Only 11 years late to the game… with ESPs now ubiquitous (at 3.3V, so no level shifter needed), I ended up using SPI mode to get the raw image of an otherwise unaccessible SD card (and evtl ...

There are three SPI hosts on the ESP32 chip used here, 1 through 3. SPI1_HOST is used and it may be possible to get this working. The default application has SPI2_HOST and SPI3_HOST used for the ...