Time Sensitive Networking (TSN) is a collection of Ethernet standards defined by IEEE 802.1Q that enables deterministic messaging over standard Ethernet networks. With TSN, Ethernet frames are not limited to Internet Protocol, so it can carry the payload of any industrial application.

Enable TSN support

To add TSN support and tools to your system, add the feature to your project’s conf/local.conf file:

conf/local.conf
# TSN
DISTRO_FEATURES:append = " tsn"

Rebuild your image, for example:

$ bitbake dey-image-qt

Deploy the resulting images to the device.

Kernel configuration

You can manage the Ethernet driver and PHY device support through the following kernel configuration options:

  • 802.1 Time-Sensitive Networking support (CONFIG_TSN)

  • ENETC PF driver (CONFIG_FSL_ENETC)

  • ENETC hardware Time-sensitive Network support (CONFIG_FSL_ENETC_QOS)

These options are enabled as built-in on the default ConnectCore 93 kernel configuration file.

IEEE 802.1 Standard configuration

The Linux ecosystem supports several TSN features such as Credit-Based Shaper (formerly Qav), Enhancements for Scheduled Traffic (EST, former Qbv), Generalized Precision Time Protocol (gPTP), and Audio/Video Transport Protocol (AVTP). You can manage the different TSN standards through the following kernel configuration options:

  • Hardware Multiqueue-aware Multi Band Queuing (MULTIQ) (CONFIG_NET_SCH_MULTIQ)

  • Credit Based Shaper (CBS) (CONFIG_NET_SCH_CBS)

  • Earliest TxTime First (ETF) (CONFIG_NET_SCH_ETF)

  • Time Aware Priority (taprio) Scheduler (CONFIG_NET_SCH_TAPRIO)

  • Multi-queue priority scheduler (MQPRIO) (CONFIG_NET_SCH_MQPRIO)

  • Elementary classification (BASIC) (CONFIG_NET_CLS_BASIC)

  • Flower classifier (CONFIG_NET_CLS_FLOWER)

  • Generic actions (CONFIG_NET_ACT_GACT)

  • Redirecting and Mirroring (CONFIG_NET_ACT_MIRRED)

  • Frame gate entry list control tc action (CONFIG_NET_ACT_GATE)

These options are not enabled in the default defconfig, but they are added via a config fragment when you enable TSN support in your Digi Embedded Yocto project.

Many more configuration options are available. You must include or exclude options based on your final application.

Kernel driver

The drivers for the i.MX93 TSN Ethernet support are located at:

File Description

drivers/net/ethernet/freescale/enetc/enetc_tsn.c

ENETC PF driver

drivers/net/ethernet/freescale/enetc/enetc_qos.c

ENETC hardware Time-sensitive Network

Device tree bindings and customization

The i.MX93 Ethernet interface device tree binding is documented at Documentation/devicetree/bindings/net/snps,dwmac.yaml. The Ethernet interface is defined in the i.MX93 CPU and ConnectCore 93 Development Kit device tree files.

Enable remaining EQoS driver Ethernet queues

All five queues are required for TSN support. Digi provides a pre-compiled device tree overlay to enable these remaining queues that are necessary for TSN support, and that are otherwise disabled on the default device tree. To apply this overlay, run the following command in U-Boot:

=> setenv overlays ccimx9-dvk_eqos-tsn.dtbo,${overlays}
=> saveenv

TSN user space

TSN user space tools

After enabling TSN support, Digi Embedded Yocto includes several tools into the rootfs to configure the TSN connection on the target. The following tools are available in user space.

  • ptp4l: Daemon that synchronizes the PTP Hardware Clock (PHC) from the NIC.

  • phc2sys: Daemon that synchronizes the PHC and the system clock.

  • pmc: Utility tool to configure ptp4l in run-time.

  • tc: Traffic Control (TC) subsystem that helps police, classify, shape, and schedule network traffic and manages packet content.

TSN user space usage

The test consists on two devices connected through a direct cable or through a TSN switch, one acting as master and the other as slave.a The test consists of two devices—one acting as master and the other as slave—connected through a direct cable or through a TSN switch.

  1. Check hardware timestamp support

    # ethtool -T eth0 | grep PTP
PTP Hardware Clock: 0

  2. Set up server script (server.sh)

    #!/bin/sh
echo "[SERVER] Configuring PTP Server on eth0"

tc qdisc del dev eth0 root 2>/dev/null

tc qdisc add dev eth0 root handle 100 taprio \
    num_tc 1 map 0 queues 1@0 \
    base-time 0 \
    sched-entry S 01 1000000 \
    flags 0x2

ptp4l -i eth0 -f /etc/linuxptp/ptp4l.conf -m -s

  3. Set up client script (client.sh)

    #!/bin/sh
echo "[CLIENT] Configuring PTP Client on eth0"

tc qdisc del dev eth0 root 2>/dev/null

tc qdisc add dev eth0 root handle 100 taprio \
    num_tc 1 map 0 queues 1@0 \
    base-time 0 \
    sched-entry S 01 1000000 \
    flags 0x2

ptp4l -i eth0 -f /etc/linuxptp/ptp4l.conf -m &
sleep 2
phc2sys -s eth0 -c CLOCK_REALTIME -O 0 -m

  4. Run on the server side

    # chmod +x server.sh
# ./server.sh
[SERVER] Configuring PTP Server on eth0
[  312.614080] imx-dwmac 428a0000.ethernet eth0: disabled FPE
[  312.619629] imx-dwmac 428a0000.ethernet eth0: stop FPE handshake
[  312.631960] imx-dwmac 428a0000.ethernet eth0: configured EST
[  312.637630] imx-dwmac 428a0000.ethernet eth0: EST: SWOL has been switched
Warning: sch_taprio: Size table not specified, frame length estimations may be inaccurate.
ptp4l[312.643]: selected /dev/ptp0 as PTP clock
ptp4l[312.645]: port 1 (eth0): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[312.645]: port 0 (/var/run/ptp4l): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[312.645]: port 0 (/var/run/ptp4lro): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[319.566]: selected local clock 0004f3.fffe.73330a as best master
ptp4l[322.792]: port 1 (eth0): new foreign master 0004f3.fffe.290020-1
ptp4l[326.792]: selected best master clock 0004f3.fffe.290020
ptp4l[326.792]: port 1 (eth0): LISTENING to UNCALIBRATED on RS_SLAVE
ptp4l[328.791]: master offset        408 s0 freq   -3411 path delay      3018
ptp4l[329.791]: master offset        389 s2 freq   -3430 path delay      3053
ptp4l[329.792]: port 1 (eth0): UNCALIBRATED to SLAVE on MASTER_CLOCK_SELECTED
ptp4l[330.792]: master offset        202 s2 freq   -3228 path delay      3088

  5. Run on the client side

    # chmod +x client.sh
# ./client.sh
[CLIENT] Configuring PTP Client on eth0
[  154.821990] imx-dwmac 428a0000.ethernet eth0: disabled FPE
[  154.827502] imx-dwmac 428a0000.ethernet eth0: stop FPE handshake
[  154.839492] imx-dwmac 428a0000.ethernet eth0: configured EST
[  154.839769] imx-dwmac 428a0000.ethernet eth0: EST: SWOL has been switched
Warning: sch_taprio: Size table not specified, frame length estimations may be inaccurate.
ptp4l[154.851]: selected /dev/ptp0 as PTP clock
ptp4l[154.852]: port 1 (eth0): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[154.853]: port 0 (/var/run/ptp4l): INITIALIZING to LISTENING on INIT_COMPLETE
ptp4l[154.853]: port 0 (/var/run/ptp4lro): INITIALIZING to LISTENING on INIT_COMPLETE
phc2sys[157.855]: CLOCK_REALTIME phc offset       147 s0 freq     -27 delay    583
phc2sys[158.855]: CLOCK_REALTIME phc offset       164 s2 freq     -10 delay    583
phc2sys[159.856]: CLOCK_REALTIME phc offset       206 s2 freq    +196 delay    583
phc2sys[160.856]: CLOCK_REALTIME phc offset       -21 s2 freq     +31 delay    583
phc2sys[161.856]: CLOCK_REALTIME phc offset       -43 s2 freq      +3 delay    583
ptp4l[162.164]: port 1 (eth0): LISTENING to MASTER on ANNOUNCE_RECEIPT_TIMEOUT_EXPIRES
ptp4l[162.165]: selected local clock 0004f3.fffe.290020 as best master
ptp4l[162.165]: port 1 (eth0): assuming the grand master role
phc2sys[162.856]: CLOCK_REALTIME phc offset       -35 s2 freq      -2 delay    583

  6. Optionally validate TSN Qdisc (on either board)

    # tc qdisc show dev eth0
qdisc taprio 100: root tc 1 map 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
queues offset 0 count 1
 flags 0x2      base-time 0 cycle-time 1000000 cycle-time-extension 0
        index 0 cmd S gatemask 0x1 interval 1000000
max-sdu 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
fp E E E E E E E E E E E E E E E E

qdisc pfifo 0: parent 100:1 refcnt 2 limit 1000p