The NXP i.MX6UL CPU has four SPI buses.
On the ConnectCore 6UL system-on-module:
-
All four SPI ports are available (multiplexed with other functionality)
On the ConnectCore 6UL SBC Express:
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SPI3 port is available at the expansion header
On the ConnectCore 6UL SBC Pro:
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SPI1 port is available at SPI connector
Kernel configuration
You can manage the SPI driver support through the kernel configuration option:
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Freescale i.MX SPI controllers interface (CONFIG_SPI_IMX)
This option is enabled as built-in on the default ConnectCore 6UL kernel configuration file.
Kernel driver
The driver for the SPI interface is located at:
| File | Description |
|---|---|
SPI driver |
Device tree bindings and customization
The i.MX6UL SPI interface device tree binding is documented at Documentation/devicetree/bindings/spi/fsl-imx-cspi.txt.
The common i.MX6UL CPU device tree defines all the SPI ports. The platform device tree must:
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Enable the required SPI port, by setting the status property to okay.
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Choose the GPIOs that will work as chip select lines using property cs-gpios.
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Configure the IOMUX of the pads that will work as SPI port plus the GPIOs to be used as chip select lines.
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Add the spi slave devices as children of the SPI bus node.
Example: SPI1 port (as master) on the ConnectCore 6UL SBC Pro
/* ECSPI1 (as master) */
&ecspi1 {
fsl,spi-num-chipselects = <1>;
cs-gpios = <&gpio3 26 GPIO_ACTIVE_LOW>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_ecspi1_master>;
status = "okay";
/*
* Add your slave devices here. Next is an example of spidev.
* Expect a harmless kernel warning if you enable spidev as slave.
*/
spidev@0 {
reg = <0>;
compatible = "spidev";
spi-max-frequency = <1000000>;
};
};
&iomuxc {
imx6ul-ccimx6ul {
pinctrl_ecspi1_master: ecspi1grp1 {
fsl,pins = <
MX6UL_PAD_LCD_DATA20__ECSPI1_SCLK 0x10b0
MX6UL_PAD_LCD_DATA22__ECSPI1_MOSI 0x10b0
MX6UL_PAD_LCD_DATA23__ECSPI1_MISO 0x10b0
MX6UL_PAD_LCD_DATA21__GPIO3_IO26 0x10b0 /* Chip Select */
>;
};
};
};SPI user space usage
The SPI bus cannot be accessed directly from user space. Instead, it is accessed via the SPI client drivers. However, a special sample client driver allows raw access to the SPI bus.
SPI device interface
The Linux kernel offers a sample client driver called spidev that gives you read and write data access to the SPI bus through the /dev interface. You can find this driver under the kernel configuration option User mode SPI device driver support (CONFIG_SPI_SPIDEV). On Digi Embedded Yocto this driver is enabled as a loadable module. The default device tree includes the spidev node in the device tree as an SPI device hanging from the SPI bus:
/* ECSPI1 (as master) */
&ecspi1 {
status = "okay";
/*
* Add your slave devices here. Next is an example of spidev.
* Expect a harmless kernel warning if you enable spidev as slave.
*/
spidev@0 {
reg = <0>;
compatible = "spidev";
spi-max-frequency = <1000000>;
};
};To use it, load the spidev module from user space:
~# modprobe spidev spidev spi0.0: buggy DT: spidev listed directly in DT
| Spidev is not a real hardware SPI slave device but a detail of how Linux controls a device. Expect a harmless kernel warning if you enable spidev as slave on the device tree. For reference, see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=956b200a846e324322f6211034c734c65a38e550 |
Linux will create a device node in the form /dev/spidevX.Y device node where:
-
X corresponds to the SPI port index, starting from 0 upwards.
-
Y corresponds to the SPI bus chip select, starting from 0 upwards.
SPI device test application
Build the package dey-examples-spi in your Yocto project to install the test application spidev_test.
This spidev_test application is a simple utility used to test SPI functionality via the spidev device.
Syntax
To display the application’s syntax run:
~# spidev_test --help
Example 1: SPI as master (loopback test)
Short-circuit the MISO and MOSI lines of your SPI bus to create a loopback that allows the bus to receive the same data it is sending.
Run the application using your spidev node /dev/spidevX.Y, where X is the SPI bus index and Y is the SPI bus chip select:
~# spidev_test -D /dev/spidev0.0 -v spi mode: 0x0 bits per word: 8 max speed: 500000 Hz (500 KHz) TX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF F0 0D | ......@....�..................�. RX | FF FF FF FF FF FF 40 00 00 00 00 95 FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF F0 0D | ......@....�..................�.
You should receive the same data displayed in the preceding excerpt.
