Hi,
I am trying to write data received via serial to a micro SD card. I am using an Arduino Portenta and breakout board with a built in SD slot. I have tried using the built in SD.h library but I can't figure out which pin to initiate to access the card. A lot of code I have looked at uses pin 10 but this isn't working for me. Does anybody know what pin I should be using?
I then started using the SDMMCBlockDevice.h and FATFileSystem.h libraries which works, this is where I found the code:
https://github.com/arduino/ArduinoCore-mbed/blob/main/libraries/Portenta_SDCARD/src/SDMMCBlockDevice.h
However, I believe the write speed associated with these libraries is very slow as I can only get it working at around 10-15 Hz. I need to be reading serial data at 100Hz and then writing it to the SD.
Not really sure what else I can do to increase the speed! 
Any help would be very much appreciated 
