piPython 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.

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

open(bus, device)

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

readbytes(n)

Read n bytes from SPI device, returning a list of integers.

readbytesb(n)

Read n bytes from SPI device, returning an (immutable) bytes object (more efficient for larger transfers).

readbuffer(buffer [, length [, offset]])

Read length bytes from SPI device into an existing bytearray object at the given offset (single SPI transfer) If length is not specified or 0, tries to read to the end of the buffer. If offset is not specified, default is 0.

writebytes(list of values)

Writes a list of values to SPI device.

writebytes2(list of values)

Similar to writebytes but accepts arbitrary large lists. If list size exceeds buffer size (which is read from /sys/module/spidev/parameters/bufsiz), data will be split into smaller chunks and sent in multiple operations.

Also, writebytes2 understands buffer protocol so it can accept numpy byte arrays for example without need to convert them with tolist() first. This offers much better performance where you need to transfer frames to SPI-connected displays for instance.

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

Performs an SPI transaction. Chip-select should be released and reactivated between blocks. Delay specifies the delay in usec between blocks.

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

Performs an SPI transaction. Chip-select should be held active between blocks.

xfer3(list of values[, speed_hz, delay_usec, bits_per_word])

Similar to xfer2 but accepts arbitrary large lists. If list size exceeds buffer size (which is read from /sys/module/spidev/parameters/bufsiz), data will be split into smaller chunks and sent in multiple operations.

close()

Disconnects from the SPI device.