spitarget – Serial Peripheral Interface protocol target — Adafruit CircuitPython 1 documentation (original) (raw)

Adafruit CircuitPython

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

• Adafruit Feather M4 Express
• Adafruit Grand Central M4 Express
• Adafruit ItsyBitsy M4 Express
• Adafruit Matrix Portal M4
• Adafruit Metro M4 Airlift Lite
• Adafruit Metro M4 Express
• Adafruit Monster M4SK
• Adafruit PyPortal
• Adafruit PyPortal Pynt
• Adafruit PyPortal Titano
• Adafruit Trellis M4 Express
• AloriumTech Evo M51
• BDMICRO VINA-D51
• CP32-M4
• Capable Robot Programmable USB Hub
• DynOSSAT-EDU-OBC
• LoC BeR M4 base board
• Mini SAM M4
• P1AM-200
• PewPew M4
• PyCubedv04
• PyCubedv04-MRAM
• PyCubedv05
• PyCubedv05-MRAM
• Robo HAT MM1 M4
• SAM32v26
• Seeeduino Wio Terminal
• SparkFun MicroMod SAMD51 Processor
• SparkFun Thing Plus - SAMD51
• Sprite_v2b
• The Open Book Feather
• Winterbloom Sol

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:

• sck (Pin) – The SPI clock pin
• mosi (Pin) – The pin transferring data from the main to the secondary
• miso (Pin) – The pin transferring data from the secondary to the main
• ss (Pin) – The secondary selection pin

deinit() → None

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

__enter__() → SPITarget

No-op used in Context Managers.

__exit__() → None

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

load_packet(mosi_packet: bytearray, miso_packet: bytearray) → None

Queue data for the next SPI transfer from the main device. If a packet has already been queued for this SPI bus but has not yet been transferred, an error will be raised.

Parameters:

• miso_packet (bytearray) – Packet data to be sent from secondary to main on next request.
• mosi_packet (bytearray) – Packet to be filled with data from main on next request.

wait_transfer(*, timeout: float = -1) → bool

Wait for an SPI transfer from the main device.

Parameters:

timeout (float) – Timeout in seconds. Zero means wait forever, a negative value means check once

Returns:

True if the transfer is complete, or False if no response received before the timeout