After much experimentation, I discovered that the extra ~30 seconds of BIOS power-on self test (POST) only occurred when an “SD Expansion Card” was plugged in to Slot 6 (the “forward-most” slot on the right-hand side, as per “Expansion Card Slot functionality on Framework Laptop 16 (AMD Ryzen™ AI 300 Series)”).
The issue occurs whether or not an SD card is inserted into the SD Expansion Card.
When the SD Expansion Card is plugged into any other slot, there is no extra boot delay. In fact, I performed 36 boot tests, with each of my six expansion cards plugged in to each of the six slots, one at a time, and the only test resulting in the delay was when the SD Expansion Card was in Slot 6.
(To be perfectly clear on which slot is affected, on my FW 16 mainboard, the reference designator is “JUSBC3”.)
I offered to be a “test bed” for a debug BIOS, to help figure out why the extra delay was happening. Instead, the FW support folks had me replace my original mainboard, then they had me replace the SD Expansion Card, and neither replacement resolved the delay issue. (The support folks were friendly and helpful throughout.)
After those replacements, they had their engineering team try to reproduce the issue, and they were unsuccessful. I asked for confirmation that their engineering teaming had tested with the “JUSBC3” slot and not some other “slot 6”, to make sure we were testing the same slot, but so far I’ve had no reply (12 days now).
To be fair, there is an easy workaround: Don’t put the SD Expansion Card in Slot 6. But, something odd is happening in POST when that card is in slot 6 on my FW16, and I’d like to know what that is, in case that issue could affect other mainboard operations.
(If the FW16 BIOS was open-sourced for anyone to compile, I’d put in my own debug code to figure out what was going on.)