You’re right. I thought I had erased eMMC, but it appears not. Thanks.
I’m now not able to get the board into MASKROM mode. The TST approach from the wiki doesn’t work. On the serial console, I see that it causes the “boot times” counter to reset to zero, but otherwise keeps loping.
I also tried the MRegister mode, but it’s not clear from the wiki what the “two pads of the M register” are. I see a single test-point labeled M, which based on the VIM3 schematics (I hope they are the same as VIM3L for this part) looks like TP7, connected to GND. Based on that, I connect R84 to TP7 and this seems to disable the eMMC.
However, this does not seem to enable USB boot for the MASKROM as expected. Rather, it continues to keep booting from the eMMC, but fails to load FIPs from eMMC.
Looking at the initial string
SM1:BL:511f6b:81ca2f;FEAT:A0F83180:20282000;POC:D;RCY:0;USB:0;EMMC:0;READ:0;0.0;CHK:0; it seems like the MASKROM is not detecting a USB connection (even though USB-C is conntected to host PC)