SPI0 uses GPIO7-11 and is found on all rPi’s to date.
It has two CS lines – 0 and 1 – allowing control 2 devices natively. It is also possible to run the SPI module without a CS line – i.e. enabling the use of any free GPIO pin as a manual CS line.
It supports clock speeds of 8kHz to 125mHz.
The device reports supporting the following Linux SPIdev options:
- SPI_CS_HIGH (CS inverted)
- SPI_3WIRE (MOSI & MISO share the same line)
- SPI_NO_CS (Device is signalled elsewhere)
- Arch requires Prerequisite Configuration. See this page for more information.
Add the following to enable SPI0
The module is called spi_bcm2835. There is an older module called spi_bcm2708 which amongst other things only supports clock frequencies in powers of 2. See here for a discussion: https://www.raspberrypi.org/forums/viewtopic.php?f=44&t=43442&p=347073
If SPI0 is enabled in the config.txt the kernel module should load automatically after a reboot. Check with lsmod.
$ lsmod | grep spi spi_bcm2835 7216 0
If it doesn’t appear make sure this isn’t blacklisted in/etc/modprobe.d/raspi-blacklist.conf. When the module is running you will find two device nodes have been created.
crw-rw---- 1 root spi 153, 0 Jan 11 15:47 spidev0.0 crw-rw---- 1 root spi 153, 1 Jan 11 15:47 spidev0.1
There is one device per CS line
You should already have a user group called ‘spi’ which has read/write access to the device nodes. Add yourself and any other accounts that need access to this group if you have not already done so.
sudo usermod -a -G spi <acccount>
Despite the Broadcom 2835 ARM Peripherals document (p150) discussing multiple transfer sizes including 9bit ‘Lossi’ – commonly used by LCD screens – however when the device is queried it only supports 8bit transfers. This is a real pity. Perhaps someone can explain that to me.