SPI (Linux)
Introduction
The Apalis standard provides two SPI interfaces compatible with all modules of the Apalis family.
| MXM3 Pin | Apalis Signal Name | Description |
|---|---|---|
| 225 | SPI1_MOSI | SPI Master Output, Slave Input; SPI Data Out (DOUT) |
| 223 | SPI1_MISO | SPI Master Input, Slave Output; SPI DATA In (DIN) |
| 227 | SPI1_CS | SPI Chip Select; SPI Enable Signal; SPI Slave Select |
| 221 | SPI1_CLK | SPI Serial Clock; (SCK) |
| 231 | SPI2_MOSI | SPI Master Output, Slave Input; SPI Data Out (DOUT) |
| 229 | SPI2_MISO | SPI Master Input, Slave Output; SPI DATA In (DIN) |
| 233 | SPI2_CS | SPI Chip Select; SPI Enable Signal; SPI Slave Select |
| 235 | SPI2_CLK | SPI Serial Clock; (SCK) |
The Colibri standard provides one SPI interface compatible with all modules of the Colibri family which historically is called Synchronous Serial Port (SSP).
| SODIMM Pin | Colibri Signal Name | SSP Description | SPI Description |
|---|---|---|---|
| 86 | SSPFRM | Synchronous Serial Port Frame | SPI Chip Select; SPI Enable Signal; SPI Slave Select |
| 88 | SSPSCLK | Synchronous Serial Port Clock | SPI Serial Clock; (SCK) |
| 90 | SSPRXD | Synchronous Serial Port Receive | SPI Master Input / Slave Output (MISO); SPI DATA In (DIN) |
| 92 | SSPTXD | Synchronous Serial Port Transmit | SPI Master Output / Slave Input (MOSI); SPI Data Out (DOUT) |
The Verdin Family Specification provides one SPI interface in the category Always Compatible, available on all modules of the Verdin family. The interface features a single chip select pin.
| SODIMM Pin | Apalis Signal Name | Description |
|---|---|---|
| 196 | SPI_1_CLK | SPI Serial Clock; (SCK) |
| 198 | SPI_1_MISO | SPI Master Input, Slave Output; SPI DATA In (DIN) |
| 200 | SPI_1_MOSI | SPI Master Output, Slave Input; SPI Data Out (DOUT) |
| 202 | SPI_1_CS | SPI Chip Select; SPI Enable Signal; SPI Slave Select |
The standard SPI interfaces are enabled by default. Most modules offer additional (non-standard) SPI interfaces, to enable these device trees or board files aka platform data customization is required.
The Colibri Evaluation Board provides an MCP2515 SPI CAN controller. For Colibri modules the kernel driver for this CAN controller is active by default and no userspace SPI access is possible, i.e. the /dev/spidevA.B device files are not available. See the carrier board section for further information.
Modules
Apalis
The Apalis module standard features two generic SPI interface:
| SoM Interface | Device nodes names | Note |
|---|---|---|
| SPI1 | /dev/apalis-spi1-cs0 | General Purpose |
| SPI2 | /dev/apalis-spi2-cs0 | General Purpose |
To obtain the device nodes names for the Apalis module family:
# ls -l /dev/apalis-spi*
It will display the available Apalis pin-compatible SPIs and display the corresponding names used by the BSP. Those corresponding names are important because the Linux kernel logs will print the real device names (e.g. /dev/spidev3.0), not the Apalis symlinks (e.g. /dev/apalis-spi1-cs0).
For non-standard interfaces, consult the specific SoM datasheet.
Colibri
The Colibri module standard features only one generic SPI interface:
| SoM Interface | Device nodes names | Note |
|---|---|---|
| SPI1 | /dev/colibri-spi-cs0 | General Purpose |
To obtain the device nodes names for the Colibri module family:
# ls -l /dev/colibri-spi*
It will display the available Colibri pin-compatible SPIs and display the corresponding names used by the BSP. Those corresponding names are important because the Linux kernel logs will print the real device names (e.g. /dev/spidev3.0), not the Colibri symlinks (e.g. /dev/colibri-spi-cs0).
For non-standard interfaces, consult the specific SoM datasheet.
Verdin
The Verdin module standard features only one generic SPI interface:
| SoM Interface | Device nodes names | Note |
|---|---|---|
| SPI1 | /dev/verdin-spi-cs0 | General Purpose |
To obtain the device nodes names for the Verdin module family:
# ls -l /dev/verdin-spi*
It will display the available Verdin pin-compatible SPIs and display the corresponding names used by the BSP. Those corresponding names are important because the Linux kernel logs will print the real device names (e.g. /dev/spidev3.0), not the Verdin symlinks (e.g. /dev/verdin-spi-cs0).
For non-standard interfaces, consult the specific SoM datasheet.
Verdin iMX8M Mini modules do not have a native CAN Controller. So, for using CAN, it requires the usage of an external CAN Controller through SPI port. You can read more about this at CAN (Linux)
Carrier Boards
Colibri Evaluation board
By default our BSPs use the MCP2515 SPI CAN controller as available on our Colibri Evaluation board V3.x.
For eMMC-based SoMs, there is an overlay, colibri-imx6-eval_spidev_overlay.dtbo, so in order to use it, you should add it on the overlays.txt file in the /boot directory. To do this, open the file with the following command and add this overlay binary to the fdt_overlays= variable.
# vi /boot/overlays.txt
In this case, here is how it was before:
fdt_overlays=colibri-imx6_lcd-vga_overlay.dtbo colibri-imx6_stmpe-ts_overlay.dtbo
And here is how it should be after:
fdt_overlays=colibri-imx6_lcd-vga_overlay.dtbo colibri-imx6_stmpe-ts_overlay.dtbo colibri-imx6-eval_spidev_overlay.dtbo
For NAND-based SoMs, in order to use spidev instead one needs to disable (e.g. status = "disabled") the mcp2515 device tree node and enable (e.g. status = "okay") the spidev one and re-generate and deploy the device tree to the target. The specific changes are outlined below, as an example, the device tree for a Colibri iMX7 is given:
diff --git a/arch/arm/boot/dts/imx7-colibri-eval-v3.dtsi b/arch/arm/boot/dts/imx7-colibri-eval-v3.dtsi
index 1db5aa5..28a8bc7 100644
--- a/arch/arm/boot/dts/imx7-colibri-eval-v3.dtsi
+++ b/arch/arm/boot/dts/imx7-colibri-eval-v3.dtsi
@@ -101,14 +101,14 @@
interrupt-parent = <&gpio5>;
interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
spi-max-frequency = <10000000>;
- status = "okay";
+ status = "disabled";
};
spidev0: spidev@0 {
compatible = "toradex,evalspi";
reg = <0>;
spi-max-frequency = <23000000>;
- status = "disabled";
+ status = "okay";
};
};
Aster Carrier Board
Aster doesn't include the mcp2515 SPI CAN controller, so spidev is enabled by default. As SPI is accessible on both X18 and X20 two chip selects are configured, one for the X18 connector and the other one for the X20 connector. Thus two spidev devices appear, for a Colibri iMX7 e.g. spidev2.0 CS signal is available on X18 ONLY, and spidev2.1 CS signal is available on X20 ONLY. Refer to the following table:
| SODIMM Pin | Colibri Signal Name | Signal | X18 pin | X20 pin |
|---|---|---|---|---|
| 86 | SSPFRM | CS0 | 3 | |
| 65 | CIF_D9 | CS1 | 24 | |
| 88 | SSPSCLK | CLK | 6 | 23 |
| 90 | SSPRXD | MISO | 5 | 21 |
| 92 | SSPTXD | MOSI | 4 | 19 |
User-space access
SPI access from user-space is provided through the spidev driver which exports device files under /dev. See Documentation/spi/spidev in the kernel sources for more information.
The following shows a read using the sample code in the kernel sources (Documentation/spi/spidev_test.c) using spidev interface:
# spidev_test -D /dev/spidev3.0
spi mode: 0x0
bits per word: 8
max speed: 500000 Hz (500 KHz)
Kernel-space drivers
The Linux kernel already provides drivers for various SPI devices, hence before writing your own driver checking your Linux kernels configuration options and/or searching through the kernel mailing list is best practice.
If you plan to write an SPI device driver you can use the SPI MCP2515 CAN controller driver as an example. The MCP2515 CAN controller is available and connected to the Colibri SPI port on the v3 series of the Colibri Evaluation Board.