View source for How to use VisionSOM-6ULL SPI interface in C programs

{{PageHeader|How to use VisionSOM-6ULL SPI interface in C programs}}

== Configuring device tree to enable I2C interface ==

To enable SPI interface you may need to add (or modify) interface definition, your dts file should contain:

<pre>&ecspi3 {
    fsl,spi-num-chipselects = <1>;
    cs-gpios = <&gpio1 20 0>;
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_spi3>;
    status = "okay";
    spidev@0 {
        compatible = "spidev";
        spi-max-frequency = <1000000>;
        reg = <0>;
    };
};</pre>
Line GPIO1_20 will be used as CS (Chip Select).

In iomux section add or modify SPI pin definition:

<pre>                pinctrl_spi3: spi3grp {
                        fsl,pins= <
                                MX6UL_PAD_UART2_CTS_B__ECSPI3_MOSI      0x100b1
                                MX6UL_PAD_UART2_RX_DATA__ECSPI3_SCLK    0x100b1
                                MX6UL_PAD_UART2_TX_DATA__GPIO1_IO20     0x100b1
                                MX6UL_PAD_UART2_RTS_B__ECSPI3_MISO      0x100b1
                        >;
                };</pre>
                
Those definitions may need modifications depending on which interface and pins you want to use. You can find more informations on customizing device tree in this [[How_to_customize_Debian_9.2_device_tree|tutorial]].
In this example there is used VisionSOM-6ULL, VisionCB-STD and [http://wiki.kamami.pl/index.php?title=Plik:KAmodL3GD20_schemat.png KAmodL3GD20 module with L3GD20 gyroscope]). KAmodL3GD20 module is connected to Raspberry Pi connector on VisionCB-STD:

{| class="wikitable"
! VisionSOM-CB-STD RPi connector pin number
! KAmodL3GD20 pin
|-
|VCC-3V3 
| +3.3V
|-
|GND 
|GND
|-
|UART2-CTS 
|SDA
|-
|UART2-RXD 
|SCL
|-
|UART2-RTS 
|SDO
|-
|UART2-TXD	
|CS
|}
                                                           
                                                           
                                                           
== Using SPI interface in C program ==
            
The program below writes 0xFF to L3GD20 CTRL1 register (address 0x20) in function ''configL3GD20'', then it reads 6 registers (addresses 0x28, 0x29...) to read gyroscope X, Y and Z values in function ''readL3DG20''. Note that if you would use write and read functions instead of ''ioctl(fd, SPI_IOC_MESSAGE(1), &tr)'' the program would not work, because CS line would go high between ''read'' and ''write'' calls.   
                                                           

<pre>#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <linux/spi/spidev.h>
#include <linux/types.h>
#include <stdint.h>
#include <unistd.h>
#include <getopt.h>
#include <sys/ioctl.h>


void handleError(char * msg) {
        printf("Error: %s", msg);
        abort();
}

void configL3GD20(int fd) {
        int result;
        uint8_t tx[] = {0x20, 0xFF};
        uint8_t rx[] = {0, 0, };
        struct spi_ioc_transfer tr = {
                .tx_buf = (unsigned long)tx,
                .rx_buf = (unsigned long)rx,
                .len = 2,
                .delay_usecs = 0,
                .speed_hz = 0,
                .bits_per_word = 0,
        };

        result = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
        if (result == 1)
                handleError("Sending SPI frame failed!");
}


void readL3DG20(int fd, int *x, int *y, int *z) {
        int result;
        uint8_t tx[] = {0x28 | (1<<7) | (1<<6), 0, 0, 0, 0, 0, 0};
        uint8_t rx[] = {0, 0, 0, 0, 0, 0, 0};
        struct spi_ioc_transfer tr = {
                .tx_buf = (unsigned long)tx,
                .rx_buf = (unsigned long)rx,
                .len = 7,
                .delay_usecs = 0,
                .speed_hz = 0,
                .bits_per_word = 0,
        };

        result = ioctl(fd, SPI_IOC_MESSAGE(1), &tr);
        if (result == 1)
                handleError("Sending SPI frame failed!");

        *x = (int)(rx[1] | (rx[2] << 8));
        *y = (int)(rx[3] | (rx[4] << 8));
        *z = (int)(rx[5] | (rx[6] << 8));
}


int main() {
        int fd = open("/dev/spidev2.0", O_RDWR);
        int result;
        static uint8_t mode = SPI_MODE_3;
        static uint32_t speed = 1000000;
        int x, y, z;

        result = ioctl(fd, SPI_IOC_WR_MODE, &mode);
        if (result == -1)
                handleError("Setting SPI mode failed!");

        result = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
        if (result == -1)
                printf("Setting SPI speed failed!");

        if (fd >= 0) {
                configL3GD20(fd);

                readL3DG20(fd, &x, &y, &z);

                printf("x=%5d, y=%5d, z=%5d\n", x, y, z);

                close(fd);
        }
        else printf("open err %d\n", errno);

}</pre>


[[File:Visionsom6-ull-spi-example.jpg|center|VisionSOM-6ULL i.MX6 SPI Example]]