RTnet (UDP) on PREEMPT_RT Linux

Please read the whole doc to have an impression.

Features:

• ported to raspberry pi 4 (bcmgenet), orange pi one (stmmac), realtek (8139too), microchip (enc28j60)
• note: the bbb driver from this repository is not ported to rtnet-preempt_rt, I do not remember exactly why I have included it at that time (2 years ago)
• rtnet UDP socket, bind, recvmsg, sendto, recvfrom, sendmsg, select, poll system calls (the system calls names are appended with _rtnet(), but you can rename them);
• timeout possible for recv;
• sockets with AF_INET (UDP) or AF_PACKET (raw) family;
• rtnetproxy for ssh and scp (but uses RT driver bandwidth)
• also see the help docs in the rtnet-geek repository.
• TODO: port routing, rtcfg, rtmac, tdma and nomac if there will be interest
• improvements can be made around the variable msg_in_userspace, like avoiding multiple packet copies

Paper

• if you use our work, please cite us: L. -C. Duca and A. Duca, "Achieving Hard Real-Time Networking on PREEMPT_RT Linux with RTnet" 2020 International Symposium on Fundamentals of Electrical Engineering (ISFEE), 2020, pp. 1-4, doi: 10.1109/ISFEE51261.2020.9756165.
• https://ieeexplore.ieee.org/document/9756165

0. Download linux-5.9.tar.xz

https://cdn.kernel.org/pub/linux/kernel

1a. Apply patch (includes PREEMPT_RT)

cd linux-5.9
patch -p1 < ../rtnet-v11b-preempt_rt-linux-5.9.patch

1b. Add the _rtnet() system calls

• rpi-4

cp ../rpi-4/unistd.h include/uapi/asm-generic/

• x86_64 qemu

cp ../x86_64/syscall_64.tbl arch/x86/entry/syscalls/

• orangepi-one

cp ../orangepi-one/syscall.tbl arch/arm/tools/

• beaglebone black (patch with bbb rtnet driver including PREEMPT_RT)

cp ../bbb/am335x-bone-common.dtsi arch/arm/boot/dts/
cp ../bbb/syscall.tbl arch/arm/tools/

• microchip enc28j60 on raspberry pi zero (needs RT SPI drivers, see https://github.com/laurentiuduca/real-time-spi)

cp ../rpi-zero-enc28j60/bcm2835-rpi.dtsi arch/arm/boot/dts/
cp ../bbb/syscall.tbl arch/arm/tools/

2. Use buildroot to setup a rootfs for the target board

3. Configure linux

Note for rpi 4 (choose the 64 bits version)

• SSH is disabled by default; can be enabled by creating a file with name "ssh" in boot partition
• cmdline.txt: root=/dev/mmcblk1p2 rootwait console=tty1 console=ttyS1,115200

https://gist.github.com/lategoodbye/c7317a42bf7f9c07f5a91baed8c68f75

https://www.raspberrypi.org/forums/viewtopic.php?t=249579

defconfig

rpi-4

make ARCH=arm64 defconfig

orangepi-one

make ARCH=arm sunxi_defconfig

bbb

make ARCH=arm omap2plus_defconfig

rpi-0

• cmdline.txt: root=/dev/mmcblk0p2 rootwait console=tty1 console=ttyS1,115200

make ARCH=arm bcm2835_defconfig

qemu x86_64

make ARCH=x86_64 x86_64_defconfig

In the kernel configuration, set the following settings as enabled [*] or disabled []

• CONFIG_PREEMPT_RT_FULL: General setup → Preemption Model (Fully Preemptible Kernel (RT)) → Fully Preemptible Kernel (RT) (Depends on: && EXPERT [=y] && ARCH_SUPPORTS_RT [=y] && KVM=[n])

• Enable HIGH_RES_TIMERS: General setup → Timers subsystem → High Resolution Timer Support (Actually, this should already be enabled in the standard configuration.) CONFIG_HZ_PERIODIC=n, CONFIG_NO_HZ=n, CONFIG_NO_HZ_FULL=y

• Kernel features - Processor type and features → [] Multi-core scheduler support (CONFIG_SCHED_MC)

• [] ACPI Support

• Power management and ACPI options / CPU Power Management --->
  CPU Frequency scaling ---> [ ] CPU Frequency scaling
  CPU idle ---> [ ] CPU idle PM support

• rtnet is in the net folder and must compile into kernel its driver (there must be selected in-kernel ipv4, icmp and udp from the protocol stack and proxy as a module):

Select Networking Support - RTnet, 
  Protocol Stack -> (32) Size of central RX-FIFO,
    Real-Time IPv4, ICMP support, (32)  Maximum host routing table entries, 
    UDP support, Real-Time Packet Socket Support.
    The rest must be unselected.
  Drivers -> the driver for the target computer
  Add-Ons -> IP protocol proxy for Linux

• be sure to disable the non-RTnet network drivers from net/ethernet Device Drivers -> Network device support -> Ethernet driver support -> Broadcom, STMicroelectronics devices, TI, etc

4. Compile linux

• x86_64 qemu

make -j5 ARCH=x86_64 INSTALL_MOD_PATH=/home/user/modules CONFIG_DEBUG_INFO=y bzImage modules modules_install

• rpi-4

make -j5 ARCH=arm64 CROSS_COMPILE="..." CONFIG_DEBUG_INFO=y INSTALL_MOD_PATH=/home/laur/lucru/rtnet/modules Image bcm2711-rpi-4-b.dtb modules modules_install

• orangepi-one

make -j5 ARCH=arm CROSS_COMPILE="..." CONFIG_DEBUG_INFO=y INSTALL_MOD_PATH=/home/laur/lucru/rtnet/modules zImage sun8i-h3-orangepi-one.dtb modules modules_install

• bbb

make -j5 ARCH=arm CROSS_COMPILE="..." CONFIG_DEBUG_INFO=y INSTALL_MOD_PATH=/home/laur/lucru/rtnet/modules zImage am335x-boneblack.dtb modules modules_install

• rpi-0

make -j5 ARCH=arm CROSS_COMPILE="..." CONFIG_DEBUG_INFO=y INSTALL_MOD_PATH=/home/laur/lucru/rtnet/modules zImage bcm2835-rpi-zero-w.dtb modules modules_install

5. Boot qemu x86_64 emulator or boot target board

• qemu x86_64 emulator (see x86_64/qemu/config-qemu.txt)

sudo qemu-system-x86_64 -m 1G --enable-kvm -M q35 -kernel bzImage -hda rootfs-50 -append "console=tty1 console=ttyS0 root=/dev/sda rw" -device rtl8139,netdev=bridgeid,mac=52:54:00:11:22:44 -netdev bridge,br=br0,id=bridgeid -serial stdio
sudo qemu-system-x86_64 -m 1G              -M q35 -kernel bzImage -hda rootfs-50 -append "console=tty1 console=ttyS0 root=/dev/sda rw" -device rtl8139,netdev=bridgeid,mac=52:54:00:11:22:44 -netdev bridge,br=br0,id=bridgeid -serial stdio
with empty password (ENTER).

6. After booting qemu or target, read start-modules.sh (a better name would be setup-rtnet.sh)

• on the target:

./start-modules.sh:

which equivalates to

set -x
mount -t debugfs debugfs /sys/kernel/debug
/root/rtifconfig rteth0 up 192.168.1.70
## now you should wait for the interface to be set up
/root/rtifconfig rtlo up 127.0.0.1
ifconfig rtproxy up 192.168.1.70
/root/rtroute solicit 192.168.1.30 dev rteth0
/root/rtroute solicit 192.168.1.40 dev rteth0
/root/rtroute solicit 192.168.1.50 dev rteth0
/root/rtroute solicit 192.168.1.60 dev rteth0

• on the development host:

ping 192.168.1.70

7. There are provided tftp client (both x86_64 and arm) and server (for x86_64).

If you do not use rtnetproxy for scp or ssh, you can use tftp.
On the development host:

cp zImage /tmp/
./tftpd -d -P 8086

On the target, to get zImage:

./tftpc 192.168.1.100 -P 8086 -g zImage -o

On the target, to copy to server:

./tftpc 192.168.1.100 -P 8086 -p filename -o

You will find filename in /tmp

8. Testing

Please read rtt-laur.c and rtt-sender.c/rtt-responder.c for UDP sockets and raw_recv.c and raw_send.c for raw sockets.

8a. Hello world

on one computer:

./rtt-laur.out

on another computer

./rtt-laur.out -d 192.168.1.20

8b. Test RTT

On one computer

./rtt-responder.out

on another computer

./rtt-sender -d 192.168.1.20

8.c. Test raw sockets

On one computer

./raw_recv

on another computer

./raw_send

Success,
laurentiu [dot] duca [at] gmail [dot] com