After GIT clone this repository, please update submodule.
git submodule init
git submodule update
To avoid source code mixed with buildroot or linux kernel, the custome-app directory contains the linux module/driver source codes. The br2-external mechanism is adopted, the outside of the Buildroot tree is external directory, as follows.
external/
├── board
│ ├── labs
│ │ ├── genimage.cfg
│ │ ├── linux-4.1-sgx.fragment
│ │ ├── linux.config
│ │ ├── post-image.sh
│ │ ├── readme.txt
│ │ ├── rootfs-overlay
│ │ │ └── etc
│ │ │ └── network
│ │ │ └── interfaces
│ │ ├── uEnv-nfs.txt
│ │ ├── uEnv-sd.txt
│ │ └── uEnv.txt
│ └── qemu
│ └── linux.config
├── Config.in
├── configs
│ ├── labs_defconfig
│ └── qemu_defconfig
├── external.desc
├── external.mk
└── package
├── ldd-misc-modules
│ ├── Config.in
│ └── ldd-misc-modules.mk
├── ldd-scull
│ ├── Config.in
│ └── ldd-scull.mk
├── led
│ ├── Config.in
│ └── led.mk
└── sample-app
├── Config.in
└── sample-app.mk
I adopt Buildroot 2018.05 verion.
cd buildroot
git checkout -b v2018.05 2018.05
Make build for beaglebone black as follows.
make BR2_EXTERNAL=$PWD/external -C $PWD/buildroot O=$PWD/output-bbb labs_defconfig
cd $PWD/output-bbb
make -C ../buildroot O=$(pwd) menuconfig
make menuconfig
make
make savedefconfig # Save current config to BR2_DEFCONFIG (minimal config)
If you want to config linux, the following commands are helpful.
make linux-menuconfig # Run Linux kernel menuconfig
make linux-savedefconfig # Run Linux kernel savedefconfig
make linux-update-defconfig # Save the Linux configuration to the path specified
Make build for qemu as follows.
make BR2_EXTERNAL=$PWD/external -C $PWD/buildroot O=$PWD/output-qemu qemu_defconfig
make -C $PWD/output-qemu
As the results, you will get two directories: output-bbb, output-qemu.
I get a USB to TTL Serial Debug Cable for Raspberry Pi from https://www.adafruit.com/product/954.
Install minicom (Linux) or putty (Windows) on the Host computer. Set the serial port (usb to serial board) to 115200 baud, 8 data bits, no parity, 1 stop bit, no flow control.
Make the bootable SD card.
sudo dd if=/dev/zero of=/dev/sdc bs=1M count=16
sudo cfdisk /dev/sdc
sudo mkfs.vfat -F 16 -n boot /dev/sdc1
sudo mkfs.ext4 -L rootfs -E nodiscard /dev/sdc2
NOTE: /dev/sdc maybe different in your machine's configuration.
My SD card is mounted in /media/bill/boot, I can flash as follows.
cd output-bbb/images
cp MLO u-boot.img zImage am335x-boneblack.dtb uEnv.txt /media/bill/boot/
sudo tar -C /media/bill/rootfs -xf rootfs.tar
Then the SD card can be used for boot, using following uEnv.txt:
bootpart=0:1
devtype=mmc
bootdir=
bootfile=zImage
bootpartition=mmcblk0p2
set_mmc1=if test $board_name = A33515BB; then setenv bootpartition mmcblk1p2; fi
set_bootargs=setenv bootargs console=ttyO0,115200n8 root=/dev/${bootpartition} rw rootfstype=ext4 rootwait
uenvcmd=run set_mmc1; run set_bootargs;run loadimage;run loadfdt;printenv bootargs;bootz ${loadaddr} - ${fdtaddr}
After setup TFTP server(/tftproot/)and NFS server(/rootfs), execute the following:
cd output-bbb/images
cp MLO u-boot.img zImage am335x-boneblack.dtb uEnv.txt /tftproot/
sudo tar -C /rootfs -xf rootfs.tar
We can boot from tftp server and NFS server, using following uEnv.txt
fdtfile=am335x-boneblack.dtb
fdtaddr=0x88000000
bootfile=zImage
loadaddr=0x82000000
console=ttyO0,115200n8
serverip=192.168.0.104
ipaddr=192.168.0.105
rootpath=/rootfs
netloadfdt=tftp ${fdtaddr} ${fdtfile}
netloadimage=tftp ${loadaddr} ${bootfile}
netargs=setenv bootargs console=${console} ${optargs} root=/dev/nfs nfsroot=${serverip}:${rootpath},nolock,nfsvers=3 rw rootwait ip=${ipaddr}
netboot=echo Booting from network ...; setenv autoload no; run netloadimage; run netloadfdt; run netargs; bootz ${loadaddr} - ${fdtaddr}
uenvcmd=run netboot
If you want to add some executables in the build, just follow my sample-app example.
I will use the example in the book: Linux Device Drivers, Third Edition (https://lwn.net/Kernel/LDD3/).
make ldd-misc-modules-rebuild
make
make update-servers
NOTE: I add the customized "make update-servers" to update the tftp and nfs server with the latest build. Please refer to external.mk for details.
Now you can reboot your Beaglebone black to verify if it works.
This example need breadboard to setup some circuit connect beaglebone's GPIO, button, and LED. For details, please refer to http://derekmolloy.ie/kernel-gpio-programming-buttons-and-leds. It introduces kobjects and a mechanism for adding your own entries to Sysfs. This allows you to send data to and receive data from the LKM at run time.
We can use breadboard to connect GPIO with Button LED. I have adapted the source codes a little to work in current linux version.
make led-rebuild
make
make update-servers
To run in Qemu, execute:
cd output-qemu
qemu-system-arm -M vexpress-a9 -smp 1 -m 256 -display none \
-kernel "$OUTPUT_PATH"/images/zImage \
-dtb "$OUTPUT_PATH"/images/vexpress-v2p-ca9.dtb \
-drive file="$OUTPUT_PATH"/images/rootfs.ext2,if=sd,format=raw \
-append "console=ttyAMA0,115200 root=/dev/mmcblk0" \
-serial mon:stdio \
-net nic,model=lan9118 -net user
-s -S
~/bbb/output-qemu/build/linux-4.14$ arm-linux-gnueabihf-gdb vmlinux
GNU gdb (Linaro_GDB-2017.11) 8.0.1.20171119-git
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64-unknown-linux-gnu --target=arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from vmlinux...done.
(gdb) c
The program is not being run.
(gdb) target remote :1234
Remote debugging using :1234
0x60000000 in ?? ()
(gdb) c
Continuing.
Welcome to Buildroot
buildroot login: root
Password:
#
#
# cd /lib/modules/4.14.0/extra/
# ls
complete.ko hellop.ko scull.ko seq.ko
faulty.ko kdataalign.ko scull_load silly.ko
hello.ko kdatasize.ko scull_unload sleepy.ko
# ./scull_load
scull: loading out-of-tree module taints kernel.
scullsingle registered at fb00008
sculluid registered at fb00009
scullwuid registered at fb0000a
scullpriv registered at fb0000b
# ls -a /sys/module/scull/sections/
. .rodata
.. .rodata.str1.4
.ARM.exidx .strtab
.alt.smp.init .symtab
.bss .text
.data .text.fixup
.gnu.linkonce.this_module __ex_table
.note.gnu.build-id __param
# cat /sys/module/scull/sections/.text
0x7f000000
^C
Program received signal SIGINT, Interrupt.
cpu_v7_do_idle () at arch/arm/mm/proc-v7.S:80
80 ret lr
(gdb) add-symbol-file /home/bill/bbb/output-qemu/build/ldd-scull/scull.ko 0x7f000000
add symbol table from file "/home/bill/bbb/output-qemu/build/ldd-scull/scull.ko" at
.text_addr = 0x7f000000
(y or n) y
Reading symbols from /home/bill/bbb/output-qemu/build/ldd-scull/scull.ko...done.
(gdb) l scull_read
290 * Data management: read and write
291 */
292
293 ssize_t scull_read(struct file *filp, char __user *buf, size_t count,
294 loff_t *f_pos)
295 {
296 struct scull_dev *dev = filp->private_data;
297 struct scull_qset *dptr; /* the first listitem */
298 int quantum = dev->quantum, qset = dev->qset;
299 int itemsize = quantum * qset; /* how many bytes in the listitem */
(gdb) b main.c:296
# echo "11111" > /dev/scull0
# cat /dev/scull0
┌──/home/bill/bbb/output-qemu/build/ldd-scull/./main.c────────────────────────────────────────────────────┐
│282 } │
│283 qs = qs->next; │
│284 continue; │
│285 } │
│286 return qs; │
│287 } │
│288 │
│289 /* │
│290 * Data management: read and write │
│291 */ │
│292 │
│293 ssize_t scull_read(struct file *filp, char __user *buf, size_t count, │
│294 loff_t *f_pos) │
B+ │295 { │
│296 struct scull_dev *dev = filp->private_data; │
│297 struct scull_qset *dptr; /* the first listitem */ │
>│298 int quantum = dev->quantum, qset = dev->qset; │
│299 int itemsize = quantum * qset; /* how many bytes in the listitem */ │
│300 int item, s_pos, q_pos, rest; │
│301 ssize_t retval = 0; │
│302 │
│303 if (down_interruptible(&dev->sem)) │
│304 return -ERESTARTSYS; │
│305 if (*f_pos >= dev->size) │
│306 goto out; │
│307 if (*f_pos + count > dev->size) │
│308 count = dev->size - *f_pos; │
│309 │
│310 /* find listitem, qset index, and offset in the quantum */ │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────┘
remote Thread 1 In: scull_read L298 PC: 0x7f000b0c
(gdb) n
Enjoy!
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