This is the python script I'm running on all the RaspberryPis.Īs you see, I've used an exception to catch possible conflicts on the bus in this multimaster setup. I like to share here my code, I think it can be helful to understand what I'm doing. On the RaspberryPis I've used the smbus subset (as shown here).

It worked well: all the machines seems to be pretty much syncronized. I had the single Arduino continuously asked for information on the I2C bus from 6 RaspberryPis.

Any difference between the line state compared to the expected state should be treated as a collision and the master immediately back off and retry later, which should leave the other talking master to complete the transaction without error.Īctually, even if my hardware/electrical configuration is quite technically incorrect, I've been able to make it continuously work (the most I could keep it runnign was 4/5 hours approx). If a master supports a multiple master configuration then it has to read back SDA whenever it is transmitting, and support clock stretching.

Here the interested lines of code for twi_init():Īctually that is supported by the i2c spec, but admittedly not on the Pi implementation. See the begin and the end functions (inside the Wire.cpp file) which in turns call the twi_init() and twi_disable() functions (see utility/twi.c file). On the Arduino side, I know pins A4 (SDA) and A5 (SCL) already have their own internal pullups, or at least that's what I can say after reading the source code of the Wire library I'm using for the Arduino code. Do these (I2C 0) RaspberryPi pins already have their own internal pullup resistors? Just in case, can these resistors be enabled/disabled? The problem here is that Arduino and the PIs are operating at two different voltages (isn't it?).Īs suggested by the same sparkfun tutorial, in cases like this I can use the 'trick' of putting the pullups on the lower voltage device (the RaspberryPi in my case).ġ. I know that the I2C bus drivers are “open drain”, so I must take care for the signal to return high when not in use.

My question is about the pullup resistors. Config1.jpg (33.96 KiB) Viewed 6246 times

Arduino pull up resistor wire library