Running TCP/IP Stack in Linux

With uClinux running on the i.MX RT1024, you get the full Linux TCP/IP stack. Userspace POSIX APIs are provided by the uClibc library. Key user-space networking tools and utilities are available from the multi-call busybox. Additional tools and packages, such as for instance the SSH dropbear server, can be built specifically for uClinux. All in all, you have the powerful Linux TCP/IP stack at your disposal.

There is a full-functioning Ethernet device driver available in the kernel tree for the i.MX RT1024. The device driver is linux/drivers/net/ethernet/freescale/fec.c configured in the kernel using the CONFIG_FEC build time option in Device Drivers -> Network device support -> Ethernet driver support -> Freescale devices -> FEC ethernet controller (of ColdFire and some i.MX CPUs).

For the run-time configuration of the kernel, Ethernet is enabled in rootfs.dts.IMXRT102X_NXPEVK in projects/rootfs as follows:

 &fec {
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_fec>;
        status = "okay";

        assigned-clocks = <&clks IMXRT1020_CLK_ENET_REF>, 
        <&clks IMXRT1020_CLK_PLL6_BYPASS>;
        assigned-clock-rates = <50000000>;
        assigned-clock-parents = <0>, <&clks IMXRT1020_CLK_PLL6>;

        clocks = <&clks IMXRT1020_CLK_ENET>,
                 <&clks IMXRT1020_CLK_AHB_PODF>,
                 <&clks IMXRT1020_CLK_ENET_REF>;
        clock-names = "ipg", "ahb", "enet_clk_ref";
        fsl,ref-clk-dir = <&gpr 4 17 1>;

        phy-mode = "rmii";
        phy-handle = <&ethphy0>;
        phy-reset-duration = <1>;
        phy-reset-gpios = <&gpio1 4 GPIO_ACTIVE_LOW>;

        mdio {
                #address-cells = <1>;
                #size-cells = <0>;

                ethphy0: ethernet-phy@0 {
                        reg = <2>;
                        clocks = <&clks IMXRT1020_CLK_ENET_REF>;
                        clock-names = "rmii-ref";
                };
        };
};

This will register a platform device for the i.MX RT1024 Ethernet controller with the Ethernet driver.

The Linux project provided by Emcraft in the distribution (refer to projects/rootfs) and installed on each shipping module and kit includes the TCP/IP stack and various network related capabilities. The following snapshot shows the full Linux bootstrap sequence from power-on to the Linux shell:

U-Boot SPL 2022.04 (Jul 03 2023 - 09:52:07 +0000) Trying to boot from MMC1 U-Boot 2022.04 (Jul 03 2023 - 09:52:07 +0000) DRAM: 32 MiB Core: 59 devices, 13 uclasses, devicetree: separate MMC: FSL_SDHC: 0 Loading Environment from MMC... OK In: serial@40184000 Out: serial@40184000 Err: serial@40184000 Net: eth0: ethernet@402D8000 Hit any key to stop autoboot: 0 6940407 bytes read in 671 ms (9.9 MiB/s) ## Booting kernel from Legacy Image at 80007fc0 ... Image Name: Linux-5.15.71 Image Type: ARM Linux Multi-File Image (uncompressed) Data Size: 6940343 Bytes = 6.6 MiB Load Address: 80008000 Entry Point: 80008001 Contents: Image 0: 6934720 Bytes = 6.6 MiB Image 1: 5611 Bytes = 5.5 KiB Verifying Checksum ... OK ## Flattened Device Tree from multi component Image at 80007FC0 Booting using the fdt at 0x806a50cc Loading Multi-File Image Loading Device Tree to 81d83000, end 81d875ea ... OK Starting kernel ... Booting Linux on physical CPU 0x0 Linux version 5.15.71 (sasha@workbench.emcraft.com) (arm-none-eabi-gcc (GNU Arm Embedded Toolchain 10.3-2021.10) 10.3.1 20210824 (release), GNU ld (GNU Arm Embedded Toolchain 10.3-2021.10) 2.36.1.20210621) #2 Sun Jul 2 06:58:16 UTC 2023 CPU: ARMv7-M [411fc271] revision 1 (ARMv7M), cr=00000000 CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache OF: fdt: Machine model: NXP IMXRT1024 EVK board Reserved memory: created DMA memory pool at 0x81f00000, size 1 MiB OF: reserved mem: initialized node dmapool@81f00000, compatible id shared-dma-pool Zone ranges: Normal [mem 0x0000000080000000-0x0000000081ffffff] Movable zone start for each node Early memory node ranges node 0: [mem 0x0000000080000000-0x0000000081efffff] node 0: [mem 0x0000000081f00000-0x0000000081ffffff] Initmem setup node 0 [mem 0x0000000080000000-0x0000000081ffffff] Built 1 zonelists, mobility grouping off. Total pages: 8128 Kernel command line: clk_ignore_unused ip=192.168.88.89:192.168.88.170:192. 168.88.1:255.255.0.0::eth0:off Unknown kernel command line parameters "ip=192.168.88.89:192.168.88.170:192. 168.88.1:255.255.0.0::eth0:off", will be passed to user space. Dentry cache hash table entries: 4096 (order: 2, 16384 bytes, linear) Inode-cache hash table entries: 2048 (order: 1, 8192 bytes, linear) mem auto-init: stack:off, heap alloc:off, heap free:off Memory: 24532K/32768K available (3266K kernel code, 180K rwdata, 860K rodata, 2264K init, 97K bss, 8236K reserved, 0K cma-reserved) NR_IRQS: 16, nr_irqs: 16, preallocated irqs: 16 Switching to timer-based delay loop, resolution 333ns sched_clock: 32 bits at 3000kHz, resolution 333ns, wraps every 715827882841ns clocksource: mxc_timer1: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 637086815595 ns Calibrating delay loop (skipped), value calculated using timer frequency.. 6.00 BogoMIPS (lpj=30000) pid_max: default: 4096 minimum: 301 Mount-cache hash table entries: 1024 (order: 0, 4096 bytes, linear) Mountpoint-cache hash table entries: 1024 (order: 0, 4096 bytes, linear) devtmpfs: initialized DMA: default coherent area is set clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns futex hash table entries: 16 (order: -5, 192 bytes, linear) pinctrl core: initialized pinctrl subsystem NET: Registered PF_NETLINK/PF_ROUTE protocol family imxrt1020-pinctrl 401f8000.pinctrl: initialized IMX pinctrl driver imxrt1020-pinctrl 400a8000.pinctrl-snvs: initialized IMX pinctrl driver SCSI subsystem initialized usbcore: registered new interface driver usbfs usbcore: registered new interface driver hub usbcore: registered new device driver usb pps_core: LinuxPPS API ver. 1 registered pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it> PTP clock support registered Bluetooth: Core ver 2.22 NET: Registered PF_BLUETOOTH protocol family Bluetooth: HCI device and connection manager initialized Bluetooth: HCI socket layer initialized Bluetooth: L2CAP socket layer initialized Bluetooth: SCO socket layer initialized clocksource: Switched to clocksource mxc_timer1 NET: Registered PF_INET protocol family IP idents hash table entries: 2048 (order: 2, 16384 bytes, linear) tcp_listen_portaddr_hash hash table entries: 512 (order: 0, 4096 bytes, linear) Table-perturb hash table entries: 65536 (order: 6, 262144 bytes, linear) TCP established hash table entries: 1024 (order: 0, 4096 bytes, linear) TCP bind hash table entries: 1024 (order: 0, 4096 bytes, linear) TCP: Hash tables configured (established 1024 bind 1024) UDP hash table entries: 256 (order: 0, 4096 bytes, linear) UDP-Lite hash table entries: 256 (order: 0, 4096 bytes, linear) NET: Registered PF_UNIX/PF_LOCAL protocol family RPC: Registered named UNIX socket transport module. RPC: Registered udp transport module. RPC: Registered tcp transport module. RPC: Registered tcp NFSv4.1 backchannel transport module. Bus freq driver module loaded Initialise system trusted keyrings workingset: timestamp_bits=30 max_order=13 bucket_order=0 fuse: init (API version 7.34) Key type asymmetric registered Asymmetric key parser 'x509' registered Block layer SCSI generic (bsg) driver version 0.4 loaded (major 251) io scheduler mq-deadline registered io scheduler kyber registered 40184000.serial: ttyLP0 at MMIO 0x40184010 (irq = 20, base_baud = 1250000) is a FSL_LPUART fsl-lpuart 40184000.serial: Serial: Console lpuart rounded baud ratefrom 208333 to 115200 printk: console [ttyLP0] enabled PPP generic driver version 2.4.2 PPP BSD Compression module registered PPP Deflate Compression module registered usbcore: registered new interface driver rt2800usb ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver usbcore: registered new interface driver cdc_acm cdc_acm: USB Abstract Control Model driver for USB modems and ISDN adapters usbcore: registered new interface driver uas usbcore: registered new interface driver usb-storage udc-core: couldn't find an available UDC - added [g_serial] to list of pending drivers i2c_dev: i2c /dev entries driver usbcore: registered new interface driver btusb sdhci: Secure Digital Host Controller Interface driver sdhci: Copyright(c) Pierre Ossman sdhci-pltfm: SDHCI platform and OF driver helper usbcore: registered new interface driver usbhid usbhid: USB HID core driver NET: Registered PF_PACKET protocol family sdhci-esdhc-imx 402c0000.esdhc: could not get pinctrl mmc0 bounce up to 128 segments into one, max segment size 65536 bytes Bluetooth: RFCOMM TTY layer initialized Bluetooth: RFCOMM socket layer initialized Bluetooth: RFCOMM ver 1.11 Loading compiled-in X.509 certificates ci_hdrc ci_hdrc.0: EHCI Host Controller ci_hdrc ci_hdrc.0: new USB bus registered, assigned bus number 1 ci_hdrc ci_hdrc.0: USB 2.0 started, EHCI 1.00 hub 1-0:1.0: USB hub found mmc0: SDHCI controller on 402c0000.esdhc [402c0000.esdhc] using DMA hub 1-0:1.0: 1 port detected input: gpio-keys as /devices/platform/gpio-keys/input/input0 cfg80211: Loading compiled-in X.509 certificates for regulatory database cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7' clk: Not disabling unused clocks platform regulatory.0: Direct firmware load for regulatory.db failed with error -2 cfg80211: failed to load regulatory.db Freeing unused kernel image (initmem) memory: 2264K This architecture does not have kernel memory protection. Run /init as init process init started: BusyBox v1.24.2 (2023-07-02 06:58:01 UTC) mmc0: host does not support reading read-only switch, assuming write-enable [70] Jan 01 00:00:01 Running in background mmc0: new SDHC card at address 0001 / # mmcblk0: mmc0:0001 00000 7.37 GiB mmcblk0: p1 Micrel KSZ8081 or KSZ8091 402d8000.ethernet-1:02: attached PHY driver (mii_bus:phy_addr=402d8000.ethernet-1:02, irq=POLL) fec 402d8000.ethernet eth0: Link is Up - 100Mbps/Full - flow control off / #

Let's test the TCP/IP stack on the i.MX RT1024.

From the development host validate that the i.MX RT1024 is visible using ping:

$ ping 192.168.88.89 -c 5
PING 192.168.88.89 (192.168.88.89) 56(84) bytes of data.
64 bytes from 192.168.88.89: icmp_seq=1 ttl=63 time=5.51 ms
64 bytes from 192.168.88.89: icmp_seq=2 ttl=63 time=5.10 ms
64 bytes from 192.168.88.89: icmp_seq=3 ttl=63 time=3.99 ms
64 bytes from 192.168.88.89: icmp_seq=4 ttl=63 time=10.8 ms
64 bytes from 192.168.88.89: icmp_seq=5 ttl=63 time=7.08 ms

--- 192.168.88.89 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4005ms
rtt min/avg/max/mdev = 3.986/6.488/10.773/2.360 ms
$

ping the development host from the i.MX RT1024:

/ # ping -c5 192.168.88.177
PING 192.168.88.177 (192.168.88.177): 56 data bytes
64 bytes from 192.168.88.177: seq=0 ttl=64 time=2.310 ms
64 bytes from 192.168.88.177: seq=1 ttl=64 time=4.518 ms
64 bytes from 192.168.88.177: seq=2 ttl=64 time=2.256 ms
64 bytes from 192.168.88.177: seq=3 ttl=64 time=3.548 ms
64 bytes from 192.168.88.177: seq=4 ttl=64 time=2.508 ms

--- 192.168.88.177 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 2.256/3.028/4.518 ms
/ #

On the target, start the telnetd daemon to allow connections to the i.MX RT1024:

 / # ps | grep telnetd
   96 root       388 S    {busybox} telnetd
  101 root       388 S    grep telnetd
/ #

Connect to the target from the development host using telnet. The target is configured to accept the 123 password for root

$ telnet 192.168.88.89 Trying 192.168.88.89... Connected to 192.168.88.89. Escape character is '^]'. (none) login: root Password: / # ls bin etc httpd lib proc sbin tmp var dev hello.ko init mnt root sys usr / # exit Connection closed by foreign host. $

The dropbear SSH daemon starts automatically on the target. Verify that dropbear allows secure connections to the target:

/ # ps | grep dropbear 70 root 416 S dropbear -R 98 root 388 S grep dropbear

Connect to the target from the development host using ssh. The first connection takes several seconds to establish as the i.MX RT1024 runs computation-extensive key calculations. Again, enter 123 on the password prompt:

$ ssh root@192.168.88.89 
root@192.168.88.89's password: 
/ # ls 
bin       etc       httpd     lib       proc      sbin tmp       var 
dev       hello.ko  init      mnt       root      sys       usr 
# exit
Connection to 192.168.88.89closed.
$

On the target, enable access to the Internet by configuring a default gateway. Note also that the system makes use of the public name server provided by Google:

/ # route add default gw 192.168.88.1
/ # cat /etc/resolv.conf
# This configuration makes use of the Google public DNS server.
# If you would like to use something else, replace with the IP
# of your DNS server

nameserver 8.8.8.8
/ #

Use ntpd to synchronize the time on the target with the time provided by a public server:

/ # date Thu Jan 1 00:32:53 UTC 1970 / # ntpd -p 0.fedora.pool.ntp.org / # sleep 5 / # date Tue Jul 4 10:02:37 UTC 2023

Use wget to download a file from a remote server:

/ # wget ftp://ftp.gnu.org/README Connecting to ftp.gnu.org (209.51.188.20:21) README 100% |*******************************| 2748 0:00:00 ETA / # / # cat README

This is ftp.gnu.org, the FTP server of the the GNU project. ...

Mount a directory exported by a development host over NFS:

/ # mount -o nolock 192.168.88.177:/mnt/nfs_share /mnt/nfs/ / # ls /mnt/nfs/

arm-v7-linux-uclibceabi-pthreads-20181123.tar.bz2 .....

Start the HTTP daemon:

/ # httpd -h /httpd/html/

From a local host, open a Web browser to the i.MX RT1024 and watch the demo web page provided by the target. The i.MX RT1024 shows the current time and date as well as the list of the currently running processes:

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