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.
Available on these boards
- 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
- __enter__() I2CPeripheral¶
No-op used in Context Managers.
- __exit__() None¶
Automatically deinitializes the hardware on context exit. See Lifetime and ContextManagers for more info.
- request(timeout: float = -1) I2CPeripheralRequest¶
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
- class i2cperipheral.I2CPeripheralRequest(peripheral: 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__() I2CPeripheralRequest¶
No-op used in Context Managers.
- read(n: int = -1, ack: bool = True) bytearray¶
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(buffer: circuitpython_typing.ReadableBuffer) int¶
Write the data contained in buffer.
- Parameters
buffer (ReadableBuffer) – Write out the data in this buffer
- Returns
Number of bytes written
- ack(ack: bool = True) None¶
Acknowledge or Not Acknowledge last byte received. Use together with
I2CPeripheralRequest.read()ack=False.- Parameters
ack – Whether to send an ACK or NACK