Announcing a tool for Armada 3720 firmware

Marek Behun marek.behun at
Mon Jun 14 17:11:56 CEST 2021


this is announcement of mox-imager [1], a firmware uploader / manipulator
for Marvell's Armada 3720 SOC.

For most of you who use the SOC on boards other than Turris MOX, the
most useful feature probably is that it can upload a firmware via UART
at higher baudrates than Marvell's original WtpDownloader, which is
useful when debugging or during board manufacture.

Features that should be interesting for you:

- ability to upload firmware over UART at baudrates up to 6 MBaud.
  This was tested on ESPRESSObin, but should also work on other boards
  (uDPU, ESPRESSObin Ultra)

  Uploading at 3 MBaud:
  $ ./mox-imager -b 3000000 -D /dev/ttyUSB0 flash-image.bin

- ability to upload flash-image.bin firmware over UART

  When TF-A builds for A3720, it creates image for SPI/eMMC called
  flash-image.bin, and a directory uart-images containing 3 binaries
  that you have to use instead of flash-image.bin if you want to boot
  via UART.

  mox-imager can work with both methods. When given flash-image.bin,
  it updates BootFlashSign in the TIM header so that the BootROM will
  accept the image when given over UART.

  So both of these work:
  $ ./mox-imager -D /dev/ttyUSB0 flash-image.bin
  $ ./mox-imager -D /dev/ttyUSB0 TIM_ATF.bin wtmi_h.bin boot-image_h.bin

  (This of course does not work if the image needs to be signed
   cryptographically and the singing key is not present. But AFAIK only
   Turris MOX uses this feature of the SOC.)

- mox-imager has an implementation of a mini-terminal (code from
  U-Boot's kwboot), which can be used instead of minicom/kermit, once
  the firmware is uploaded. Although this mini-terminal does not support
  uploading images over Y-MODEM or other protocols to U-Boot, it can
  still be useful. If not for anything else, then at least for the
  ability to not lose any output which the SOC might have sent over
  UART. (When using minicom/kermit, there is a small window when the
  /dev/ttyX device is closed and some output is lost.) Use the -t flag
  to invoke this mini-terminal.

Other features that we use on Turris MOX and may be useful to you, but
need implementation for your boards:

- we use one firmware image for all versions of our board:
  DDR3 512 MiB, DDR3 1024 MiB, DDR4

  This simplifies development of updates significantly.

  We achieve this by burning board version info into the SOC's OTP.
  The GPP code contained in the TIM header can read OTP and decide how
  to initialize clock and DDR registers depending on the values there.

  The GPP code also works when OTP is empty. In that case it first tries
  to initialize the registers for DDR3, tests if DDR works, and if not,
  switches to DDR4. Then it determines RAM size. Note that we do not use
  this method in production, this was only tested on a few boards that
  we use for development. (We do not know for example, whether it is
  safe for the DDR4 chip if we first try to communicate with it in DDR3
  mode, since the protocols are different.)

  You can look at the GPP code at

- mox-imager can create trusted firmware image signed with ECDSA
  signature and can write the SOC's OTP so that only images signed
  with a specific ECDSA key will boot. We use this on Turris MOX.

Related software:

- we have significantly modified Marvell's original WTMI firmware that
  runs on the Cortex-M3 secure coprocessor. You can look at this
  modified firmware at our mox-boot-builder repository [2] in directory

  Perhaps the most interesting feature for you is that this firmware
  exposes the SOC's internal HW RNG via the mailbox to Linux, and that
  upstream Linux has a driver (turris-mox-rwtm) that registers this
  random number generator via Linux' crypto API.

  Another feature our firmware supports is that it can utilize the
  crypto engine in the secure processor for creating ECDSA signatures.
  Every Turris MOX has an ECDSA key generated and burned into OTP when
  manufactured. When done correctly, it is impossible to read this key.
  It is only possible to use it via the crypto engine for ECDSA
  signatures. (The firmware has to be in trusted mode for this. If the
  user has the ability to upload any firmware into their device, they
  can read the private key from OTP.)

  This firmware can be built as a standalone replacement of Marvell's
  WTMI firmware from A3700-utils-marvell repository, but also as an
  wtmi_app.bin payload application for Marvell's firmware (in this case
  DDR and clocks are initialized by Marvell's code and HW RNG is
  provided by wtmi_app.bin).
  There are instructions on how to use this firmware on ESPRESSObin in

- turris-mox-rwtm driver in Linux [3] communicates with our WTMI
  firmware (see the point above) and exposes to Linux:
  - the SOC's HWRNG
  - the SOC's ECDSA signing engine with singing key stored in OTP.
    This can be used for authorizing the device, for example via SSH
  - OTP rows containing Turris MOX' serial number, board version and
    MAC address

  I'm thinking about implementing code into this driver so that it will
  also work with Marvell's original firmware, which only exposes access
  to OTP memory.

- mox-pkcs11 [4] is a plugin for ssh that can utilize the HW ECDSA
  signing mechanism mentioned above when connecting to an ssh server

Let us know if you are interested in any of these or need help with

Marek & Pali


    The name should probably be something like a3720-tool, but
    I called it mox-imager at the beginning because then it was meant
    to be used only for Turris MOX.




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