Colibri IMX6 IMX7 boot configuration from external NOR flash vs NAND


We are considering using the Colibri iMX7S/D or the IMX6ULL in our design, which has an expected lifetime of 30 years.

We anticipate problems if we let the system boot from the NAND flash on the SOM (due to read-distrub issues/NAND flash unreliablity). Hence we were looking into the possibility to let the module boot from an external NOR flash chip.

From the datasheets, it seems that it is only possible to change 1 boot parameter: Either to boot from SOM NAND or external SD memory. The NXP processors support booting from SPI NOR flash though.

The question:

  • Is there a way to let the colibri modules boot from SPI nor flash?
  • Are the fuses on the processors preburnt or is this flexible?
  • What is the expected lifetime/ boots when booting from the embedded SLC NAND flash?

Thanks for your reply!

Kind regards,

Hi @Arnout

Unfortunately, the of-the-shelf Colibri module cannot boot from SPI NOR flash. We need to fuse the modules for booting from the on-module NAND or eMMC drive. Theoretically what would be possible is to boot only U-Boot from the on-module drive and then jump into an operating system located on NOR flash. The main problem for NAND flash are the limited write cycles. If you have only the boot rom (U-Boot) in the NAND, it is less likely that flash fails over time.

It is hard to estimate the lifetime expectation of SLC NAND. A normal guaranteed value is 100k write cycles. Unfortunately, I do not know the number of read cycles, but it is much higher. The actual lifetime of NAND also depends on wear leveling algorithm. The algorithm makes sure the files are not written always at the same location.