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Enable SPI interface on Jetson-Nano

Introduction​

The Jetson Nano features two SPI interfaces multiplexed with GPIOs, but SPI is not enabled by default. Unlike other Jetson series such as Orin, which support enabling SPI via the configuration tool /opt/nvidia/jetson-io/jetson-io.py, this method is not applicable on the Jetson Nano.

This section uses the SPI1 controller as an example and provides a method for enabling SPI functionality on the Jetson Nano. Note that this method must be applied before flashing the image to the Jetson device.

note

The method of this wiki must be applied before flashing the image to the Jetson device.

Modify spi and flashing​

First, you need to short the REC pin and GND pin on the Jetson Nano to enter recovery mode. Then, on your host PC, prepare the image you intend to flash. However, do not flash it to the Jetson Nano until you have completed the SPI modifications. You can refer to the flashing JetPack tutorial for the J101, and make sure to use the Command Line method only.

Download the version of your choice from the NIVIDIA DEVELOPER, including the BSP and the Simple Root Filesystem. In this guide, we use L4T 32.7.2 as an example.

Place the BSP and the Simple Root Filesystem in the same directory, then follow the instructions below to extract them and run the apply_binaries.sh:

tar xf Jetson-210_Linux_R32.7.2_aarch64.tbz2
cd Linux_for_Tegra/rootfs/
sudo tar xpf ../../Tegra_Linux_Sample-Root-Filesystem_R32.7.2_aarch64.tbz2
cd ..
sudo ./apply_binaries.sh

Create a new .sh file in the Linux_for_Tegra directory, and run the script. The script content is as follows:

modify_spi.sh 
#!/bin/bash
set -e


cd "$(dirname "$0")"
cd kernel/dtb

DTS=tegra210-p3448-0002-p3449-0000-b00.dts
DTB=tegra210-p3448-0002-p3449-0000-b00.dtb


echo "📥 Decompiling $DTB to $DTS..."
sudo dtc -I dtb -O dts -o "$DTS" "$DTB"

fix_spi_node() {
    local node=$1
    if grep -A5 "$node {" "$DTS" | grep -q 'status'; then
        sudo sed -i "/$node {/,/spi-max-frequency/ s/status = \".*\";/status = \"okay\";/" "$DTS"
    else
        sudo sed -i "/$node {/,/spi-max-frequency/ s/compatible = \"tegra-spidev\";/&\n\t\tstatus = \"okay\";/" "$DTS"
    fi
}

echo "🔧 Enabling spi@0 and spi@1..."
fix_spi_node "spi@0"
fix_spi_node "spi@1"


patch_pin() {
    local pin=$1
    sudo sed -i "/${pin} {/,/nvidia,enable-input/ {
        s/nvidia,function = \"rsvd1\"/nvidia,function = \"spi1\"/
        s/nvidia,tristate = <0x01>/nvidia,tristate = <0x00>/
        s/nvidia,enable-input = <0x00>/nvidia,enable-input = <0x01>/
    }" "$DTS"
}

echo "🔧 Patching pinmux blocks..."
for pin in spi1_mosi_pc0 spi1_miso_pc1 spi1_sck_pc2 spi1_cs0_pc3 spi1_cs1_pc4; do
    patch_pin "$pin"
done

echo "🔧 Fixing tristate and input-enable for SPI1 pins..."


fix_pinmux_field() {
  local pin=$1
  awk -v pin="$pin" '
  BEGIN { in_block = 0 }
  {
    if ($0 ~ pin " {") {
      in_block = 1
    }
    if (in_block && /nvidia,tristate =/) {
      sub(/<0x1>/, "<0x0>")
    }
    if (in_block && /nvidia,enable-input =/) {
      sub(/<0x0>/, "<0x1>")
    }
    print
    if (in_block && /}/) {
      in_block = 0
    }
  }' "$DTS" | sudo tee "$DTS.fixed" > /dev/null && sudo mv "$DTS.fixed" "$DTS"
}

fix_pinmux_field "spi1_mosi_pc0"
fix_pinmux_field "spi1_miso_pc1"
fix_pinmux_field "spi1_sck_pc2"
fix_pinmux_field "spi1_cs0_pc3"
fix_pinmux_field "spi1_cs1_pc4"


echo "📦 Recompiling DTS to $DTB..."
sudo dtc -I dts -O dtb -o "$DTB" "$DTS"

echo "✅ SPI DTS patch applied and DTB regenerated successfully."
sudo bash modify_spi.sh

After running modify_spi.sh. This script will update the SPI1 configuration in the device tree, recompile it, and overwrite the old one. If you want to enable SPI2, simply replace the keyword spi1 with spi2 in the modify_spi.sh script.

After modifying the device tree, flash the image to the Jetson-Nano: 

sudo ./flash.sh jetson-nano-emmc mmcblk0p1

After rebooting, the SPI0_MOSI, SPI0_MISO, SPI0_CS0, and SPI0_CS1 pins on the 40-pin header will be available for use.

Testing the SPI1 on Jetson-nao​

Short pin 19 and pin 21, which correspond to SPI0_MOSI and SPI0_MISO respectively, to perform a loopback test using the SPI1 controller. The Jetson-Nano datasheet can be downloaded and viewed here, particularly page 6.

The physical connection diagram is shown below:

Load the SPI driver module, then download and compile the test program: 

sudo modprobe spidev
git clone https://github.com/rm-hull/spidev-test
cd spidev-test/
gcc spidev_test.c -o spidev_test

Run the test program and specify spidev0.0 (corresponding to SPI1):

./spidev_test -v -D /dev/spidev0.0 -p "Test"

The test result is shown below, indicating that SPI1 has successfully completed the loopback transmission. You can also run ls /dev/spidev* to check the available SPI controllers.

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