spitarget – Serial Peripheral Interface protocol target
The spitarget module contains classes to support an SPI target.
Example that emulates an SPI analog-to-digital converter:
import board
import analogio
from spitarget import SPITarget
ain0 = analogio.AnalogIn(board.A0)
ain1 = analogio.AnalogIn(board.A1)
selected_channel = ain0
def map_adc_channel(index):
return ain0 if (index == 0) else ain1
mosi_buffer = bytearray(2)
miso_buffer = bytearray(2)
with SPITarget(sck=board.D12, mosi=board.D13, miso=board.D11, ss=board.D10) as device:
while True:
# Convert analog signal to array of bytes
reading = selected_channel.value
miso_buffer[0] = (reading >> 8) & 0xFF
miso_buffer[1] = (reading) & 0xFF
# Send array of bytes over SPI to main
device.load_packet(mosi_buffer, miso_buffer)
while not device.wait_transfer(timeout=-1):
pass
# Handle command from main, which sets the ADC channel
selected_channel = map_adc_channel((mosi_buffer[0] << 8) | mosi_buffer[1])
Communicating with the ADC emulator from the REPL of an attached CircuitPython board might look like
>>> import board
>>> import digitalio
>>> import busio
>>> import time
>>>
>>> ## setup
>>> spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
>>> cs = digitalio.DigitalInOut(board.CS)
>>> cs.direction = digitalio.Direction.OUTPUT
>>> cs.value = True
>>> spi.try_lock()
True
>>>
>>> ## ADC command: read from A0
>>> cs.value = False
>>> spi.write(bytearray([0, 0]))
>>> cs.value = True
>>>
>>> # wait for ADC to read a value
>>>
>>> ## get two-byte output from ADC
>>> adc_result = bytearray(2)
>>> cs.value = False
>>> spi.readinto(adc_result, write_value=1)
>>> cs.value = True
>>> list(adc_result)
[0, 255]
Available on these boards
- class spitarget.SPITarget(sck: microcontroller.Pin, mosi: microcontroller.Pin, miso: microcontroller.Pin, ss: microcontroller.Pin)
Serial Peripheral Interface protocol target
SPI is a four-wire protocol for communicating between devices. This implements the secondary (aka target or peripheral) side.
- Parameters:
- __exit__() None
Automatically deinitializes the hardware on context exit. See Lifetime and ContextManagers for more info.