS SPI0-MISO 233 yellow
GPIO 11 PH8 UART3-RTS SPI0-MOSI 232 white
GND 12 red
5V0 13 brown
5V0 14 black

This should give you an orientation:
03-on.sm

3 Likes
3

OMG you made it!!!

I am being occupied by other projects hence no bandwidth for me to follow up on this topic…

just a quick question: What did you changed in kernel for enable I2C support? - Pardon me, just found it recorded in your blog.

I may not able to use your kernel because of mine is customized as well, so I need to figure out what has been changed.

My blueprint is integrate CPI with a CO2 sensor / PM2.5 sensor, seems we got a chance to make it works by some effort.

4

try with exchanging only the dtb file, leave your kernel as is. in theory this should work to. as long as the i2c support is already built in which should be