Fast SDCard existence detect

[KanyeKanye]

If there is no SD Card in the slot, sdmmc_card_init returns (with 0x107) after about 29ms for SDMMC Mode and 21ms for SPI Mode.
It's way too long. How to detect SD card existence faster?

[mikemoy]

don't know why 21ms needs to be faster. A human cannot even react to 21ms.
But anyway, you can read or set up a IRQ to check the SDCard switch on the socket.

[KanyeKanye]

I have no more pins for CD pin. I store data in the loop and 28ms is much too long for waiting. I believe there is some way (sanding some CMDx command) that would answer immediately on every card.