De-initialize/Reset SD Card to save power

[savejeff]

Found a solution. could this be tags as a feature request ?

Hi,

I'm working with an ESP32 based board that has already an inbuild SD Card Slot.
Looking into sleep current I noticed that the SD Card takes more power after sd.end than before sd.begin.

If I completely remove the sd card code but have the SD Card plugged in I get ~1mA (might be lower, limited by decimal points of measurement)
when I init the sd card and de-init it again, i get around 13-20 mA.
here is the interesting thing: in deep sleep, when i take out the sd card and put it in again it goes down to ~1mA.

Thus I conclude the sd card is after sd.end still held in some initialized state.
Is there a way besides cutting the power to the sd card with a transistor (which is not possible as the board is a given) to reset/de-init the sd card.

I read another thread from earlier that just stopping communicating with the sd would put it into a sleep state, I'm not seeing this. I tried putting all sd spi spins in input/input_pullup/input_pulldown and it didn't really help

[savejeff]

I Found a nice solution here:

https://forum.arduino.cc/t/resolved-how-can-i-reboot-an-sd-card/349700

sending 0xFF over SPI often enough will cause the SD Card to reset and send 0xFF back.
It can be used to reset a card that is stuck or not responding after a crash but also to "unmount" the sd card.

this simple code

pinMode(PIN_SPI_CS_SD, OUTPUT);
digitalWrite(PIN_SPI_CS_SD, LOW);

for(int i = 0; i < 10; i++)
{
  byte v = SPI.transfer(0xFF);
  if(v == 0xFF)
	  break;
}

digitalWrite(PIN_SPI_CS_SD, HIGH);

reduces the power consumption to sub 1mA after sd.end.

Would it be possible to add this to the sd.end code or add a sd.reset() function to also use it to reset a sd card if sd.begin fails?

[greiman]

Some cards remain active after chips select is high until they see a few clocks.

Try sending a 0XFF byte something like this with SD chip select high.

SPI.begin();
SPI.beginTransaction(SPISettings(400000, MSBFIRST, SPI_MODE0));
SPI.transfer(0XFF);
SPI.endTransaction();
SPI.end();

I will experiment with the sd.end() call to see if adding a transfer of an extra byte improves sleep.

You can't really put a card back in the initial power on state. You can only reinitialize a card. For example once a card is in SPI mode you must cycle power to use 4-bit SDIO mode.

[savejeff]

looks like i was a minutes faster with the solution.

Would look to have a sd.reset function added.

Might be helpful for some people when they have a system crash.

i can test this with a couple of sd cards. i have around 7 different types of sd cards here