NRF52832 (Nordic Thingy52 ) SD CARD problem

Also, using D11 for CS is a bit scary, because that's shared with the button on the Thingy?

Yes it is. I just unsoldered the button to avoid conflicts.

are you sure you haven't just wired it to the wrong pin on the SD card?

I am. In addition, I tried to remove the SD card just to be 100% sure there isn't any electrical conflict.

driving the SPI directly from prompt (ThingySpi.write(0xAA)) gives the exact waveform on the MOSI pin. Calling E.connectSDCard(ThingySpi, CS), E.unmountSD();, fs.appendFile(File,data) or even E.openFile(File) has no action on MOSI pin.

MOSI=D4;//P0.04
MISO=D3;//P0.03
SCK=D2;//P0.02
CS=D11;//P0.11

var ThingySpi = new SPI();
var csvLogFile="logFile.csv";

function Init()
{
  // Wire up up MOSI, MISO, SCK and CS pins (along with 3.3v and GND)
  ThingySpi.setup({mosi:MOSI, miso:MISO, sck:SCK});
  
  E.connectSDCard(ThingySpi, CS);
}


function csvLogSD(s)
{
  try{
    if(fs.appendFile(csvLogFile,s)==true)
      console.log("log saved");
  }catch(err){
    console.log("error writing to SD.. trying unmount+remount");
    E.unmountSD();
    E.connectSDCard(ThingySpi, CS);
  }
}