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clarification about I2C

borquee

December 04, 2024 10:26

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I'm trying to make my own controller and I need RPI to be I2C slave

As I see... there are I2Cs on GPIO2-3 (with something on 0x60) and on GPIO0-1 (second defined in config.txt but there is nothing on it, master also?)

Since there is nothing on the second is it safe to use it for my own stuff? or do I have create new one on (let's say) GPIO5-6 or somewhere else?

 

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7 comments

• 0
  
  HiFiBerry team December 04, 2024 13:42

  GPIO0/1 are reserved for HAT EEPROM and should not be used for any other hardware. I2C on GPIO2/3 runs as master for almost all of our sound cards. You can't use this as an I2C slave. The best way is probably to implement your I2C slave in software using bit-banging. 

• 0
  
  borquee December 04, 2024 14:09

  I've set it on GPIO12/13 ... but I'm having trouble turning it to slave mode... any code snippet would be helpfull

   

• 0
  
  borquee December 04, 2024 15:14

  so far ... config.txt

  dtoverlay=i2c-gpio,bus=4,i2c_gpio_sda=12,i2c_gpio_scl=13

  code:

  self.i2c_address=0x30   # Slave address

  self.busNum=4       # Bus number

  self.gpio=pigpio.pi()

  if not self.gpio.connected:

       raiseRuntimeError("Failed to connect to pigpio daemon.")

   

  # Set up the I²C slave

  self.handle=self.gpio.i2c_open(self.busNum, self.i2c_address)

  
  

  # Register a callback for incoming data

  self.callback=self.gpio.event_callback(pigpio.EVENT_BSC, self._callback)

  
  

  logging.info(f"I2C slave initialized at address 0x{self.i2c_address:X} on bus {self.busNum}.")

  ------------

  # i2cdetect -y 4

       0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f

  00:                         -- -- -- -- -- -- -- --

  10: -- -- -- -- 14 -- -- -- -- -- -- -- -- -- -- --

  20: 20 -- 22 -- -- -- -- -- -- -- -- -- -- -- -- --

  30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

  40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

  50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

  60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

  70: -- -- -- -- -- -- -- --                         

   

  it's not there but it can see all other slaves, so something works (also esp32 sees all those slaves at the same time)

   

   

   

   

   

   

   

   

   

   

   

   

   

   
• 0
  
  HiFiBerry team December 04, 2024 15:18

  i2cdetect sets the interface to master mode (otherwise you would not be able to scan the bus). You can't run an interface as I2C master and slave at the same time.

• 0
  
  borquee December 04, 2024 15:24

  ok... reboot... did nothing on rpi

  on esp32 side (does scanning on loop)

  16:22:51.220 -> Scanning complete.
  16:22:54.223 -> Scanning for I2C devices...
  16:22:54.223 -> I2C device found at address 0x14
  16:22:54.223 -> I2C device found at address 0x20
  16:22:54.223 -> I2C device found at address 0x22

   

• 0
  
  borquee December 05, 2024 10:39

  So... theoretically ... in order to connect two i2c devices that want to be masters I have to make a "bridge" that runs as a slave on both i2c lines ... nice 

• 0
  
  HiFiBerry team December 05, 2024 18:51

  Yes, I2C is designed for a single master. There is no collision-detection. Therefore multiple masters will mess up stuff.
  There can be only one master on an I2C bus.