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Write protection on SD/QSPI?

rdb98789

I'd like to know if it is possible to make the Microzed "Read Only" in terms of non-volatile memory. That is, the Zynq can still boot from QSPI/SD, but no way for the application SW/FW to write to non-volatile memory. Ideally we'd only allow programming of the QSPI through JTAG. Open to out-of-the-box thinking like board mods.

  • Several questions:

    1. Linux or bare metal.

    If Linux:

    Where is your root (/) directory?  If it is RAM then there *MIGHT* be a device tree entry for the QSPI that tells the driver to do read only accesses.  If not, patch the kernel driver for the QSPI to not allow write access.

    You didn't mention if the OS should be able to write to the QPSI..

    Please expand on your actual requirements.

  • in reply to dyessgg

    Bare metal, no OS. The way I envision it is: Bootloader is programmed into QSPI via JTAG, then we enable write-protect so nothing can ever write to QSPI again. We want the bootloader to perform network booting (both PL firmware and ARM application), so there is a concern that someone may boot with an ARM application that can still access QSPI.

  • in reply to rdb98789

    A quick glance at the schematics shows the QSPI part does not have a write protect pin so that approach is out.

    QSPI doesn't have a "write" signal.  It's part of the protocol.

    I don't have time to check the reference manual for the Zynq 7000 right now.  If I were you, I'd check that document and read the QSPI controller section to see if it has an input to write protect the device.  If it does, tthis might be the easiest path and might not require  a board mod.

    There *MIGHT* be another way.  Check if that part uses one of the upper SPI data lines as a write protect pin when in SPI or DSPI modes.  If it does, you *MIGHT* be able to cut those upper 2 or 3 lines and then jumper the WP pin as needed.  Not something I would want to do.

    If that doesn't work, you might try to find a QSPI device that has a write protect pin and create a small mezzanine bard to solder down to the MicroZED with the new part and a WP jumper on it.  Might not work.

    Last and least, lay out your own MicroZED board with a different part that has a write protect pin.

    Best of luck to you.

  • in reply to dyessgg

    Thanks for the feedback, and the creative idea

  • I am looking at the rev H of the MicroZed board. It has an Infineon S25FL128SAGB QSPI chip.

    The datasheet shows several registers that might be useful for write protection. Chapter 10 talks about data protection. Those are all QSPI commands that set protection bits, which need to be performed after programming. I did not read into details about removing the protection, but this would make it much harder for regular applications to write into the QSPI.