The CM5 has SPI and you can use it via Linux drivers or directly.  In this article we look at how to use it via a driver. This is an extract from the newly-published Raspberry Pi Compute Module 5 IoT In C

Raspberry Pi Compute Module 5
IoT In C
Using Linux Drivers and Gpio5

By Harry Fairhead

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Contents

1. The CM5 For The IoT
2. Setting Up the CM5
3. C and Visual Studio Code
4. Drivers: A First Program
5. The GPIO Character Drive
6. GPIO Using I/O Control
7. GPIO Events
8. GPIO Hardware With Gpio5 
         Extract:  GPIO Registers 
9. Some Electronics
10. The Device Tree
11. Pulse Width Modulation
         Extract: PWM Using GPIO5
12. SPI Devices
         Extract: Getting Started With SPI ***NEW!!!
13. I2C Driver and Gpio5
14. Sensor Drivers – Linux IIO & hwmon
15. 1-Wire Bus
16. The PIO
         Extract: Getting Started With PIO
17. Going Further With Drivers
18. Almost Real-Time Linux
19. Appendix I Gpio5

 <ASIN:1871962951> 

SPI Devices

The CM5 offers two standard ways of connecting more sophisticated devices in hardware – the Serial Peripheral Interface or SPI bus and the I2C or I-⁠squared-C bus. In addition there is a Linux driver which supports the non-standard 1-Wire bus in software. The following chapters focus on these buses rather than specific devices. The advantage of a bus is that, once you know how to use it, connecting compatible devices is more or less the same task, irrespective of device.

There are drivers for some specific SPI devices and if such a driver exists you should use it. More information on how to do this is given later. However, if a driver doesn’t exist it isn’t difficult to interface to an SPI device at a lower level via the Linux SPI driver. First, however, we need to know something about how SPI works. If you just want to use a device driver, skip this section until you need it.

SPI Bus Basics

In the hardware configuration most used for the Pi, there is a single master and, at most, two slaves.

The signal lines are:

• MOSI (Master Output Slave Input), i.e. data to the slave

• MISO (Master Input Slave Output), i.e. data to the master

• 
  SCLK (Serial Clock), which is always generated by the master

In general, there can also be any number of SS (Slave Select), CE (Chip Enable) or CS (Chip Select) lines, which are usually set low to select which slave is being addressed. Notice that unlike other buses, I2C for example, there are no SPI standard commands or addresses, only bytes of data. However, slave devices do interpret some of the data as commands to do something or send some particular data.

SPI Interfaces

The CM5 has six SPI interfaces that can be accessed via the exposed GPIO lines.

Notice that some SPI controllers share GPIO lines and therefore cannot be used at the same time, e.g SPI2 and SPI3, SPI4 and SPI0. For these and other reasons it is better to use SPI0 and SPI1 if at all possible.