I have experience with Kinetis and SPI, but this is my first time bringing up an SD card interface. Starting with a TWR-K20D72M tower board, I have wired a microSD card (proto board from MicroElectronika) to SPI0 through the TWRPI connector J8.
The init sequence is well known, and I'm 95% sure the signals are getting to the card, but the MISO line seems to not be driven properly by the card. It's just some sort of reflection. A couple of scope shots of CMD0 are attached. The clock speed is ~ 180 KHz.
I've seen a couple old postings of this issue in other forums, but no solution. Anybody seen this before, and know what it means? Any advice appreciated!