To ensure a successful boot from a carrier board SD card, we recommend reducing the SOM 5V to carrier board other powers (including SD circuit) delay time from 50ms to 25ms in custom carrier board.
Technical Justification
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POR Timing: The Zynq UltraScale+ MPSoC requires approximately 27ms to 30ms to exit the Power-On-Reset (POR) state and initiate the first boot commands.
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Back-drive Protection: During this reset interval, back drive from carrier board to any of the MPSoC IO pins are not allowed.
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Boot Media Synchronization: We had implemented some extra delay of 20ms delay for safer delay margin and provided in our user manual by considering eMMC as boot device (as eMMC is the default boot device). However, when booting from SD card, the above mentioned extra delay is not required.
For further inquiries, please get in touch with mktg@iwave-global.com
Please find the detailed G35D product information in the below link,