Supporting SPI in the Linux i.MX RT10XX BSP

Owned by Natalia Sofronova
Last updated: yesterday at 2:34 am
7 min read

 

This is an add-on product that installs on top of the Linux BSP for the NXP i.MX RT10XX EVK board. It must be purchased separately from the Linux BSP product.

1. Overview

This document describes how to support for the LPSPI controller of the i.MX RT10XX processor in the Linux BSP.

2. Requirements

2.1. Detailed Requirements

The following are the requirements for this project:

  1. Provide a Linux demo project combining all the requirements in this project.

  2. Provide support for the i.MX RT1050 LPSPI controller in Linux.

  3. Provide support for the raw access to the SPI device from user space.

2.2. Detailed Non-Requirements

The following are the non-requirements for this project that may otherwise not be obvious:

  • None

3. Design

3.1. Detailed Design

3.1.1. Design: Demo Project

This project will enable the required functionality in the Linux configuration ("embedded project") called rootfs, which resides in a projects/rootfs directory, relative to the top of the Linux i.MX RT1050 or i.MX RT1060 installation.

3.1.2. Design: Linux LPSPI Device Driver

In the i.MXRT1050/1060 SoC, the LPSPI controller is compatible with the same controller of some other SoCs from the i.MX family, so the existing spi-fsl-lpspi.c driver in the Linux sources, which was initially added to support SPI in the i.MX7ULP SoC, will be used to support the LPSPI controller of the i.MXRT1050/1060 SoC.

To enable the driver, the standard CONFIG_SPI along with the CONFIG_SPI_FSL_LPSPI options will be defined in the kernel defconfig file.

In addition to the kernel defconfig, the user must configure the LPSPI controller in DTS. Refer to https://www.kernel.org/doc/Documentation/devicetree/bindings/spi/spi-controller.yaml for details on format of the SPI nodes.

The DTS nodes for all 4 instances of the i.MXRT1050/1060 LPSPI controller will be predefined in arch/arm/boot/dts/nxp/imx/imxrt1050.dtsior in arch/arm/boot/dts/nxp/imx/imxrt1060.dtsi. The clock driver for the i.MXRT1050/1060 SoC will be updated to support the LPSPI clocks. Interrupts and clocks will be defined in the DTS nodes according to the processor reference manual. All controllers will be configured to use the DMA. All the SPI nodes in the .dtsi file will be disabled by default.

Final tuning of the kernel run-time configuration, such as defining the pinctrl settings for a custom connection of an SPI device to the LPSPI controller, defining the chip-select signal, customizing the clocks etc, will be done in the user DTS file.

This project will provide an example for configuring the LPSPI1 controller. There are no SPI devices on the IMXRT1050/1060-EVKB board connected to the LPSPI controller, so external SPI Flash connected via the SD TF to TF Flexible Card Extension cable will be used to demonstrate reading the SPI device registers.

The lpspi1 node will be configured in the rootfs.dts.IMXRT105X_NXPEVK or in the rootfs.dts.IMXRT106X_NXPEVK file as follows:

&lpspi1 { pinctrl-names = "default"; pinctrl-0 = <&pinctrl_lpspi1>; status = "okay"; cs-gpios = <&gpio3 13 GPIO_ACTIVE_LOW>; num-chipselects = <1>; ... }; &iomuxc { ... pinctrl_lpspi1: lpspi1grp { fsl,pins = < MXRT1050_IOMUXC_GPIO_SD_B0_00_LPSPI1_SCK MXRT10XX_PAD_CFG_SPI MXRT1050_IOMUXC_GPIO_SD_B0_02_LPSPI1_SDO MXRT10XX_PAD_CFG_SPI MXRT1050_IOMUXC_GPIO_SD_B0_03_LPSPI1_SDI MXRT10XX_PAD_CFG_SPI /* CS#1 (SPI Flash) */ MXRT1050_IOMUXC_GPIO_SD_B0_01_GPIO3_IO13 MXRT10XX_PAD_CFG_GPIO >; }; };

This example assigns the i.MXRT1050/1060 pinctrl PADs GPIO_SD_B0_00, GPIO_SD_B0_01, GPIO_SD_B0_02 and GPIO_SD_B0_03 to the LPSPI1 controller and selects the LPSPI1_SCK, GPIO, LPSPI1_SDO and LPSPI1_SDI functions for these PADs (refer to the board schematics and to the processor reference manual for details on possible IOMUXC configurations).

The single chip-select is configured to the GPIO3 13 signal in the example.

Due to the fact that the GPIO_SD_B0_00, GPIO_SD_B0_01, GPIO_SD_B0_02 and GPIO_SD_B0_03 PADs are used for the SD card controller, the changes for LPSPI1 will be provided under the #if defined(SPI_FLASH_ON_LPSPI1) condition. If the SPI_FLASH_ON_LPSPI1 is defined in DTS, the SD-card controller will be disabled.

3.1.3. Design: Raw SPI Device Access

Linux provides a special spidev device driver to allow raw accesses to SPI devices from the user space: https://www.kernel.org/doc/Documentation/spi/spidev.

The standard Linux CONFIG_SPI_SPIDEV option will be defined in the kernel defconfig file to enable the spidev driver. The universal compatibility string "linux,spidev" will be added to the spidev driver so that it can be used in the project DTS.

The following changes will be made to rootfs.dts.IMXRT105X_NXPEVK to link an external SPI Flash to the spidev Linux device:

&lpspi1 { ... #if defined(LPSPI_USE_SPIDEV) spidev: spidev@0 { status = "okay"; compatible = "linux,spidev"; spi-max-frequency = <33000000>; reg = <0>; }; ... #endif };

The following test program spidev_flash will be included to the project root file system as an example on how to read the Flash ID of an SPI Flash device from the user-space applications:

/* * Sample application that makes use of the SPIDEV interface * to access an SPI slave device. Specifically, this sample * reads a Device ID of a JEDEC-compliant SPI Flash device. */ #include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <unistd.h> #include <sys/ioctl.h> #include <linux/types.h> #include <linux/spi/spidev.h> #include <stdint.h> #include <stdio.h> #include <string.h> #include <errno.h> int main(int argc, char **argv) { char *name; int fd; struct spi_ioc_transfer xfer[2]; unsigned char buf[32], *bp; int len, status; name = argv[1]; fd = open(name, O_RDWR); if (fd < 0) { perror("open"); return 1; } memset(xfer, 0, sizeof xfer); memset(buf, 0, sizeof buf); len = sizeof buf; /* * Send a GetID command */ buf[0] = 0x9f; len = 6; xfer[0].tx_buf = (unsigned long)buf; xfer[0].len = 1; xfer[1].rx_buf = (unsigned long) buf; xfer[1].len = 6; status = ioctl(fd, SPI_IOC_MESSAGE(2), xfer); if (status < 0) { perror("SPI_IOC_MESSAGE"); return -1; } printf("response(%d): ", status); for (bp = buf; len; len--) printf("%02x ", *bp++); printf("\n"); return 0; }

3.2. Effect on Related Products

This project makes the following updates in the related products:

  • None

3.3. Changes to User Documentation

This project updates the following user documents:

  • None

3.4. Alternative Design

The following alternative design approaches were considered by this project but then discarded for some reason:

  • None

4. Test Plan

4.1. Secure Download Area

The downloadable materials developed by this project are available from a secure Web page on the Emcraft Systems web site. Specifically, proceed to the following URL to download the software materials:

  • For the i.MX RT1050 BSP (release 3.0.4):

https://www.emcraft.com/imxrtaddon/imxrt1050/lpspi/

The page is protected as follows:

Login: CONTACT EMCRAFT

Password: CONTACT EMCRAFT

  • For the i.MX RT1050 BSP (release 3.1.0):

https://www.emcraft.com/imxrtaddon/imxrt1050-3.1.0/lpspi/

The page is protected as follows:

Login: CONTACT EMCRAFT

Password: CONTACT EMCRAFT

  • For the i.MX RT1060 BSP (release 3.1.0):

https://www.emcraft.com/imxrtaddon/imxrt1060-3.1.0/lpspi/

The page is protected as follows:

Login: CONTACT EMCRAFT

Password: CONTACT EMCRAFT

4.2. Downloadable Files

The following files are available from the secure download area:

  • linux-lpspi.patch - patch to the Linux kernel sources;

  • projects-lpspi.patch - patch to the rootfs project;

  • rootfs.uImage - prebuilt bootable Linux image;

4.3. Test Set-Up

4.3.1. Hardware Setup

The following hardware setup is required for the i.MX RT 1050/1060 board:

  • The i.MXRT1050 EVKB board or i.MXRT1060 EVKB board.

  • Micron M25P32 SPI Flash Memory, as a separate chip.

  • Connect the SPI Flash memory via the "SD TF to TF Flexible Card Extension cable Extender Adapter" attached to the TF Card Slot J20. Details of those connection are as follows:

SPI Memory Signal/Function

J20 Pin#

MCU Signal

MCU PAD

CS#/Chip Select

5

LPSPI1_PCS0

GPIO_SD_B0_01

SCLK/Clock Input

3

LPSPI1_SCK

GPIO_SD_B0_00

SI/Serial Data Input

7

LPSPI1_SDO

GPIO_SD_B0_02

SO/Serial Data Output

8

LPSPI1_SDI

GPIO_SD_B0_03

4.3.2. Software Setup

The following software setup is required:

  1. Download the files listed in Section: "Downloadable Files" to the top of the Linux i.MX RT installation.

  2. Install the BSP, as per the respective "Installing and activating cross development environment" document in the "Software" section on the Emcraft site.

  3. From the top of the Linux installation, activate the Linux cross-compile environment by running:

  4. From the top of the BSP installation, go to the Linux kernel tree and install the kernel patch, eg:

  5. From the top of the Linux installation, go to the projects sub-directory, and patch the rootfs project:

  6. Build the rootfs project:

4.4. Detailed Test Plan

4.4.1. Test Plan: Demo Project

Perform the following step-wise test procedure:

  1. Go to the projects/rootfs directory, build the loadable Linux image (rootfs.uImage) and copy it to the TFTP directory on the host:

  2. Boot the loadable Linux image (rootfs.uImage) to the target via TFTP and validate that it boots to the Linux shell:

4.4.2. Test Plan: Linux LPSPI Driver

Perform the following step-wise test procedure:

  1. From the Linux shell, run dmesg and verify that there are no error messages related to SPI or LPSPI:

  2. Verify that the spi0 master is registered in the sysfs:

4.4.3. Test Plan: Raw SPI Device Access

  1. Replace the SD card in the SD card slot by the SPI Flash memory M25P32 using "SD TF to TF Flexible Card Extension cable Extender Adapter".

  2. Make sure the spidev device exists:

  3. Make sure the spidev_flash application reads the correct Flash ID over SPI (first 3 bytes must be 0x20 0x20 0x16 for the M25P32 Flash connected the IMXRT1050-EVK board):