Python Spidev

This project contains a python module for interfacing with SPI devices from user space via the spidev linux kernel driver.

This is a modified version of the code originally found here

All code is GPLv2 licensed unless explicitly stated otherwise.

More Details on Use with the Omega2

See more details here:

• https://onion.io/2bt-brand-new-os-release/#spiimprovement
• http://community.onion.io/topic/3179/spi-bus-in-python/17

Installation on Omega2

The spidev module is available for Python2 and Python3, the installation commands are slightly different.

Connect to the Omega's command line and run the following commands to install the Python2 module:

opkg update
opkg install python-light python-spidev

---

To install the Python3 module, run this set of commands

opkg update
opkg install python3-light python3-spidev

Usage

import spidev
spi = spidev.SpiDev()
spi.open(bus, device)
to_send = [0x01, 0x02, 0x03]
spi.xfer(to_send)

Settings

import spidev
spi = spidev.SpiDev()
spi.open(bus, device)

# Settings (for example)
spi.max_speed_hz = 5000
spi.mode = 0b01

...

• bits_per_word
• cshigh
• loop - Set the "SPI_LOOP" flag to enable loopback mode
• no_cs - Set the "SPI_NO_CS" flag to disable use of the chip select (although the driver may still own the CS pin)
• lsbfirst
• max_speed_hz
• mode - SPI mode as two bit pattern of clock polarity and phase [CPOL|CPHA], min: 0b00 = 0, max: 0b11 = 3
• threewire - SI/SO signals shared

Methods

Connects to the specified SPI device, opening /dev/spidev<bus>.<device>

open(bus, device)

---

Read n bytes from SPI device. Returns list of bytes read by SPI controller

readbytes(n)

---

Writes a list of values to SPI device.

writebytes(list of values)

---

Performs an SPI transaction. Chip-select should be released and reactivated between blocks. Delay specifies the delay in usec between blocks. Returns list of bytes read by SPI controller.

xfer(list of values[, speed_hz, delay_usec, bits_per_word])

---

Performs an SPI transaction. Chip-select should be held active between blocks. Returns list of bytes read by SPI controller.

xfer2(list of values[, speed_hz, delay_usec, bits_per_word])

---

Disconnects from the SPI device.

close()

---

Half-Duplex Transmissions

Performs a half-duplex SPI transaction. Chip-select should be held active between blocks. Returns list of bytes read by SPI controller.

Use this function when the intent is to write a number of bytes and then immediately read a number of bytes (register reads for example)

xfer3(list of values to be written, number of bytes to read [, speed_hz, delay_usec, bits_per_word])