Loopback Example Using GPIO5

Using the functions listed above it is easy to implement the loopback example given earlier:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "Gpio5.h"
int main(int argc, char **argv)
{
    rp1_Init();
    gpio_set_function(8, GPIO_FUNC_SPI);  // CS0
    gpio_set_function(7, GPIO_FUNC_SPI);  // CS1
    gpio_set_function(3, GPIO_FUNC_SPI);  // CS2
    gpio_set_function(4, GPIO_FUNC_SPI);  // CS3
    gpio_set_function(9, GPIO_FUNC_SPI);  // MISO
    gpio_set_function(10, GPIO_FUNC_SPI); // MOSI
    gpio_set_function(11, GPIO_FUNC_SPI); // SCLK
    spi_init(SPI0, 5000000);
    spi_set_format(SPI0, 8, SPI_CPOL_0, SPI_CPHA_0,
                                       SPI_MSB_FIRST);
    spi_set_slave(SPI0, 0);
    uint8_t wBuff[1] = {0xAA};
    uint8_t rBuff[1];
    int n = spi_write_read_blocking(
                               SPI0, wBuff, rBuff, 1);
    printf(" %X %X %d \n ", wBuff[0], rBuff[0], n);
    return (EXIT_SUCCESS);
}

Notice that we set all of the CS lines that SPI0 supports but only use CS0. We could include the setting up of the GPIO lines in the spi_init function, but doing it this way allows the selection of which CS lines to initialize within the user program.

In chapter but not in this extract

• The MCP3008
• Connecting to the Pi
• Basic Configuration
• The Protocol
• MCP3008 in Gpio5
• How Fast
• The MCP3008 Driver 
• Problems

Summary

• The Pi 5 has six SPI controllers but not all can be used at the same time.

• Making SPI work with any particular device has four steps:

1. Discover how to connect the device to the SPI pins. This is a matter of identifying pinouts and what chip selects are supported.

2. Find out how to configure the Pi's SPI bus to work with the device. This is mostly a matter of clock speed and mode.

3. Identify the commands that you need to send to the device to get it to do something and what data it sends back as a response.

4. Find, or work out, the relationship between the raw reading, the voltage, and the quantity the voltage represents.

• The Linux SPI driver can be used to interface to any SPI device as long as you know what commands to send and what the data sent back means.

• The SPI driver is supported by the SPIdev header which provides the basic tools to work with the ioctl interface.

• The SPI driver uses general GPIO lines as chip select lines and not the built-in hardware.

• The hardware SPI controllers are based on Synopsys DW_apb_ssi and this is well documented.

• It is easy to extend Gpio5 to work with SPI with many advantages.

• Using the other SPI interfaces on the Pi 5 is just a matter of selecting the appropriate driver.

• The MCP3000 range of A-to-D converters is very easy to use via SPI. It can be used directly from the SPI bus by sending commands and reading the data generated.

• There is also a specific MCP3008 driver which allows you to work with the device without having to know anything about SPI or the commands that have to be sent to read the data.

• The MCP3008 driver is an example of an IIO device.

You can find the complete Gpio5 at its Github repo:

 https://github.com/IOPress/Gpio5,

at the book’s web page:

https://iopress.info/index.php/books/raspberry-pi-5-iot-in-c

Raspberry Pi 5 IoT In C
Drivers and Gpio5

By Harry Fairhead

Buy from Amazon.

Contents

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

 <ASIN:1871962943>

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