I have an FPGA (Lattice ICE40UP5K) at hand and need to do some SD card I/O with it. There are tutorials about interfacing with an SD card with an FPGA, but they typically concern with the case where the card is connected directly to FPGA via some soldering work. However, I want to use an SD card adapter (like this one) for more flexibility, and I'm not sure if these tutorials apply to my use case.
In particular, I wonder what do the adapters do besides exposing the pads of SD cards to jumpers? I have tried hunting for the specification for them, but despite their ubiquitousness, I cannot find any spec for these little adapters :(
Here is a photo of my adapter. From the silk print I can tell they probably speak SPI, but can I just treat the adapted SD card like an SPI flash, without worrying about all the nasty details of the SD card specification? While I have learned that SD cards typically support the so-called SPI mode, the linked article also suggested that "The SPI mode is often used in microcontroller systems. With an FPGA, we might be better served with the SD modes". Which mode should I use with an adapter, then?
For your information, the smaller chip labeled
U1 has silk print
LVC125A WA15508 TXD19 05D
the larger chip labeled
U (which looks like an analog IC judging from its huge pins) has silk print
AMS1117 3.3 XJS68