Create data logging subsystem

Create a subsystem which can log data to both SD cards simultaeneously (Teensy SD card and SPI SD card) as well as any other storage devices (flash chips etc)

This is quite challenging, as the Teensy SDIO doesn't have much documentation, and the SdFat documentation is hard to understand.

The difficulty here is that we need to keep two files "open" on two different SD cards.

Some pointers to get started:

SD library source code for Teensy - contains how SdFat is used in the background to provide the familiar SD.h Arduino API
Example of using two SD cards with SdFat

The data logging format doesn't matter at the moment. All we need to be able to do is write bytes to the SD cards, and we can figure out the rest a bit later. To begin with it will likely be CSV strings, but don't worry about this detail for now.

The data logging subsystem will subscribe directly to the data sources (ie Sensor_ADXL375) so no need to worry about how it gets the data for time being. Just demonstrate logging of bytes to both cards each loop, and try to benchmark their performance (relative to what we saw before by just using SD library with Teensy SDIO)

@robosam2003 I would appreciate you looking at this since you used SdFat on Daedalus and have a bit more experience with the library.

TeamSunride / MRAS

Create data logging subsystem #25