Hello.
We have detected an erratic behaviour on our boot when we try to boot on SDM. Our design is based on iMX7ULP.
On our device we do not have a robust SDM boot when we apply Boot_MODE[1:0] = 01:
- On PTB4 (BOOT_MODE[0]) we have measured 1,27V when we apply 1V8 before R72.
- On PTB5 (BOOT_MODE[1]) we have 0V (Pull-down R74).
*Note: This are the same voltages that we have measured on EVK when SW1 is on position BOOT_MODE[1:0] = 01; on the EVK the SDM boot is robust.
On our device we have some PCBs that are not booting on SDM even with BOOT_MODE[1:0]=01 while others are properly booting on SDM. Even some PCBs are sometimes booting on SDM and sometimes not booting on SDM when BOOT_MODE[1:0] = 01. We have test it on several devices with not a clear conclusion.
When we fix BOOT_MODE[1:0]=01 and the PCB is not booting on SDM, the device seems to state on an Infinite Loop; as soon as we change to BOOT_MODE[1:0]=00 the system of the A7 boots.
Questions:
- Do you have any tips to understand where the problem may come from?
- Is there some knowed Errata or issue with the BOOT_MODES that we should consider to obtain the reason of a not robust SDM boot from BOOT_MODE[1:0] pins?
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ANNEX INFO
We have replicated the boot_mode control circuit of the EVK (Image1) for our circuit (Image2).
*Notes:
- R75 and R78 are not solded.
- Before R72 we apply 1V8 when we want to boot on SDM (BOOT_MODE[1:0]=01)
Image 1: BOOT MODE Circuit on Evaluation Kit
Image 2: Our BOOT MODE Circuit
