Month: August 2020

According to the BCM2711 pin setups[1][2]，Raspberry Pi 4B has 5 exported sets of SPI controllers: SPI3, SPI4, SPI0, SPI5 and SPI1. By default, SCLK of SPI4 and CE1_N of SPI1 share the same GPIO7 pin. When the Linux kernel is fired, a device tree and certain overlays are loaded. We can enable multiple SPI controllers like spi0-cs-overlay.dts in stock firmware[3] does.

We may disable the second chip enable line of SPI0 in first:

/dts-v1/;
/plugin/;
 
 
/ {
        compatible = "brcm,bcm2835";
 
        fragment@0 {
                target = <&amp;spi0_cs_pins>;
                frag0: __overlay__ {
                        brcm,pins = <8>;
                };
        };
 
        fragment@1 {
                target = <&amp;spi0>;
                frag1: __overlay__ {
                        cs-gpios = <&amp;gpio 8 1>;
                        status = "okay";
                };
        };
 
        __overrides__ {
                cs0_pin  = <&amp;frag0>,"brcm,pins:0",
                           <&amp;frag1>,"cs-gpios:4";
        };
};

# compile
dtc -I dts -O dtb -o spi0-1cs.dtbo spi0-1cs.dts
# copy to boot partition
sudo cp spi0-1cs.dtbo /boot/overlays

And then enable SPI3, SPI4, SPI5 and SPI1 which are already given in stock firmware. The following lines should be added into/boot/config.txt. Attention must be paid that we should comment out the default spi=on:

#dtparam=spi=on
dtoverlay=spi0-1cs
dtoverlay=spi3-1cs
dtoverlay=spi4-1cs
dtoverlay=spi1-1cs

We can also apply the previous trick to other device tree overlays. Here I added additional three MCP2515 CAN controllers[4]:

dtoverlay=mcp2515-can0,oscillator=8000000,interrupt=24
dtoverlay=mcp2515-can3,oscillator=8000000,interrupt=25
dtoverlay=mcp2515-can4,oscillator=8000000,interrupt=26
dtoverlay=mcp2515-can1,oscillator=8000000,interrupt=27

Log from dmesg indicated that four CAN controllers were all working smoothly:

pi@raspberrypi:~$ dmesg | grep spi
[    4.387592] spi-bcm2835 fe204600.spi: no tx-dma configuration found - not using dma mode
[    4.391881] spi-bcm2835 fe204600.spi: chipselect 0 already in use
[    4.391898] spi_master spi3: spi_device register error /soc/spi@7e204600/spidev@0
[    4.391915] spi_master spi3: Failed to create SPI device for /soc/spi@7e204600/spidev@0
[    4.392332] spi-bcm2835 fe204800.spi: no tx-dma configuration found - not using dma mode
[    4.394967] spi-bcm2835 fe204800.spi: chipselect 0 already in use
[    4.394982] spi_master spi4: spi_device register error /soc/spi@7e204800/spidev@0
[    4.394999] spi_master spi4: Failed to create SPI device for /soc/spi@7e204800/spidev@0
[    4.419969] spi-bcm2835aux fe215080.spi: chipselect 0 already in use
[    4.419986] spi_master spi1: spi_device register error /soc/spi@7e215080/spidev@0
[    4.420005] spi_master spi1: Failed to create SPI device for /soc/spi@7e215080/spidev@0
[    5.351820] mcp251x spi0.0 can0: MCP2515 successfully initialized.
[    5.368085] mcp251x spi3.0 can1: MCP2515 successfully initialized.
[    5.379651] mcp251x spi4.0 can2: MCP2515 successfully initialized.
[    5.390782] mcp251x spi1.0 can3: MCP2515 successfully initialized.

[1] https://elinux.org/RPi_BCM2711_GPIOs
[2] https://www.raspberrypi.org/documentation/usage/gpio/
[3] https://github.com/raspberrypi/linux/blob/rpi-5.4.y/arch/arm/boot/dts/overlays/spi0-cs-overlay.dts
[4] https://github.com/raspberrypi/linux/blob/rpi-5.4.y/arch/arm/boot/dts/overlays/mcp2515-can0-overlay.dts