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:
*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:
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ANNEX INFO
We have replicated the boot_mode control circuit of the EVK (Image1) for our circuit (Image2).
*Notes:
Image 1: BOOT MODE Circuit on Evaluation Kit
Image 2: Our BOOT MODE Circuit
Hi @benjamincanton,
Please try changing the R72 from 10k to 1k and see if that helps.
Also, please let me know the power-on sequence, it would be better if you could share the schematic with us.
Thanks & Regards,
Dhruvit Vasavada
A solution was found to the problem above as follows:
- When devices are first received they are in SD/MMC Manufacture Mode by default. In this mode boot pins cannot be controlled externally.
- In order to control the pins externally, according to the diagram in page 1520 of the i.MX 7ULP Reference Manual (Doc number IMX7ULPRMB2, Rev. 0, 09/2020) two things need to happen
With the above settings the system boots from fuses and setting BOOT_MODE==1 (externally, through GPIO) forces Serial Download Mode (SDM), enabling software update externally in hardware with the circuit you had listed above.