we are trying to configure our module in way that it can survive temporary external clock (crystal) malfunction. I looks that solution may be using following two measures together:
CMU_OLR bit in SRC_SICR register set to 0, to reset cpu in case of FOSC < 40MHz
OSC_BYPASS fuse blown to 1, which should disable external oscillator during boot and so if restart is caused by CMU_OLR, we can wait in u-boot for external clock recovery
The problem is that module always goes to Serial Download Mode after power up if OSC_BYPASS fuse is blown to 1.
We have modified u-boot so it configures external clocks properly and it works if loaded using serial downloader. Unfortunately, doesn’t work when u-boot should be loaded from NAND (after power up).
Could you provide the software version of your module? Which carrier board are you using?
we are trying to configure our module in way that it can survive temporary external clock (crystal) malfunction.
What is your application? Why do you need this functionality?
The problem is that module always goes to Serial Download Mode after power up if OSC_BYPASS fuse is blown to 1.
We have modified u-boot so it configures external clocks properly and it works if loaded using serial downloader. Unfortunately, doesn’t work when u-boot should be loaded from NAND (after power up).
Could you provide the software version of your module? Which carrier board are you using?
We are using U-Boot 2016.11. We are using our custom carrier board, but we discovered the same behavior with Iris Carrier Board.
What is your application? Why do you need this functionality?
We need to certificate our device according to EN 50131-1/EN50131-3. One of its requirement is recovering from fault condition, e.g. from temporary clock signal failure.
Could you provide an error log?
AFAIK, there is no error log at all. The device after power up goes directly to serial download mode (and responds to 0x23454523 pattern). It looks like u-boot doesn’t start at all - we are sure about this (no output on console, we are controlling LED on our carrier board in early stage of u-boot and it doesn’t blink. LED works on board without OSC_BYPASS fuse blown).
I’d like to underline, that everything works fine if OSC_BYPASS fuse is not blown.
We don’t have any experience blowing this special OSC_BYPASS fuse as we never did this.
** The only fusing tested by Toradex is the official Fusing. Any changes to this Fusing are the Responsibility of the customer and lead to loss of warranty. **
Being that said, the only thing I found is that maybe your need to enable the FIRC. Further you should ask this question in the NXP Community.
