i2cperipheral – Two wire serial protocol peripheral

The i2cperipheral module contains classes to support an I2C peripheral.

Example emulating a peripheral with 2 addresses (read and write):

import board
from i2cperipheral import I2CPeripheral

regs = [0] * 16
index = 0

with I2CPeripheral(board.SCL, board.SDA, (0x40, 0x41)) as device:
    while True:
        r = device.request()
        if not r:
            # Maybe do some housekeeping
            continue
        with r:  # Closes the transfer if necessary by sending a NACK or feeding dummy bytes
            if r.address == 0x40:
                if not r.is_read:  # Main write which is Selected read
                    b = r.read(1)
                    if not b or b[0] > 15:
                        break
                    index = b[0]
                    b = r.read(1)
                    if b:
                        regs[index] = b[0]
                elif r.is_restart:  # Combined transfer: This is the Main read message
                    n = r.write(bytes([regs[index]]))
                #else:
                    # A read transfer is not supported in this example
                    # If the microcontroller tries, it will get 0xff byte(s) by the ctx manager (r.close())
            elif r.address == 0x41:
                if not r.is_read:
                    b = r.read(1)
                    if b and b[0] == 0xde:
                        # do something
                        pass

This example sets up an I2C device that can be accessed from Linux like this:

$ i2cget -y 1 0x40 0x01
0x00
$ i2cset -y 1 0x40 0x01 0xaa
$ i2cget -y 1 0x40 0x01
0xaa

Warning

I2CPeripheral makes use of clock stretching in order to slow down the host. Make sure the I2C host supports this.

Raspberry Pi in particular does not support this with its I2C hw block. This can be worked around by using the i2c-gpio bit banging driver. Since the RPi firmware uses the hw i2c, it’s not possible to emulate a HAT eeprom.

class i2cperipheral.I2CPeripheral(scl: microcontroller.Pin, sda: microcontroller.Pin, addresses: Sequence[int], smbus: bool = False)

Two wire serial protocol peripheral

I2C is a two-wire protocol for communicating between devices. This implements the peripheral (sensor, secondary) side.

Parameters:
  • scl (Pin) – The clock pin
  • sda (Pin) – The data pin
  • addresses (list[int]) – The I2C addresses to respond to (how many is hw dependent).
  • smbus (bool) – Use SMBUS timings if the hardware supports it
deinit(self)

Releases control of the underlying hardware so other classes can use it.

__enter__(self)

No-op used in Context Managers.

__exit__(self)

Automatically deinitializes the hardware on context exit. See Lifetime and ContextManagers for more info.

request(self, timeout: float = -1)

Wait for an I2C request.

Parameters:timeout (float) – Timeout in seconds. Zero means wait forever, a negative value means check once
Returns:I2C Slave Request or None if timeout=-1 and there’s no request
Return type:I2CPeripheralRequest
class i2cperipheral.I2CPeripheralRequest(peripheral: i2cperipheral.I2CPeripheral, address: int, is_read: bool, is_restart: bool)

Information about an I2C transfer request This cannot be instantiated directly, but is returned by I2CPeripheral.request().

Parameters:
  • peripheral – The I2CPeripheral object receiving this request
  • address – I2C address
  • is_read – True if the main peripheral is requesting data
  • is_restart – Repeated Start Condition
address :int

The I2C address of the request.

is_read :bool

The I2C main controller is reading from this peripheral.

is_restart :bool

Is Repeated Start Condition.

__enter__(self)

No-op used in Context Managers.

__exit__(self)

Close the request.

read(self, n: int = -1, ack: bool = True)

Read data. If ack=False, the caller is responsible for calling I2CPeripheralRequest.ack().

Parameters:
  • n – Number of bytes to read (negative means all)
  • ack – Whether or not to send an ACK after the n’th byte
Returns:

Bytes read

write(self, buffer: ReadableBuffer)

Write the data contained in buffer.

Parameters:buffer (ReadableBuffer) – Write out the data in this buffer
Returns:Number of bytes written
ack(self, ack: bool = True)

Acknowledge or Not Acknowledge last byte received. Use together with I2CPeripheralRequest.read() ack=False.

Parameters:ack – Whether to send an ACK or NACK