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cdc-acm-usbdriver.md

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TL;DR Zigbee kernel module for Terramaster F4-210 NAS

  • Enable ssh access on your NAS
  • Connect to your NAS through ssh
  • Start root session: sudo su - and enter your password to gain root access (shell prompt must change from $ to #)
  • Download this module and put it into /lib/modules/4.4.18-g8bcbd8a-dirty: ter_wget _TBD_ -O /lib/modules/4.4.18-g8bcbd8a-dirty/cdc-acm.ko.
  • Install module by applying command modprobe cdc-acm. If everything is ok then nothing is printed. If your stick is plugged then new device appears ls -l /dev/ttyACM0. And in this case you are ready to run zigbee2mqtt.
  • If anything goes wrong you get the following message
1 module could not be probed
- cdc-acm

In order to find out the reason you have to check kernel messages by applying command dmesg -T.

Instructions to build cdc-acm usb driver for terramaster F4-210 NAS

  • This is applicable only for Linux or any other system that can run make for linux kernel (e.g. cygwin or MacOS). In order to build module you need several dependencies installed (most probably m4, autoconf, automake, libtool, make, g++, gpp). Another solution is to run the whole thing in docker - e.g. sinovoip/bpi-build-linux:
    • docker pull sinovoip/bpi-build-linux-4.4:ubuntu16.04
    • docker run -it --rm -v _local_src_path_:/usr/src -v _local_toolchain_path_:/usr/toolchain sinovoip/bpi-build-linux-4.4:ubuntu16.04
  • Download 4.4.8 kernel sources from here and unpack (tar -xvf linux-4.4.18.tar.gz)
  • Download patch, change current current dir to linux-4.4.18/ - cd linux-4.4.18 and apply patch < /path/to/downloaded/patch/file. This applies patch to rename __copy_to_user -> __arch_copy_to_user and adds ARCH_RTD129x platfrom support into arch/arm64/Kconfig.platforms
  • Run make menuconfig to create default config, exit, save it and then run make ARCH=x86_64 scripts to create build scripts. If you see error: code model kernel does not support PIC mode during compilation then check Apply PIC patch section
  • Put arm64 config into linux-4.4.18/ dir
  • Download aarch64 toolchain. In order to use appropriate toolchain you have to provide prefix either by applying CROSS_COMPILE=_prefix_ parameter to make or specifying CONFIG_CROSS_COMPILE parameter in .config. If your toolchain is in PATH you can specify just prefix - e.g. aarch64-linux-gnu- for gcc-aarch64-linux-gnu or with full path e.g. /opt/toolchains/aarch64-linaro/bin/aarch64-linux-gnu-.
    • Initially I've tried gcc-aarch64-linux-gnu from my current ubuntu distribution (Ubuntu 21.04). Install it by applying sudo apt-get install --install-recommends gcc-aarch64-linux-gnu and use aarch64-linux-gnu- cross compile prefix.
    • Linaro. I assume in order to compile on x86_64 host you have to download x86_64 Linux hosted cross compilers -> AArch64 GNU/Linux target (aarch64-none-linux-gnu)
    • I used Linaro GCC 7.3-2018.05 from the raspberry pi BPI-W2-bsp - check toolchains/gcc-linaro-7.3.1-2018.05-x86_64_aarch64-linux-gnu/bin dir.
  • Run make ARCH=arm64 [CROSS_COMPILE=_gcc-prefix_] prepare
  • Run make ARCH=arm64 [CROSS_COMPILE=_gcc-prefix_] M=drivers/usb/class to build driver. If everything is ok your driver will be located in drivers/usb/class/cdc-acm.ko.

Apply PIC patch

This step is needed if you see error like this: code model kernel does not support PIC mode during make phase. There is an issue - kernel doesn't support PIC mode for compiling. This is applicable for gcc 6+ versions where PIE (position independent executables) is enabled by default. In order to fix apply this makefile patch.

Zigbee and default NAS kernel

I have zigbee texas instruments cc2531 based stick to run my home assistant. Use homeassistant as a core, zigbee2mqtt as zigbee stick driver, mosquitto as mqtt broker - channel between homeassistant and zigbee2mqtt. In order to support zigbee cc2531 stick and run zigbee2mqtt we need cdc-acm usb driver. Driver is present in main kernel source. But during kernel compilation I've found that there is incongruity. I've asked question on stack overflow with detailed description.

So the problem is: Using cdc-acm compiled against kernel 4.4.8 reported the following error:

cdc_acm: Unknown symbol __copy_to_user (err 0)
cdc_acm: Unknown symbol __copy_from_user (err 0)

And current NAS kernel instead contains:

# cat /proc/kallsyms | grep copy_to_user
ffffff80082923f0 T copy_to_user_page
ffffff80087d2600 T __arch_copy_to_user

I googled for __arch_copy_to_user and found that it was introduced in kernel 4.8.

But on the other hand kernel 4.8 also introduced moving function cdc_parse_cdc_header to drivers/usb/core/message.c from drivers/net/usb/usbnet.c And our kernel doesn't have it.

So looks like current NAS kernel source is a mix of different kernel versions. So in order to get working cdc-acm driver I had to modify kernel sources manually.

Also I added ARCH_RTD129x by applying arch/arm64/Kconfig.platforms value from newer build.

Note: I will try to ask Terramaster about providing kernel sources they used to build firmware. At the end they have to provide sources since they are licensed by GNU GPL.

Kernel configuration

Here is list of parameters I changed:

  • Platform selection -> Realtek RTD129x SoC Family
  • Enable loadable module support -> [-] Module versioning support (because our kernel doesn't have it)
  • Kernel hacking -> [-] Tracers (because otherwise _mcount() function is used and our kernel doesn't have it)
  • Kernel Features -> Preemption Model -> No Forced Preemption (Server) (because our kernel doesn't have it)
  • Local version -> -g8bcbd8a-dirty