Driver development for Raspberry Pi

Aug 6 2019 Linux驱动开发 5 minutes read (About 747 words)

The hardware driver development is involved in the operating system programming.

Prerequisites

Before we start the driver development, the Linux kernel has to be manually built at least once. So the next two ways will be introduced for building Pi linux kernel, one way is to self compile on Raspberry Pi, another is to compile it on a host Linux computer and then copyed to RPi. First of all, download the linux kernel package Raspberry github’s page: https://github.com/raspberrypi/linux/releases with the same version as your Raspbian Linux version. You can check your Raspbian linux version by

My current raspbian linux kernel version is v4.19.57(2019-07-25), so I download 4.19.y linux.

Cross compile on Arch Linux

Download or git clone and ‘tools’ repository from

1	git clone --depth=1 https://github.com/raspberrypi/tools ./tools

For Arch Linux, some basic packages for cross-compiling are required and can be installed by sudo pacman -Syu bison flex openssl p7zip. Use 7z x rather than unzip to extract linux kernel file(unzip somewhat doesn’t support very long full path). Then manually copy the config file from the running pi to the source code tree and configure it further:

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cd linux
KERNEL=kernel7
make bcm2709_defconfig

Error: Can’t find default configuration “arch/x86/configs/bcm2709_defconfig”!
It’s reseasonable because this config file hasn’t been created. So 1st method is to generate one:

1	make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- bcm2709_defconfig

2nd alternative method is to copy one from rpi. On RPi:

1 2	sudo modprobe configs sudo cp /proc/config.gz ~/Documents

Back Arch

scp -P2022 pi@raspberry:~/Documents/config.gz [directory/of/linux]
zcat config.gz > .config

make ARCH=arm CROSS_COMPILE=../tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf- zImage -j4
make ARCH=arm CROSS_COMPILE=../tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf- modules -j8
make ARCH=arm CROSS_COMPILE=../tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf- dtbs -j4

Type enter for default settings when encounting input waiting.

Insert RPi TF card and check it via lsblk, then mount

sudo mkdir /mnt/fat32
sudo mkdir /mnt/ext4
sudo mount /dev/sdb6 mnt/fat32
sudo mount /dev/sdb7 /mnt/ext4
sudo make ARCH=arm CROSS_COMPILE=../tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf- INSTALL_MOD_PATH=/mnt/ext4 modules_install
KERNEL=kernel7
ls /mnt/fat32 -l | grep img
sudo cp arch/arm/boot/zImage /mnt/fat32/kernel-myconfig.img
sudo cp arch/arm/boot/dts/*.dtb /mnt/fat32/  
sudo cp arch/arm/boot/dts/overlays/*.dtb* /mnt/fat32/overlays 
sudo cp arch/arm/boot/dts/overlays/README /mnt/fat32/overlays

sudo edit /mnt/fat32/config.txt file:

1	kernel=kernel-myconfig.img

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sudo umount /mnt/fat32
sudo umount /mnt/ext4
lsblk

Re-insert TF card into Pi and start, type uname -r to check. It’s 4.19.64+. Succeed~

Self compile on RPi4

ssh into pi and scp those two folders.

extract and enter ‘linux-rpi-x.xx.x’ and type

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sudo apt install bc bison flex libssl-dev
KERNEL=kernel7l
make bcm2711_defconfig

make -j4 zImage modules dtbs
sudo make modules_install
sudo cp arch/arm/boot/dts/*.dtb /boot/
sudo cp arch/arm/boot/dts/overlays/*.dtb* /boot/overlays/
sudo cp arch/arm/boot/dts/overlays/README /boot/overlays/
sudo cp arch/arm/boot/zImage /boot/$KERNEL.img

Check the new kernel version:

LED driver Experiment

Makefile

ifneq ($(KERNELRELEASE),)
        obj-m :=hello.o
else
    KERNELDIR :=/home/shane/Downloads/Raspberry-Pi/linux/
all:
        $(MAKE) -C $(KERNELDIR) M=$(PWD) ARCH=arm CROSS_COMPILE=/home/shane/Downloads/Raspberry-Pi/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf- modules
clean:
        rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modul*
endif

make and then scp hello.ko file. On RPi

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sudo insmod hello.ko
sudo rmmod hello
dmesg | tail -5

[ 7804.521916] smsc95xx 1-1.1:1.0 enxb827eb802252: link down
[ 7839.258242] smsc95xx 1-1.1:1.0 enxb827eb802252: link up, 100Mbps, full-duplex, lpa 0xCDE1
[ 8655.103844] hello: loading out-of-tree module taints kernel.
[ 8655.110062] Hello, world
[ 8726.505905] Goodbye, world

Procedures conclusion

Write a driver file
Compile, build and sudo insmod some-name.ko
Write the test test
Compile, build and sudo ./test

References

https://www.raspberrypi.org/documentation/linux/kernel/building.md

#Raspberry Pi #Linux kernel