In our design based on SABRE SDP, we try to implement 3 configurations for boot selection:
- eMMC via USDHC3
- external SD/MMC card via USDHC1
- SPI NOR flash via ECSPI1
Out of 32 EIM signals related with boot configuration, we are using only 2 in our design, specifically EIM_EB2 (E22) as SPI1_CS0 and EIM_EB3 (F23) as UART1_RI_B.
I already removed the series bus isolation resistors (4.7k) because they are not connected to anywhere, except for those two above. I have 2 questions to make sure what I did is correct:
I checked the reference manual for the related signals for boot selections. When I guarantee that the boot-up process will occur either from USDHC1, USDHC3 or ECSPI1;
1) Do I have to connect other unrelated boot signals to ground via 10k resistors? Or can I connect them directly to ground?
2) Since EIM_EB2 and EIM_EB3 are irrelevant for the mentioned boot selections, do I need any isolation or pull-down for them? (since I'm using them as low active signals, it would not be correct to pull them down)
Thanks in advance.